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Re: delamination dateline

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  • pennine56
    Hi Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have
    Message 1 of 23 , Jun 1, 2010
      Hi

      Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.

      From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.

      The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.

      regards
      David
    • mervhob
      Hi David, This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of
      Message 2 of 23 , Jun 1, 2010
        Hi David,

        This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.

        1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
        The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
        If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.

        2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
        It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.

        Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
        My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.

        Cheers,

        Merv

        --- In Microscope@yahoogroups.com, "pennine56" <pennine56@...> wrote:
        >
        > Hi
        >
        > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
        >
        > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
        >
        > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
        >
        > regards
        > David
        >
      • rhamvossen
        Hi Merv, Thanks for sharing a wealth of knowledge. I wonder if it would be possible for you to post some pictures of how your delaminated objectives look
        Message 3 of 23 , Jun 1, 2010
          Hi Merv,

          Thanks for sharing a wealth of knowledge. I wonder if it would be possible for you to post some pictures of how your delaminated objectives look through e.g. a phase telescope. I've seen delamination in Zeiss KPL and CPL eyepieces but so far not in Zeiss objectives. Maybe I haven't detected it yet...........I assume that delamination has many different faces. Would be good to see some images of "early", "middle" and "late" stages in the delamination process.

          Rolf

          --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@...> wrote:
          >
          >
          >
          >
          >
          >
          > Hi David,
          >
          > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
          >
          > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
          > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
          > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
          >
          > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
          > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
          >
          > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
          > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
          >
          > Cheers,
          >
          > Merv
          >
          > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
          > >
          > > Hi
          > >
          > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
          > >
          > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
          > >
          > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
          > >
          > > regards
          > > David
          > >
          >
        • pennine56
          ... Hello Merv Many thanks for your valuable insight. Yes, the chunky eyepiece doublet may have been a potential victim of its own weight. As remarked a few
          Message 4 of 23 , Jun 1, 2010
            --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@...> wrote:
            >
            >
            >
            >
            >
            >
            > Hi David,
            >
            > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
            >
            > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
            > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
            > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
            >
            > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
            > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
            >
            > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
            > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
            >
            > Cheers,
            >
            > Merv
            Hello Merv

            Many thanks for your valuable insight. Yes, the chunky eyepiece doublet may have been a potential victim of its own weight. As remarked a few years back in the forum, I stumbled on a fix for the delamination of this doublet, a days soak in acetone with a trace of immersion oil.

            No trace at all visually of the delamination remained after drying.

            Before (shown on a light panel)
            http://www.microscopy-uk.org.uk/mag/imgmar07/dwDSC_1370.jpg

            After
            http://www.microscopy-uk.org.uk/mag/imgmar07/dwDSC00619.jpg

            The same delamination pattern has just reappeared after three years so done a resoak.

            I think the solvent was driving oil into doublet the without separating elements and slowly dried out, so have sealed the edges of doublet with nail varnish the second time.

            with regards
            David
          • pennine56
            ... Hi Rolf The three delaminated optical planes in a 1970s Zeiss 40/1.0 planapo are photographed with a Betrand lens in the article below in case of interest.
            Message 5 of 23 , Jun 1, 2010
              --- In Microscope@yahoogroups.com, "rhamvossen" <r.vossen@...> wrote:
              >
              > Hi Merv,
              >
              > Thanks for sharing a wealth of knowledge. I wonder if it would be possible for you to post some pictures of how your delaminated objectives look through e.g. a phase telescope. I've seen delamination in Zeiss KPL and CPL eyepieces but so far not in Zeiss objectives. Maybe I haven't detected it yet...........I assume that delamination has many different faces. Would be good to see some images of "early", "middle" and "late" stages in the delamination process.
              >
              > Rolf
              Hi Rolf

              The three delaminated optical planes in a 1970s Zeiss 40/1.0 planapo are photographed with a Betrand lens in the article below in case of interest.

              http://www.microscopy-uk.org.uk/mag/artaug06/dw-delam.html

              The objective's performance is compared with a mint example of the same design.

