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Re: [Microscope] Re: Leitz Wetzlar Wedge for Microscope

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  • Salvatore Previtera
    Hi Don, I like very much your approach. At my first experiences with polarized light, I was rather scared of the many precautions to be taken in using the
    Message 1 of 23 , Nov 1, 2005
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      Hi Don,
      I like very much your approach.
      At my first experiences with polarized light, I was rather scared of the
      many precautions to be taken in using the fully equipped Zeiss polarization
      scope with teodolitic stage available in the lab, and I decided to build a
      simple device, all in plexiglas, made only of a polarizer, a sample
      holder(with the possibility of 0-60° inclination apart from rotation), a
      slot for the auxiliary sheet (compensator, first order red, etc.) and an
      analyzer.
      With this device we learned very well to evaluate the tridimensional index
      surface of biaxially oriented plastic films, a not very immediate task ( a
      lot of trigonometric calculations and dummy results if the measurements were
      not precise).
      Later we applied what learned to the microscope observations.
      About the usage of mica, I also used it, but also with good result, simple
      sheets of packaging films, from cellophane to oriented polypropilene,
      stacking several sheets to add retardation.
      In addition, I think that you can make a good wedge by cutting a sheet of
      plexiglas (possibly trapezoidal) and stretch it at 100 degrees or somewhat
      higher temperature, and cooling it while stretched.
      The trapezoidal shape allows more stretching in the region of shorter width,
      and a gradual retardation (a wedge), can be observed along the sheet.
      Regards,
      Salvatore

      ----- Original Message -----
      From: "D. Halterman" <djhmis@...>
      To: <Microscope@yahoogroups.com>
      Sent: Tuesday, November 01, 2005 12:05 AM
      Subject: RE: [Microscope] Re: Leitz Wetzlar Wedge for Microscope


      >
      > It's a lot of reading, and I hope you don't think I
      > dumped a big homework assignment on you. However,
      > that is a great site with fun interactive tutorials,
      > and I thought it would be better in the long run for
      > you to really learn about PLM than have me cobble
      > together a condensed, and probably confusing,
      > illustration of what that plate does.
      >
      > Ian, if you retain an interest in polarization for
      > your own microscopy, don't worry about needing
      > expensive equipment at first. You can establish basic
      > polarization with two small pieces of polarizing
      > sheet, an optional 360 deg. round protractor for your
      > stage if you want to get fancy with extinction, and if
      > you have some patience you can make a "wedge" (a real
      > one) from sheets of mica, and in addition you can make
      > the "full wave" or "red" plate (as shown in that
      > auction) from sheet material as well. Many of the
      > materials you need are available from Edmund
      > Scientific and McCrone Microscopes and Accessories,
      > and they should both ship packets to England.
      >
      > If you are truly motivated, you can obtain a copy of
      > "The Petrographic Microscope: Evolution of a
      > Mineralogical Research Instrument" by Daniel E. Kile.
      > It has been praised as a classic in its field and a
      > must-read. (Disclosure: Dan is a friend, but he makes
      > no money from sales of this issue).
      >
      > http://www.modernmicroscopy.com/main.asp?article=35
      >
      > This is a vendor who sells copies of the issue
      > (Disclosure: I am a satisified, and somewhat broke,
      > customer of the Gemmary, but have no other
      > affiliation).
      >
      > http://www.gemmary.com/books/scibooks4.html
      >
      > As I say often these days: my time is limited, but I
      > will always try to answer questions by pointing you in
      > the right direction, or toward a useful website, and
      > in addition there are plenty of other people who will
      > help as well.
      >
      >
      > best,
      > Don
      >
      >
      > --- kenchy475 <kenchy475@...> wrote:
      >
      > > thanks Rene and Don
      > > i shall have a good read up on this now !
      > > regards
      > > Ian
      >
      >
      >
      > __________________________________
      > Yahoo! FareChase: Search multiple travel sites in one click.
      > http://farechase.yahoo.com
      >
      >
      >
      >
      > Yahoo! Groups Links
      >
      >
      >
      >
      >
      >
    • kenchy475
      wow Gordon that is a ton of info! thanks Ian
      Message 2 of 23 , Nov 1, 2005
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        wow Gordon that is a ton of info!
        thanks
        Ian
      • kenchy475
        this is becoming so interesting although i feel an information overload coming on! Ian ... From: Microscope@yahoogroups.com
        Message 3 of 23 , Nov 1, 2005
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          this is becoming so interesting although i feel an information overload
          coming on!
          Ian

          -----Original Message-----
          From: Microscope@yahoogroups.com [mailto:Microscope@yahoogroups.com]On
          Behalf Of Salvatore Previtera
          Sent: 01 November 2005 08:46
          To: Microscope@yahoogroups.com
          Subject: Re: [Microscope] Re: Leitz Wetzlar Wedge for Microscope


          Hi Don,
          I like very much your approach.
          At my first experiences with polarized light, I was rather scared of the
          many precautions to be taken in using the fully equipped Zeiss polarization
          scope with teodolitic stage available in the lab, and I decided to build a
          simple device, all in plexiglas, made only of a polarizer, a sample
          holder(with the possibility of 0-60° inclination apart from rotation), a
          slot for the auxiliary sheet (compensator, first order red, etc.) and an
          analyzer.
          With this device we learned very well to evaluate the tridimensional index
          surface of biaxially oriented plastic films, a not very immediate task ( a
          lot of trigonometric calculations and dummy results if the measurements were
          not precise).
          Later we applied what learned to the microscope observations.
          About the usage of mica, I also used it, but also with good result, simple
          sheets of packaging films, from cellophane to oriented polypropilene,
          stacking several sheets to add retardation.
          In addition, I think that you can make a good wedge by cutting a sheet of
          plexiglas (possibly trapezoidal) and stretch it at 100 degrees or somewhat
          higher temperature, and cooling it while stretched.
          The trapezoidal shape allows more stretching in the region of shorter width,
          and a gradual retardation (a wedge), can be observed along the sheet.
          Regards,
          Salvatore
        • Gordon Couger
          Dear Salvatore, It is amazing how much we learn from doing the experiment ourselves with devices we design and build ourselves. The time involved in design and
          Message 4 of 23 , Nov 1, 2005
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            Dear Salvatore,

            It is amazing how much we learn from doing the experiment ourselves with
            devices we design and build ourselves. The time involved in design and
            building really reinforces what we learn.

            So many treat a microscope a mysterious black box. When as you show in
            your work with polarized light the microscope is not needed or possibly in
            the way of understing what is going on.


            Gordon

            Salvatore Previtera wrote:
            > Hi Don,
            > I like very much your approach.
            > At my first experiences with polarized light, I was rather scared of the
            > many precautions to be taken in using the fully equipped Zeiss polarization
            > scope with teodolitic stage available in the lab, and I decided to build a
            > simple device, all in plexiglas, made only of a polarizer, a sample
            > holder(with the possibility of 0-60° inclination apart from rotation), a
            > slot for the auxiliary sheet (compensator, first order red, etc.) and an
            > analyzer.
            > With this device we learned very well to evaluate the tridimensional index
            > surface of biaxially oriented plastic films, a not very immediate task ( a
            > lot of trigonometric calculations and dummy results if the measurements were
            > not precise).
            > Later we applied what learned to the microscope observations.
            > About the usage of mica, I also used it, but also with good result, simple
            > sheets of packaging films, from cellophane to oriented polypropilene,
            > stacking several sheets to add retardation.
            > In addition, I think that you can make a good wedge by cutting a sheet of
            > plexiglas (possibly trapezoidal) and stretch it at 100 degrees or somewhat
            > higher temperature, and cooling it while stretched.
            > The trapezoidal shape allows more stretching in the region of shorter width,
            > and a gradual retardation (a wedge), can be observed along the sheet.
            > Regards,
            > Salvatore
            >
            > ----- Original Message -----
            > From: "D. Halterman" <djhmis@...>
            > To: <Microscope@yahoogroups.com>
            > Sent: Tuesday, November 01, 2005 12:05 AM
            > Subject: RE: [Microscope] Re: Leitz Wetzlar Wedge for Microscope
            >
            >
            >
            >>It's a lot of reading, and I hope you don't think I
            >>dumped a big homework assignment on you. However,
            >>that is a great site with fun interactive tutorials,
            >>and I thought it would be better in the long run for
            >>you to really learn about PLM than have me cobble
            >>together a condensed, and probably confusing,
            >>illustration of what that plate does.
            >>
            >>Ian, if you retain an interest in polarization for
            >>your own microscopy, don't worry about needing
            >>expensive equipment at first. You can establish basic
            >>polarization with two small pieces of polarizing
            >>sheet, an optional 360 deg. round protractor for your
            >>stage if you want to get fancy with extinction, and if
            >>you have some patience you can make a "wedge" (a real
            >>one) from sheets of mica, and in addition you can make
            >>the "full wave" or "red" plate (as shown in that
            >>auction) from sheet material as well. Many of the
            >>materials you need are available from Edmund
            >>Scientific and McCrone Microscopes and Accessories,
            >>and they should both ship packets to England.
            >>
            >>If you are truly motivated, you can obtain a copy of
            >>"The Petrographic Microscope: Evolution of a
            >>Mineralogical Research Instrument" by Daniel E. Kile.
            >>It has been praised as a classic in its field and a
            >>must-read. (Disclosure: Dan is a friend, but he makes
            >>no money from sales of this issue).
            >>
            >>http://www.modernmicroscopy.com/main.asp?article=35
            >>
            >>This is a vendor who sells copies of the issue
            >>(Disclosure: I am a satisified, and somewhat broke,
            >>customer of the Gemmary, but have no other
            >>affiliation).
            >>
            >>http://www.gemmary.com/books/scibooks4.html
            >>
            >>As I say often these days: my time is limited, but I
            >>will always try to answer questions by pointing you in
            >>the right direction, or toward a useful website, and
            >>in addition there are plenty of other people who will
            >>help as well.
            >>
            >>
            >>best,
            >>Don
            >>
            >>
            >>--- kenchy475 <kenchy475@...> wrote:
            >>
            >>
            >>>thanks Rene and Don
            >>>i shall have a good read up on this now !
            >>>regards
            >>>Ian
            >>
            >>
            >>
            >>__________________________________
            >>Yahoo! FareChase: Search multiple travel sites in one click.
            >>http://farechase.yahoo.com
            >>
            >>
            >>
            >>
            >>Yahoo! Groups Links
            >>
            >>
            >>
            >>
            >>
            >>
            >
            >
            >
            >
            >
            >
            > Yahoo! Groups Links
            >
            >
            >
            >
            >
            >
            >
          • Gordon Couger
            Ian, I stared collecting information like that for myself and that shows what being familur with a good Internet bibliography can do in a about 15 minutes time
            Message 5 of 23 , Nov 1, 2005
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              Ian,