              with regards
              David
            • mervhob
              Hi Rolf, I will see what I can do, one thing I have noticed is that delamination pictures do seem to depend on the age of the objective. The older objectives
              Message 6 of 23 , Jun 1, 2010
                Hi Rolf,

                I will see what I can do, one thing I have noticed is that delamination pictures do seem to depend on the age of the objective. The older objectives seem to show what used to be termed as 'balsam flowers' which do indeed look like flower petals, and seem to indicate a more percusive, localised failure. The newer objectives are similar to the ones shown in the link Dave provided to the Dave Walker article. The failures Dave Walker shows are similar to those I have on other Zeiss objectives. As Don suggested, the modern cements may be much less prone to this type of failure - I have a Spencer x90 NA 1.4 APO oil immersion which has slowly deteriorated over the last 15 years, which is very sad as its previous performance in terms of resolution and contrast could only be classed as fantastic. One day I might pluck up the courage to try and re-cement the back triplet using modern UV curing polymers - it would certainly be worth it!


                Best regards,

                Merv

                --- In Microscope@yahoogroups.com, "rhamvossen" <r.vossen@...> wrote:
                >
                > Hi Merv,
                >
                > Thanks for sharing a wealth of knowledge. I wonder if it would be possible for you to post some pictures of how your delaminated objectives look through e.g. a phase telescope. I've seen delamination in Zeiss KPL and CPL eyepieces but so far not in Zeiss objectives. Maybe I haven't detected it yet...........I assume that delamination has many different faces. Would be good to see some images of "early", "middle" and "late" stages in the delamination process.
                >
                > Rolf
                >
                > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@> wrote:
                > >
                > >
                > >
                > >
                > >
                > >
                > > Hi David,
                > >
                > > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
                > >
                > > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
                > > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
                > > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
                > >
                > > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
                > > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
                > >
                > > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
                > > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
                > >
                > > Cheers,
                > >
                > > Merv
                > >
                > > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
                > > >
                > > > Hi
                > > >
                > > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
                > > >
                > > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
                > > >
                > > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
                > > >
                > > > regards
                > > > David
                > > >
                > >
                >
              • rhamvossen
                Hi David, Thanks for the link. It appears to me that the effect of delamination is most visible in histological slides. The 25x planachro clearly performs
                Message 7 of 23 , Jun 2, 2010
                  Hi David,

                  Thanks for the link. It appears to me that the effect of delamination is most visible in histological slides. The 25x planachro clearly performs better than the delaminated planapo on the histological slides while the image with the apo is better on the diatom.

                  Rolf


                  > Hi Rolf
                  >
                  > The three delaminated optical planes in a 1970s Zeiss 40/1.0 planapo are photographed with a Betrand lens in the article below in case of interest.
                  >
                  > http://www.microscopy-uk.org.uk/mag/artaug06/dw-delam.html
                  >
                  > The objective's performance is compared with a mint example of the same design.
                  >
                  > with regards
                  > David
                  >
                • mecium.para
                  Now I have IR phobia... does anybody know if the filtration on an Ortho-Illuminator is adequate, or if I need to add something?
                  Message 8 of 23 , Jun 2, 2010
                    Now I have IR phobia... does anybody know if the
                    filtration on an Ortho-Illuminator is adequate, or
                    if I need to add something?

                    --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@...> wrote:
                    >
                    >
                    >
                    >
                    >
                    >
                    > Hi David,
                    >
                    > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
                    >
                    > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
                    > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
                    > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
                    >
                    > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
                    > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
                    >
                    > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
                    > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
                    >
                    > Cheers,
                    >
                    > Merv
                    >
                    > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
                    > >
                    > > Hi
                    > >
                    > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
                    > >
                    > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
                    > >
                    > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
                    > >
                    > > regards
                    > > David
                    > >
                    >
                  • rene
                    ... Yes, a LED. :-) Seriously, if a camera doesn t go berserk, you re probably ok. A typical IR filter has a bit of a greenish tint, in my illuminator
                    Message 9 of 23 , Jun 3, 2010
                      > Now I have IR phobia... does anybody know if the
                      > filtration on an Ortho-Illuminator is adequate, or
                      > if I need to add something?

                      Yes, a LED. :-)

                      Seriously, if a camera doesn't go berserk, you're probably ok. A typical IR filter has a bit of a greenish tint, in my illuminator (diavert) it might be included in the diffusing filter. The daylight (blue) filters take away most of it in any case. If not sure, take an IR filter from an old slide projector.

                      Rene






                      >
                      > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@> wrote:
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > > Hi David,
                      > >
                      > > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
                      > >
                      > > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
                      > > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
                      > > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
                      > >
                      > > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
                      > > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
                      > >
                      > > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
                      > > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
                      > >
                      > > Cheers,
                      > >
                      > > Merv
                      > >
                      > > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
                      > > >
                      > > > Hi
                      > > >
                      > > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
                      > > >
                      > > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
                      > > >
                      > > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
                      > > >
                      > > > regards
                      > > > David
                      > > >
                      > >
                      >
                    • rhamvossen
                      I just wonder how much IR radiation you really receive from a microsope. You must have a very strong illumininator then. IR radiation is nothing else than
                      Message 10 of 23 , Jun 3, 2010
                        I just wonder how much IR radiation you really receive from a microsope. You must have a very strong illumininator then. IR radiation is nothing else than heat, so while looking into a camping fire you will receive much more IR than from a microscope as you often feel the heat in your eyes. And what about those hot sunny days in which you really feel the heat?

                        Rolf

                        --- In Microscope@yahoogroups.com, "mecium.para" <mecium.para@...> wrote:
                        >
                        > Now I have IR phobia... does anybody know if the
                        > filtration on an Ortho-Illuminator is adequate, or
                        > if I need to add something?
                        >
                        > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@> wrote:
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > > Hi David,
                        > >
                        > > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
                        > >
                        > > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
                        > > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
                        > > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
                        > >
                        > > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
                        > > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
                        > >
                        > > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
                        > > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
                        > >
                        > > Cheers,
                        > >
                        > > Merv
                        > >
                        > > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
                        > > >
                        > > > Hi
                        > > >
                        > > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
                        > > >
                        > > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
                        > > >
                        > > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
                        > > >
                        > > > regards
                        > > > David
                        > > >
                        > >
                        >
                      • mervhob
                        Hi Rolf and other IR worriers, The peak of output from a tungsten halogen lamp is in the near IR, peaking at circa 1 micron wavelength. The heat radiation from
                        Message 11 of 23 , Jun 3, 2010
                          Hi Rolf and other IR worriers,

                          The peak of output from a tungsten halogen lamp is in the near IR, peaking at circa 1 micron wavelength. The heat radiation from your camp fire peaks up between 10 - 15 microns wavelength and this will not pass through crown glass, which shuts off above 4 microns wavelength. Conventional window glass, which has a greenish tint due to iron doping, is very effective at stopping long and medium wave IR, but is completely transparent to the near IR. If we compare the output from a 60W TH lamp at 1 micron and 550 nm, the near IR output is 3.3 times the radiance at yellow-green, and the integrated difference over their respective bandwidths is even greater. Less than 20% of a tungsten-halogen lamps output is in the visible; a 60W lamp radiates 48W in the near and far IR!
                          As Rene points out, the IR filters from old slide projectors are a good source of protection - these are mostly 2" or 50mm square. These cut off most of the near IR which would otherwise fry your 35mm slides with a 300W tungsten projector bulb! And if the colour rendition of your CCD or CMOS camera goes barmy, it is very likely to be excessive near IR radiation - the filters on most cameras are not designed to deal with the condensed near IR radiation of a 100W TH lamp.

                          The tungsten incandescent lamp is a very inefficient (but convenient) lighting source. As Edison boasted in the 1880s, 'He would generate electricity so cheaply that only the rich would use candles!'
                          Now we have excited phosphor LED lamps, all these worries will soon be a thing of the past, but in the case of precious and well loved objectives, it pays to be careful!