              I stared collecting information like that for myself and that shows what
              being familur with a good Internet bibliography can do in a about 15
              minutes time and I file a copy for the next time.

              Gordon

              kenchy475 wrote:
              > wow Gordon that is a ton of info!
              > thanks
              > Ian
              >
              >
              >
              >
              >
              >
              >
              >
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
              >
              >
              >
            • David Littlewood
              In message , kenchy475 writes ... Ian, At the risk of overloading a few more of your
              Message 6 of 23 , Nov 1, 2005
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                In message <DJENLJHAKHOJPNAFDNOKCEOLDAAA.kenchy475@...>, kenchy475
                <kenchy475@...> writes
                >thanks for the info and links Don and thanks for the extra input David re
                >the Quekett - its all a bit clearer now and certainly the ebay item has now
                >sprung to life instead of being just a piece of flat metal with what
                >appeared to be a hole in it - i can relate it to my scopes now - dont know
                >if i'll get the time to make up anything at the mo but i will keep my eye
                >out for any bits that may come my way now that i know a bit more about these
                >items. incidently Don i do have some polarizers that i made years ago from
                >some sheet but obviously there is a lot more - and what a lot - to
                >polarization techniques than simple crossed polars.
                >
                Ian,

                At the risk of overloading a few more of your circuits, I have pasted
                below a description I posted last year on how to make a retardation
                plate from cellophane. Hope you (or someone else) finds it useful, and
                gets inspired to try it out.

                David


                If you are really hard up then experimenting with sheets of "cellophane"
                from product packaging (singly or folded) can give some fun results;
                though they will not - coincidence apart - give you a nice fraction of a
                wavelength of retardation, if you are not doing quantitative work the
                results can look pretty. See "Fundamentals of Light Microscopy and
                Electronic Imaging", by Douglas B Murphy, p 143.

                OK, here goes. Credit to Mr Murphy, as set out previously. I have
                however taken the liberty of paraphrasing and shortening a little.

                (1) Take a clear sheet of cellophane, such as that from a CD case and
                view (e.g. on a light box) between two crossed sheets of polaroid.
                Rotate the cellophane and note that there are 4 positions at which the
                cellophane appears clear against the crossed polars. Cellophane dialysis
                membranes are said to be good, but note that thick food-grade cellophane
                is too thick.

                (2) Note the angles at which this occurs, and mark with an X in felt-tip
                the azimuthal angles at 45 degrees to the principal axes of the polars
                (which if they have been cut correctly from a rectangular sheet will be
                along one of the straight edges).

                (3) Cut a rectangle from the cellophane so that its edges are parallel
                to the X you marked.

                (3A) [This step is optional, not part of the procedure, just to satisfy
                curiosity.] Fold the rectangle at 45 degrees from a corner. This will
                place the two layers at right angles to each other. Observe again
                between the crossed polars - the cellophane now remains black (or
                whatever the full extinction of your polars shows). This is because the
                retardation of one sheet of cellophane cancels out that of the other -
                the first slows the E rays relative to the O rays by a certain amount;
                in the second, because of the change of angle, the E and O directions
                are reversed and the "delayed" waves catch up.

                (4) Now back to the business. Unfold the 45 degree-folded rectangle and
                now fold it parallel to a pair of the edges (it doesn't matter which).
                View again between the crossed polars. With the rectangles edges at 45
                degrees to the axes of the polars, you should see a bright yellow
                colour. This is because the cellophane (assuming you chose a piece of
                the correct thickness) "has a retardation of about 230nm" (i.e.it has
                the combination of birefringence and thickness such that light of 230nm
                wavelength in air has the E ray retarded to be back in phase with the O
                ray - this means it is oriented exactly the same as the incident ray,
                which means it is extinguished by the analyser sheet of polaroid). This
                is of course way into the UV, but two such thicknesses takes the
                retardation to 460nm, well into the visible blue region. White light
                with a slice of blue cut out means the light is visible yellow.

                [Note this explains why a single sheet appears white under the polars -
                the extinction is way out of the visible region

                (4A) Out of interest, note that if you observe your new cellophane
                retardation plate with the polars aligned parallel, you should see a
                blue colour. I'll leave you to follow the logic of that...

                (5) As a final step, you may wish to determine the orientation of the
                index ellipsoid of your plate - note the crossed polars will only tell
                you that it is along one of the two arms of the X, but not which. For
                this you need a retarder of known index. If you have not got one, take a
                roll of cellophane tape (Sellotape or similar) - this is always made
                with the cellulose chains along its length; thus its slow axis is also
                parallel to the tape. Take two pieces of the tape on which you have
                drawn an ellipse in the appropriate direction (i.e. along the tape) -
                preferably before you cut them off so you don't lose track! Place one of
                these with its ellipse parallel to one pair of sides of your plate and
                one parallel to the other pair. Observe the whole sandwich again under
                crossed polars. The area with no sellotape will be yellow as before. The
                area with one of the pieces of tape will be blue; that with the other
                should be very pale yellow or white. The ellipse on the blue piece shows
                you the slow axis - the "index" - of your plate.

                [For the terminally curious, the retardation of the tape is added to the
                retardation of your plate when their index ellipsoids are parallel -
                thus 460 from your plate plus another 230 from the tape gives an
                extinction of 690 - in the yellow region of the spectrum. Where they
                are at right angles, the tape subtracts its retardation from that of
                your plate - 460 minus 230 gives an extinction of 230nm, in the
                ultra-violet, but because of various variables is likely to spread into
                the deep blue region, leaving a faint yellow.]

                I very strongly recommend anyone interested in this area to give it a
                try - it's great fun, it costs nothing and you end up with a calibrated
                retardation plate. If you want, you can mount it in a filter holder with
                the index marked, or do all sorts of other fun things.

                I also recommend the book - it has probably the best explanation of how
                this stuff works of any I have seen. I must confess I sometimes get it
                tangled in my mind and have to go back to get it straight, and this is
                the best book for that!

                Hope this helps,
                --
                David Littlewood
              • D. Halterman
                Hi, Polarization is everywhere. Here s a really simple experiment anyone can do. Put on a pair of poalrized sunglasses. Sit in your car and look out of the
                Message 7 of 23 , Nov 1, 2005
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                  Hi,

                  Polarization is everywhere. Here's a really simple
                  experiment anyone can do. Put on a pair of poalrized
                  sunglasses. Sit in your car and look out of the
                  windshield. Tilt your head to the left and right.
                  See how the windshield glare appears and disappears.
                  Now sit up straight and look at the car clock or radio
                  panel, or the dashboard. Now tilt your head. If any
                  of these have LCD panels especially, you will see them
                  darken or even turn black.

                  What is happening is that the polarization in the
                  windshield and the stretched plastic accessory covers
                  are aligned so that you can see through them when
                  wearing polarized sunglasses.

                  Don



                  --- David Littlewood <david@...> wrote:

                  > In message
                  > <DJENLJHAKHOJPNAFDNOKCEOLDAAA.kenchy475@...>,
                  > kenchy475
                  > <kenchy475@...> writes
                  > >thanks for the info and links Don and thanks for
                  > the extra input David re
                  > >the Quekett - its all a bit clearer now and
                  > certainly the ebay item has now
                  > >sprung to life instead of being just a piece of
                  > flat metal with what
                  > >appeared to be a hole in it -




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                • Dave Martindale
                  I recently acquired an American Optical (later Reichert) Forty stereo microscope. It s a model 42, with 10X and 20X magnification. It s built like a tank
                  Message 8 of 23 , Nov 1, 2005
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                    I recently acquired an American Optical (later Reichert) Forty stereo
                    microscope. It's a model 42, with 10X and 20X magnification. It's
                    built like a tank mechanically, and still seems to be in good condition
                    optically.

                    When I got it, it was capable of reflective illumination only. An
                    opaque black/white stage plate was glued in place on the microscope base
                    with the black side up. I want to get the transmissive illumination
                    system working too, and I've successfully "unglued" the opaque plate
                    from the base. Now the hole in the stage is accessible.

                    I found the original manual for the AO 40 in one of the archives
                    connected to this list (an invaluable resource), including a exploded
                    parts diagram, so I know what parts originally made up the reflective
                    illumination system. All the electrical stuff is already there: the
                    second switch, the bulb socket, and interconnection wiring. I've found
                    a suitable bulb. But there's no stage glass, seal, reflector assembly,
                    or shield deflector (to use the terminology of the manual), nor any sign
                    that some of them were once present.

                    My best guess is that perhaps AO installed full reflective/transmissive
                    wiring on all of their microscopes, but that this particular one was
                    sold as a reflective-only model with the opaque stage plate installed.
                    Somewhere along the line, someone damaged that stage plate, so they
                    removed and discarded it, and glued a larger-diameter plate on top of
                    the base, covering the hole. And that's how it was when I got it.