                          Cheers,

                          Merv

                          --- In Microscope@yahoogroups.com, "rhamvossen" <r.vossen@...> wrote:
                          >
                          > I just wonder how much IR radiation you really receive from a microsope. You must have a very strong illumininator then. IR radiation is nothing else than heat, so while looking into a camping fire you will receive much more IR than from a microscope as you often feel the heat in your eyes. And what about those hot sunny days in which you really feel the heat?
                          >
                          > Rolf
                          >
                          > --- In Microscope@yahoogroups.com, "mecium.para" <mecium.para@> wrote:
                          > >
                          > > Now I have IR phobia... does anybody know if the
                          > > filtration on an Ortho-Illuminator is adequate, or
                          > > if I need to add something?
                          > >
                          > > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@> wrote:
                          > > >
                          > > >
                          > > >
                          > > >
                          > > >
                          > > >
                          > > > Hi David,
                          > > >
                          > > > This is one of those stories which will run and run! I will try and list the most likely causes, based on what I have observed over a large amount of material.
                          > > >
                          > > > 1) Thermal - in the case of objectives the most likely cause of failure, in particular now high powered filament lamps are so common. It is not completely clear whether this is differential expansion at the interface between different materials, or, heating at the interface itself. Our Victorian predecessors used paraffin (kerosene) lamps, often with a water cell. I have been experimenting with a paraffin lamp, and to my surprise, the heating in the lamp condenser is very small compared to that of a tungsten lamp. This observation is confirmed by statements from 19th century microscopists. Tungsten lamps produce far more energy in the near IR, in particular up to 4.6 microns wavelength, where most glasses become opaque. The thickness of a microscope slide will stop the long wave IR from the lamp dead, however the peak of energy from a tungsten lamp is circa 1 - 2 microns, not in the visible.
                          > > > The physics of what happens at the interface between cemented elements is quite complex, in particular where one of the materials is single crystal, and does not seem to have been investigated in recent history - though the photonics guys may be showing an interest!
                          > > > If conditions at the interface are such as to cause selective heating in the cement, this could readily increase the possibility of failure.
                          > > >
                          > > > 2) Physical - this may or may not be directly observable as damage to the elements or their mountings. The mystery of the Zeiss wide angle Kpl oculars is possibly explained by the fact that they are very heavy lumps of glass! Glass is a very stiff elastic material with a high propagation velocity for sound. As every glass cutter knows, a slight scratch on the surface, followed by a sharp tap from the cutter handle leads to two beautifully cleanly severed pieces of glass (or not.....)
                          > > > It is the very high acoustic energy, and its concentration at the scratch which does the business. An acoustic bulk wave travelling in glass - or a single crystal material - can have a very long decay time - the material has a very high Q or 'Quality factor'. The wave will be reflected at the interfaces, and the structure will tend to resonate leading to a standing wave. We used to make acoustic delay lines for moving target indicator(MTI) radar using quartz or glass, based on this very useful property. You may drop or knock over your eyepieces or objectives several times without any effect, but eventually..... If I have some single crystal material or glass chucked up on the lathe using cement, a sharp tap will cause it to fall off, even though the lapping and grinding operations have failed to do so. The energy concentration at the interface has to pass through a threshold for the crack to propagate - as predicted by Griffith's crack propagation theory.
                          > > >
                          > > > Exactly why Zeiss seem to be so prone to failure is not completely explained - Out of some 12 prewar Zeiss APOs and Fluorites, only one is good, and with post war metallurgical objectives, the statistic is worse, and this may be evidence in favour of the heating theory. My LOMO APOs from the 60s through to the 90s show no signs of failure - but I always use them with adequate IR filtering.
                          > > > My opinion, based on a drawer full of dead objectives, is that all these objecives using mixed materials are birds of passage - enjoy them while you may. But you can prolong their useful existance by suitable precautions.
                          > > >
                          > > > Cheers,
                          > > >
                          > > > Merv
                          > > >
                          > > > --- In Microscope@yahoogroups.com, "pennine56" <pennine56@> wrote:
                          > > > >
                          > > > > Hi
                          > > > >
                          > > > > Interesting thread. From my 70s Zeiss scope experiences (Standards, Photomic III) the problem seems quite wide for their optical systems of this era. I have a badly delaminated doublet in the Zeiss Kpl 10x W eyepiece, a large element with gentle curves, also have seen splitting doublets on the intermediate heads for Standards.
                          > > > >
                          > > > > From the objectives I've had, the delaminations spreads across most of the range, I've had badly delaminated examples of 70s achros, planachros and planapos.
                          > > > >
                          > > > > The cooking with the large lamps as has been raised seems one likely factor but don't understand why large elements in eyepieces would do so.
                          > > > >
                          > > > > regards
                          > > > > David
                          > > > >
                          > > >
                          > >
                          >
                        • pennine56
                          ... Hi Rolf Failing an ex slide projector filter as suggested, the Schott KG range is a typical heat absorbing filter. In UK the 25mm circles are much cheaper
                          Message 12 of 23 , Jun 3, 2010
                            --- In Microscope@yahoogroups.com, "rhamvossen" <r.vossen@...> wrote:
                            >
                            > I just wonder how much IR radiation you really receive from a microsope. You must have a very strong illumininator then. IR radiation is nothing else than heat, so while looking into a camping fire you will receive much more IR than from a microscope as you often feel the heat in your eyes. And what about those hot sunny days in which you really feel the heat?
                            >
                            > Rolf
                            >