                    I figure I can probably make a new transparent stage plate from Lexan.
                    Glass is not practical because the plate needs a bevelled edge to fit
                    the bevelled opening in the base, and I can probably machine Lexan but
                    not glass. The "reflector assembly" looks like stamped metal, but a
                    round aluminum disc with a hole in the centre should serve to hold the
                    stage plate. The reflector itself and the "shield deflector" look like
                    they could be made from sheet metal, cut and bent.

                    Finally, to my questions: What was the "stage glass" made of in AO 40
                    units equipped by the factory for transmissive illumination? Was it
                    opal glass to provide some diffusion? Or was it clear glass? If the
                    latter, is there anything else to diffuse the light mounted between bulb
                    and stage plate? Photos of the microscope make it look like the light
                    is diffused somehow, but the parts diagram shows no separate device for
                    that.

                    Dave
                  • D. Halterman
                    Maybe I m misunderstanding your configuration, and pardon me if I am; but if you want to make a reflector out of metal, you should get yourself some specular
                    Message 9 of 23 , Nov 1, 2005
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                      Maybe I'm misunderstanding your configuration, and
                      pardon me if I am; but if you want to make a reflector
                      out of metal, you should get yourself some specular
                      aluminum sheeting; or, you can purchase a
                      first-surface aluminum mirror from Edumnd Scientific.

                      Hope this helps,
                      Don



                      --- Dave Martindale <dave.martindale@...> wrote:

                      > I recently acquired an American Optical (later
                      > Reichert) Forty stereo
                      > microscope. It's a model 42, with 10X and 20X
                      > magnification. It's
                      > built like a tank mechanically, and still seems to
                      > be in good condition
                      > optically.
                      >



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                      Yahoo! FareChase: Search multiple travel sites in one click.
                      http://farechase.yahoo.com
                    • David Littlewood
                      In message , Dave Martindale writes ... I have two stereo microscopes. The Zeiss has a clear glass plate,
                      Message 10 of 23 , Nov 2, 2005
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                        In message <4368501D.5030805@...>, Dave Martindale
                        <dave.martindale@...> writes
                        >I recently acquired an American Optical (later Reichert) Forty stereo
                        >microscope. It's a model 42, with 10X and 20X magnification. It's
                        >built like a tank mechanically, and still seems to be in good condition
                        >optically.
                        >
                        >When I got it, it was capable of reflective illumination only. An
                        >opaque black/white stage plate was glued in place on the microscope base
                        >with the black side up. I want to get the transmissive illumination
                        >system working too, and I've successfully "unglued" the opaque plate
                        >from the base. Now the hole in the stage is accessible.
                        >
                        >I found the original manual for the AO 40 in one of the archives
                        >connected to this list (an invaluable resource), including a exploded
                        >parts diagram, so I know what parts originally made up the reflective
                        >illumination system. All the electrical stuff is already there: the
                        >second switch, the bulb socket, and interconnection wiring. I've found
                        >a suitable bulb. But there's no stage glass, seal, reflector assembly,
                        >or shield deflector (to use the terminology of the manual), nor any sign
                        >that some of them were once present.
                        >
                        >My best guess is that perhaps AO installed full reflective/transmissive
                        >wiring on all of their microscopes, but that this particular one was
                        >sold as a reflective-only model with the opaque stage plate installed.
                        >Somewhere along the line, someone damaged that stage plate, so they
                        >removed and discarded it, and glued a larger-diameter plate on top of
                        >the base, covering the hole. And that's how it was when I got it.
                        >
                        >I figure I can probably make a new transparent stage plate from Lexan.
                        >Glass is not practical because the plate needs a bevelled edge to fit
                        >the bevelled opening in the base, and I can probably machine Lexan but
                        >not glass. The "reflector assembly" looks like stamped metal, but a
                        >round aluminum disc with a hole in the centre should serve to hold the
                        >stage plate. The reflector itself and the "shield deflector" look like
                        >they could be made from sheet metal, cut and bent.
                        >
                        >Finally, to my questions: What was the "stage glass" made of in AO 40
                        >units equipped by the factory for transmissive illumination? Was it
                        >opal glass to provide some diffusion? Or was it clear glass? If the
                        >latter, is there anything else to diffuse the light mounted between bulb
                        >and stage plate? Photos of the microscope make it look like the light
                        >is diffused somehow, but the parts diagram shows no separate device for
                        >that.
                        >
                        > Dave
                        >
                        I have two stereo microscopes. The Zeiss has a clear glass plate, and
                        the Russian one has a frosted glass plate. I guess the difference is
                        that the Zeiss has a pair of Kohler lamps (yes, a pair, in a Y- one for
                        each tube!) whereas the Russian has a plain bulb illuminator.

                        From your description, it seems your AO has a plain bulb illuminator, so
                        I would guess that frosted glass would be preferred. But I have no
                        direct knowledge of the AO scopes, so it's only a guess.