                            Hi Rolf

                            Failing an ex slide projector filter as suggested, the Schott KG range is a typical heat absorbing filter. In UK the 25mm circles are much cheaper than the larger squares. I bought a 3mm thick toughened glass KG1 25mm for <£10 from Knight Optical online shop.

                            It sits permanently in the deep filter tray on my Zeiss Photomicroscope III as not clear if there is one fitted and given the quirky Zeiss optics as run the 100W lamp at full intensity quite a lot.

                            regards
                            David
                          • William J Fassnacht
                            Hello, I have two Zeiss microsopes, circa late 1970 s, early 1980 s. I have asked the same questions. The following is an excerpt distilled from information
                            Message 13 of 23 , Jun 3, 2010
                              Hello,
                              I have two Zeiss microsopes, circa late 1970's, early 1980's. I have
                              asked the same questions.
                              The following is an excerpt distilled from information relayed to me
                              from a certified Zeiss technician and
                              a Zeiss designer from Germany.
                              "1. Unless the conditions that caused the delamination continued
                              into the optics present use the delamination normally does not get
                              progressively worse.
                              2. Leaving a high wattage Xenon, Mercury, etc. lamp on during working
                              hours even when the microscope is not being used produces enough heat to
                              "cook" the eyepiece, objective, or prism. Cooking causes delamination.
                              3. In the past Zeiss would use a number of "exotic" adhesives to cement
                              their eyepieces, objectives, and prisms to achieve the highest "optical"
                              qualities possible. The longevity of these "exotic" adhesives was not
                              very good.
                              4. The "exotic" adhesives, plus "cooking" by very hot lamps, and sudden
                              extreme temperature changes could cause delamination."

                              Depending on your specific microscope technique, i.e. Brightfield,
                              Darkfield, DIC, Pol, Phase, Oblique, etc. and illumination,
                              Incandescent, HBO, Xenon, Halogen, etc. Zeiss
                              offered two typs of thermal protective filters. Heat absorption filter
                              KG 1 and Heat reflection filter (Calflex).

                              Bill
                            • too_many_tools
                              So in time all DIC scopes will have delamination problems? TMT
                              Message 14 of 23 , Jul 16, 2010
                                So in time all DIC scopes will have delamination problems?