                        David
                        --
                        David Littlewood
                      • kenchy475
                        thanks David this is just the sort of thing that i like to mess with - something inexpensive a bit of fun and simultaneously educational [maybe santa will
                        Message 11 of 23 , Nov 2, 2005
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                          thanks David this is just the sort of thing that i like to mess with -
                          something inexpensive a bit of fun and simultaneously educational [maybe
                          santa will bring the book - hes got loads of money lol!]
                          Ian

                          -----Original Message-----
                          From: Microscope@yahoogroups.com [mailto:Microscope@yahoogroups.com]On
                          Behalf Of David Littlewood
                          Sent: 01 November 2005 23:25
                          To: microscope@yahoogroups.com
                          Subject: Re: [Microscope] Re: Leitz Wetzlar Wedge for Microscope


                          In message <DJENLJHAKHOJPNAFDNOKCEOLDAAA.kenchy475@...>, kenchy475
                          <kenchy475@...> writes
                          >thanks for the info and links Don and thanks for the extra input David re
                          >the Quekett - its all a bit clearer now and certainly the ebay item has now
                          >sprung to life instead of being just a piece of flat metal with what
                          >appeared to be a hole in it - i can relate it to my scopes now - dont know
                          >if i'll get the time to make up anything at the mo but i will keep my eye
                          >out for any bits that may come my way now that i know a bit more about
                          these
                          >items. incidently Don i do have some polarizers that i made years ago from
                          >some sheet but obviously there is a lot more - and what a lot - to
                          >polarization techniques than simple crossed polars.
                          >
                          Ian,

                          At the risk of overloading a few more of your circuits, I have pasted
                          below a description I posted last year on how to make a retardation
                          plate from cellophane. Hope you (or someone else) finds it useful, and
                          gets inspired to try it out.

                          David


                          If you are really hard up then experimenting with sheets of "cellophane"
                          from product packaging (singly or folded) can give some fun results;
                          though they will not - coincidence apart - give you a nice fraction of a
                          wavelength of retardation, if you are not doing quantitative work the
                          results can look pretty. See "Fundamentals of Light Microscopy and
                          Electronic Imaging", by Douglas B Murphy, p 143.

                          OK, here goes. Credit to Mr Murphy, as set out previously. I have
                          however taken the liberty of paraphrasing and shortening a little.

                          (1) Take a clear sheet of cellophane, such as that from a CD case and
                          view (e.g. on a light box) between two crossed sheets of polaroid.
                          Rotate the cellophane and note that there are 4 positions at which the
                          cellophane appears clear against the crossed polars. Cellophane dialysis
                          membranes are said to be good, but note that thick food-grade cellophane
                          is too thick.

                          (2) Note the angles at which this occurs, and mark with an X in felt-tip
                          the azimuthal angles at 45 degrees to the principal axes of the polars
                          (which if they have been cut correctly from a rectangular sheet will be
                          along one of the straight edges).

                          (3) Cut a rectangle from the cellophane so that its edges are parallel
                          to the X you marked.

                          (3A) [This step is optional, not part of the procedure, just to satisfy
                          curiosity.] Fold the rectangle at 45 degrees from a corner. This will
                          place the two layers at right angles to each other. Observe again
                          between the crossed polars - the cellophane now remains black (or
                          whatever the full extinction of your polars shows). This is because the
                          retardation of one sheet of cellophane cancels out that of the other -
                          the first slows the E rays relative to the O rays by a certain amount;
                          in the second, because of the change of angle, the E and O directions
                          are reversed and the "delayed" waves catch up.

                          (4) Now back to the business. Unfold the 45 degree-folded rectangle and
                          now fold it parallel to a pair of the edges (it doesn't matter which).
                          View again between the crossed polars. With the rectangles edges at 45
                          degrees to the axes of the polars, you should see a bright yellow
                          colour. This is because the cellophane (assuming you chose a piece of
                          the correct thickness) "has a retardation of about 230nm" (i.e.it has
                          the combination of birefringence and thickness such that light of 230nm
                          wavelength in air has the E ray retarded to be back in phase with the O
                          ray - this means it is oriented exactly the same as the incident ray,
                          which means it is extinguished by the analyser sheet of polaroid). This
                          is of course way into the UV, but two such thicknesses takes the
                          retardation to 460nm, well into the visible blue region. White light
                          with a slice of blue cut out means the light is visible yellow.

                          [Note this explains why a single sheet appears white under the polars -
                          the extinction is way out of the visible region

                          (4A) Out of interest, note that if you observe your new cellophane
                          retardation plate with the polars aligned parallel, you should see a
                          blue colour. I'll leave you to follow the logic of that...

                          (5) As a final step, you may wish to determine the orientation of the
                          index ellipsoid of your plate - note the crossed polars will only tell
                          you that it is along one of the two arms of the X, but not which. For
                          this you need a retarder of known index. If you have not got one, take a
                          roll of cellophane tape (Sellotape or similar) - this is always made
                          with the cellulose chains along its length; thus its slow axis is also
                          parallel to the tape. Take two pieces of the tape on which you have
                          drawn an ellipse in the appropriate direction (i.e. along the tape) -
                          preferably before you cut them off so you don't lose track! Place one of
                          these with its ellipse parallel to one pair of sides of your plate and
                          one parallel to the other pair. Observe the whole sandwich again under
                          crossed polars. The area with no sellotape will be yellow as before. The
                          area with one of the pieces of tape will be blue; that with the other
                          should be very pale yellow or white. The ellipse on the blue piece shows
                          you the slow axis - the "index" - of your plate.