                                TMT

                                --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@...> wrote:
                                >
                                >
                                >
                                >
                                >
                                >
                                > John,
                                >
                                > Wollaston prisms are made of single crystal quartz, which has slightly different coefficients of expansion, depending on the orientation to the optic axis. Also, Wollaston prisms are not normally cemented with balsam, as this would be a poor match to the refractive index of quartz and we do not want total reflection of one component at the interface as is the case with a Nicol. Traditionally, castor oil or glycerine was used. In some cases, a particular mixture may have been used, which may not have been long term stable. The crystallographic axis of each section on the Wollaston are crossed, and the prism angle set so as to provide equal deviation of the ordinary and extraordinary rays. In Nomarski's modification of the Wollaston the situation is complicated by the fact that one set of axis is tilted, so as to localise the fringes outside the prism, and this is the modification normally used on DIC microscopes. A further complication is that quartz is piezoelectric, and this may also have an influence over temperature. The fact is that if you heat a bar of single crystal quartz, because it is not isotropic it will not remain flat, and the degree of out of flatness will depend on the orientation of the axis with respect to the plane surface. Thus two surfaces cut with misaligned axis will have a tendancy to separate with time and temperature change. Glass is pretty isotropic being a supercooled liquid, but optical instruments built with single crystal materials, in particular those with cemented elements all tend to have long term problems.
                                >
                                > Cheers,
                                >
                                > Merv
                                >
                                > --- In Microscope@yahoogroups.com, "J. Forster" <jfor@> wrote:
                                > >
                                > > Hi,
                                > >
                                > > How does your theory explain the very common delamination of the Wolloston
                                > > prisms in the Zeiss INKO DIC objectives. The mating surfaces are flat.
                                > >
                                > > -John
                                > >
                                > > ===============
                                > >
                                > >
                                > >
                                > > >
                                > > > The problem with the Zeiss objectives I have examined is generally between
                                > > > fluorite/glass interfaces, in particular those in the back triplet. In the
                                > > > 1930s, Zeiss designers were prone to push the limits, using very deep
                                > > > curvatures in order to maximise their capability to provide correction
                                > > > with existing glasses. This merely exacerbated a problem that was bound to
                                > > > occur with the expansion mismatch between fluorite and glass, a problem
                                > > > made worse by the variability in samples of natural fluorite. I do not
                                > > > believe that there was significant difference in the type of balsam used,
                                > > > and I have a drawer full of delaminated APOs and Fluorite objectives -
                                > > > Zeiss, Leitz, Spencer, Beck, Swift, Vickers, CTS, Reichert etc. By far the
                                > > > most frequent culprit is Zeiss, with examples into the 1960s.
                                > > > In contrast I have Victorian objectives, standard achromats of all origins
                                > > > including Zeiss without a trace of delamination, except where physical
                                > > > damage has occurred. With modern glasses, requiring less extreme curvature
                                > > > to achieve correction of aberrations, the problem has diminished, but as
                                > > > Gordon has rightly pointed out it is dependent on the temperature extremes
                                > > > seen by objectives, and the number of times it is subjected to those
                                > > > extremes.
                                > > >
                                > > > Cheers,
                                > > >
                                > > > Merv
                                > >
                                >
                              • J. Forster
                                Castor Oil and Glycerin do not set up . Do you mean that they leak out of the interstice and leave an air bubble which APPEARS to be de-lamination? -John
                                Message 15 of 23 , Jul 17, 2010
                                  Castor Oil and Glycerin do not "set up". Do you mean that they leak out of
                                  the interstice and leave an air bubble which APPEARS to be de-lamination?

                                  -John

                                  ==============


                                  > So in time all DIC scopes will have delamination problems?
                                  >
                                  > TMT
                                  >
                                  > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@...> wrote:
                                  >>
                                  >>
                                  >>
                                  >>
                                  >>
                                  >>
                                  >> John,
                                  >>
                                  >> Wollaston prisms are made of single crystal quartz, which has slightly
                                  >> different coefficients of expansion, depending on the orientation to the
                                  >> optic axis. Also, Wollaston prisms are not normally cemented with
                                  >> balsam, as this would be a poor match to the refractive index of quartz
                                  >> and we do not want total reflection of one component at the interface as
                                  >> is the case with a Nicol. Traditionally, castor oil or glycerine was
                                  >> used. In some cases, a particular mixture may have been used, which may
                                  >> not have been long term stable. The crystallographic axis of each
                                  >> section on the Wollaston are crossed, and the prism angle set so as to
                                  >> provide equal deviation of the ordinary and extraordinary rays. In
                                  >> Nomarski's modification of the Wollaston the situation is complicated by
                                  >> the fact that one set of axis is tilted, so as to localise the fringes
                                  >> outside the prism, and this is the modification normally used on DIC
                                  >> microscopes. A further complication is that quartz is piezoelectric, and
                                  >> t!
                                  > his may also have an influence over temperature. The fact is that if you
                                  > heat a bar of single crystal quartz, because it is not isotropic it will
                                  > not remain flat, and the degree of out of flatness will depend on the
                                  > orientation of the axis with respect to the plane surface. Thus two
                                  > surfaces cut with misaligned axis will have a tendancy to separate with
                                  > time and temperature change. Glass is pretty isotropic being a
                                  > supercooled liquid, but optical instruments built with single crystal
                                  > materials, in particular those with cemented elements all tend to have
                                  > long term problems.
                                  >>
                                  >> Cheers,
                                  >>
                                  >> Merv
                                  >>
                                  >> --- In Microscope@yahoogroups.com, "J. Forster" <jfor@> wrote:
                                  >> >
                                  >> > Hi,
                                  >> >
                                  >> > How does your theory explain the very common delamination of the
                                  >> Wolloston
                                  >> > prisms in the Zeiss INKO DIC objectives. The mating surfaces are flat.
                                  >> >
                                  >> > -John
                                  >> >
                                  >> > ===============
                                  >> >
                                  >> >
                                  >> >
                                  >> > >
                                  >> > > The problem with the Zeiss objectives I have examined is generally
                                  >> between
                                  >> > > fluorite/glass interfaces, in particular those in the back triplet.
                                  >> In the
                                  >> > > 1930s, Zeiss designers were prone to push the limits, using very
                                  >> deep
                                  >> > > curvatures in order to maximise their capability to provide
                                  >> correction
                                  >> > > with existing glasses. This merely exacerbated a problem that was
                                  >> bound to
                                  >> > > occur with the expansion mismatch between fluorite and glass, a
                                  >> problem
                                  >> > > made worse by the variability in samples of natural fluorite. I do
                                  >> not
                                  >> > > believe that there was significant difference in the type of balsam
                                  >> used,
                                  >> > > and I have a drawer full of delaminated APOs and Fluorite objectives
                                  >> -
                                  >> > > Zeiss, Leitz, Spencer, Beck, Swift, Vickers, CTS, Reichert etc. By
                                  >> far the
                                  >> > > most frequent culprit is Zeiss, with examples into the 1960s.
                                  >> > > In contrast I have Victorian objectives, standard achromats of all
                                  >> origins
                                  >> > > including Zeiss without a trace of delamination, except where
                                  >> physical
                                  >> > > damage has occurred. With modern glasses, requiring less extreme
                                  >> curvature
                                  >> > > to achieve correction of aberrations, the problem has diminished,
                                  >> but as
                                  >> > > Gordon has rightly pointed out it is dependent on the temperature
                                  >> extremes
                                  >> > > seen by objectives, and the number of times it is subjected to those
                                  >> > > extremes.
                                  >> > >
                                  >> > > Cheers,
                                  >> > >
                                  >> > > Merv
                                  >> >
                                  >>
                                  >
                                  >
                                  >
                                  >
                                  > ------------------------------------
                                  >
                                  > Yahoo! Groups Links
                                  >
                                  >
                                  >
                                  >
                                • gc_couger
                                  TMT, It is not a forgone conclusion all DIC optics will fail. But they sure don t withstand abuse very well. Using fiber optic light source of less than 100
                                  Message 16 of 23 , Jul 17, 2010
                                    TMT,

                                    It is not a forgone conclusion all DIC optics will fail. But they sure don't withstand abuse very well. Using fiber optic light source of less than 100 watts and storing the microscope in the house where it stays between 0/50 C or 32/122 f with no changes more rapid than a person can stand should keep any optic that has no signs of delamination just fine.

                                    I keep the ones that have started to come apart stored in an insulated box so any changed in temperature happen more slowly.

                                    It is not just DIC optics but all older Zeiss glass that has a problem. Some say they were in love with an older cement that was prone to delaminated others say their lenses have more radical curvature. I expect there is some truth to them all.