                          [For the terminally curious, the retardation of the tape is added to the
                          retardation of your plate when their index ellipsoids are parallel -
                          thus 460 from your plate plus another 230 from the tape gives an
                          extinction of 690 - in the yellow region of the spectrum. Where they
                          are at right angles, the tape subtracts its retardation from that of
                          your plate - 460 minus 230 gives an extinction of 230nm, in the
                          ultra-violet, but because of various variables is likely to spread into
                          the deep blue region, leaving a faint yellow.]

                          I very strongly recommend anyone interested in this area to give it a
                          try - it's great fun, it costs nothing and you end up with a calibrated
                          retardation plate. If you want, you can mount it in a filter holder with
                          the index marked, or do all sorts of other fun things.

                          I also recommend the book - it has probably the best explanation of how
                          this stuff works of any I have seen. I must confess I sometimes get it
                          tangled in my mind and have to go back to get it straight, and this is
                          the best book for that!

                          Hope this helps,
                          --
                          David Littlewood





                          Yahoo! Groups Links
                        • Salvatore Previtera
                          Hi David, quite a good and precise explanation. With some care and patience it is possible by examining several samples of cellophane and other plastic films
                          Message 12 of 23 , Nov 2, 2005
                          • 0 Attachment
                            Hi David,
                            quite a good and precise explanation.
                            With some care and patience it is possible by examining several samples of
                            cellophane and other plastic films so diffuse today to make preparates of
                            various retardation including lambda/4 and lambda/2, and a stepped wedge.
                            I can add only, as I already said before, the usage of polymethyl
                            metacrylate (PMMA, lucite or plexiglas) stretched at 100° to get a continous
                            wedge.
                            Regards,
                            Salvatore

                            ----- Original Message -----
                            From: "David Littlewood" <david@...>
                            To: <microscope@yahoogroups.com>
                            Sent: Wednesday, November 02, 2005 12:25 AM
                            Subject: Re: [Microscope] Re: Leitz Wetzlar Wedge for Microscope