                                    It is hard to measure and photograph but not hard to see that things look better under a Zeiss to many of us. It may be as an old auctioneer friend of mine used to say, "The more you pay the better you'll like it" but a lot of folks are willing to pay the price.

                                    Gordon

                                    --- In Microscope@yahoogroups.com, "too_many_tools" <too_many_tools@...> wrote:
                                    >
                                    > So in time all DIC scopes will have delamination problems?
                                    >
                                    > TMT
                                    >
                                    > --- In Microscope@yahoogroups.com, "mervhob" <merv.hobden@> wrote:
                                    > >
                                    > >
                                    > >
                                    > >
                                    > >
                                    > >
                                    > > John,
                                    > >
                                    > > Wollaston prisms are made of single crystal quartz, which has slightly different coefficients of expansion, depending on the orientation to the optic axis. Also, Wollaston prisms are not normally cemented with balsam, as this would be a poor match to the refractive index of quartz and we do not want total reflection of one component at the interface as is the case with a Nicol. Traditionally, castor oil or glycerine was used. In some cases, a particular mixture may have been used, which may not have been long term stable. The crystallographic axis of each section on the Wollaston are crossed, and the prism angle set so as to provide equal deviation of the ordinary and extraordinary rays. In Nomarski's modification of the Wollaston the situation is complicated by the fact that one set of axis is tilted, so as to localise the fringes outside the prism, and this is the modification normally used on DIC microscopes. A further complication is that quartz is piezoelectric, and this may also have an influence over temperature. The fact is that if you heat a bar of single crystal quartz, because it is not isotropic it will not remain flat, and the degree of out of flatness will depend on the orientation of the axis with respect to the plane surface. Thus two surfaces cut with misaligned axis will have a tendancy to separate with time and temperature change. Glass is pretty isotropic being a supercooled liquid, but optical instruments built with single crystal materials, in particular those with cemented elements all tend to have long term problems.
                                    > >
                                    > > Cheers,
                                    > >
                                    > > Merv
                                    > >
                                    > > --- In Microscope@yahoogroups.com, "J. Forster" <jfor@> wrote:
                                    > > >
                                    > > > Hi,
                                    > > >
                                    > > > How does your theory explain the very common delamination of the Wolloston
                                    > > > prisms in the Zeiss INKO DIC objectives. The mating surfaces are flat.
                                    > > >
                                    > > > -John
                                    > > >
                                    > > > ===============
                                    > > >
                                    > > >
                                    > > >
                                    > > > >
                                    > > > > The problem with the Zeiss objectives I have examined is generally between
                                    > > > > fluorite/glass interfaces, in particular those in the back triplet. In the
                                    > > > > 1930s, Zeiss designers were prone to push the limits, using very deep
                                    > > > > curvatures in order to maximise their capability to provide correction
                                    > > > > with existing glasses. This merely exacerbated a problem that was bound to
                                    > > > > occur with the expansion mismatch between fluorite and glass, a problem
                                    > > > > made worse by the variability in samples of natural fluorite. I do not
                                    > > > > believe that there was significant difference in the type of balsam used,
                                    > > > > and I have a drawer full of delaminated APOs and Fluorite objectives -
                                    > > > > Zeiss, Leitz, Spencer, Beck, Swift, Vickers, CTS, Reichert etc. By far the
                                    > > > > most frequent culprit is Zeiss, with examples into the 1960s.
                                    > > > > In contrast I have Victorian objectives, standard achromats of all origins
                                    > > > > including Zeiss without a trace of delamination, except where physical
                                    > > > > damage has occurred. With modern glasses, requiring less extreme curvature
                                    > > > > to achieve correction of aberrations, the problem has diminished, but as
                                    > > > > Gordon has rightly pointed out it is dependent on the temperature extremes
                                    > > > > seen by objectives, and the number of times it is subjected to those
                                    > > > > extremes.
                                    > > > >
                                    > > > > Cheers,
                                    > > > >
                                    > > > > Merv
                                    > > >
                                    > >
                                    >
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