                            > In message <DJENLJHAKHOJPNAFDNOKCEOLDAAA.kenchy475@...>, kenchy475
                            > <kenchy475@...> writes
                            > >thanks for the info and links Don and thanks for the extra input David re
                            > >the Quekett - its all a bit clearer now and certainly the ebay item has
                            now
                            > >sprung to life instead of being just a piece of flat metal with what
                            > >appeared to be a hole in it - i can relate it to my scopes now - dont
                            know
                            > >if i'll get the time to make up anything at the mo but i will keep my eye
                            > >out for any bits that may come my way now that i know a bit more about
                            these
                            > >items. incidently Don i do have some polarizers that i made years ago
                            from
                            > >some sheet but obviously there is a lot more - and what a lot - to
                            > >polarization techniques than simple crossed polars.
                            > >
                            > Ian,
                            >
                            > At the risk of overloading a few more of your circuits, I have pasted
                            > below a description I posted last year on how to make a retardation
                            > plate from cellophane. Hope you (or someone else) finds it useful, and
                            > gets inspired to try it out.
                            >
                            > David
                            >
                            >
                            > If you are really hard up then experimenting with sheets of "cellophane"
                            > from product packaging (singly or folded) can give some fun results;
                            > though they will not - coincidence apart - give you a nice fraction of a
                            > wavelength of retardation, if you are not doing quantitative work the
                            > results can look pretty. See "Fundamentals of Light Microscopy and
                            > Electronic Imaging", by Douglas B Murphy, p 143.
                            >
                            > OK, here goes. Credit to Mr Murphy, as set out previously. I have
                            > however taken the liberty of paraphrasing and shortening a little.
                            >
                            > (1) Take a clear sheet of cellophane, such as that from a CD case and
                            > view (e.g. on a light box) between two crossed sheets of polaroid.
                            > Rotate the cellophane and note that there are 4 positions at which the
                            > cellophane appears clear against the crossed polars. Cellophane dialysis
                            > membranes are said to be good, but note that thick food-grade cellophane
                            > is too thick.
                            >
                            > (2) Note the angles at which this occurs, and mark with an X in felt-tip
                            > the azimuthal angles at 45 degrees to the principal axes of the polars
                            > (which if they have been cut correctly from a rectangular sheet will be
                            > along one of the straight edges).
                            >
                            > (3) Cut a rectangle from the cellophane so that its edges are parallel
                            > to the X you marked.
                            >
                            > (3A) [This step is optional, not part of the procedure, just to satisfy
                            > curiosity.] Fold the rectangle at 45 degrees from a corner. This will
                            > place the two layers at right angles to each other. Observe again
                            > between the crossed polars - the cellophane now remains black (or
                            > whatever the full extinction of your polars shows). This is because the
                            > retardation of one sheet of cellophane cancels out that of the other -
                            > the first slows the E rays relative to the O rays by a certain amount;
                            > in the second, because of the change of angle, the E and O directions
                            > are reversed and the "delayed" waves catch up.
                            >
                            > (4) Now back to the business. Unfold the 45 degree-folded rectangle and
                            > now fold it parallel to a pair of the edges (it doesn't matter which).
                            > View again between the crossed polars. With the rectangles edges at 45
                            > degrees to the axes of the polars, you should see a bright yellow
                            > colour. This is because the cellophane (assuming you chose a piece of
                            > the correct thickness) "has a retardation of about 230nm" (i.e.it has
                            > the combination of birefringence and thickness such that light of 230nm
                            > wavelength in air has the E ray retarded to be back in phase with the O
                            > ray - this means it is oriented exactly the same as the incident ray,
                            > which means it is extinguished by the analyser sheet of polaroid). This
                            > is of course way into the UV, but two such thicknesses takes the
                            > retardation to 460nm, well into the visible blue region. White light
                            > with a slice of blue cut out means the light is visible yellow.
                            >
                            > [Note this explains why a single sheet appears white under the polars -
                            > the extinction is way out of the visible region
                            >
                            > (4A) Out of interest, note that if you observe your new cellophane
                            > retardation plate with the polars aligned parallel, you should see a
                            > blue colour. I'll leave you to follow the logic of that...
                            >
                            > (5) As a final step, you may wish to determine the orientation of the
                            > index ellipsoid of your plate - note the crossed polars will only tell
                            > you that it is along one of the two arms of the X, but not which. For
                            > this you need a retarder of known index. If you have not got one, take a
                            > roll of cellophane tape (Sellotape or similar) - this is always made
                            > with the cellulose chains along its length; thus its slow axis is also
                            > parallel to the tape. Take two pieces of the tape on which you have
                            > drawn an ellipse in the appropriate direction (i.e. along the tape) -
                            > preferably before you cut them off so you don't lose track! Place one of
                            > these with its ellipse parallel to one pair of sides of your plate and
                            > one parallel to the other pair. Observe the whole sandwich again under
                            > crossed polars. The area with no sellotape will be yellow as before. The
                            > area with one of the pieces of tape will be blue; that with the other
                            > should be very pale yellow or white. The ellipse on the blue piece shows
                            > you the slow axis - the "index" - of your plate.
                            >
                            > [For the terminally curious, the retardation of the tape is added to the
                            > retardation of your plate when their index ellipsoids are parallel -
                            > thus 460 from your plate plus another 230 from the tape gives an
                            > extinction of 690 - in the yellow region of the spectrum. Where they
                            > are at right angles, the tape subtracts its retardation from that of
                            > your plate - 460 minus 230 gives an extinction of 230nm, in the
                            > ultra-violet, but because of various variables is likely to spread into
                            > the deep blue region, leaving a faint yellow.]
                            >
                            > I very strongly recommend anyone interested in this area to give it a
                            > try - it's great fun, it costs nothing and you end up with a calibrated
                            > retardation plate. If you want, you can mount it in a filter holder with
                            > the index marked, or do all sorts of other fun things.
                            >
                            > I also recommend the book - it has probably the best explanation of how
                            > this stuff works of any I have seen. I must confess I sometimes get it
                            > tangled in my mind and have to go back to get it straight, and this is
                            > the best book for that!
                            >
                            > Hope this helps,
                            > --
                            > David Littlewood
                            >
                            >
                            >
                            >
                            >
                            > Yahoo! Groups Links
                            >
                            >
                            >
                            >
                            >
                            >
                          • Steve Neeley
                            A version of the manual and catalog can be found at: http://www.xmission.com/~psneeley/Personal/Microscope.htm FWIW, Steve ... stereo ... It s ... condition
                            Message 13 of 23 , Nov 2, 2005
                            • 0 Attachment
                              A version of the manual and catalog can be found at:

                              http://www.xmission.com/~psneeley/Personal/Microscope.htm

                              FWIW,

                              Steve


                              --- In Microscope@yahoogroups.com, David Littlewood <david@d...>
                              wrote:
                              >
                              > In message <4368501D.5030805@s...>, Dave Martindale
                              > <dave.martindale@s...> writes
                              > >I recently acquired an American Optical (later Reichert) Forty
                              stereo
                              > >microscope. It's a model 42, with 10X and 20X magnification.
                              It's
                              > >built like a tank mechanically, and still seems to be in good
                              condition
                              > >optically.
                              > >
                              > >When I got it, it was capable of reflective illumination only. An
                              > >opaque black/white stage plate was glued in place on the
                              microscope base
                              > >with the black side up. I want to get the transmissive
                              illumination
                              > >system working too, and I've successfully "unglued" the opaque
                              plate
                              > >from the base. Now the hole in the stage is accessible.
                              > >
                              > >I found the original manual for the AO 40 in one of the archives
                              > >connected to this list (an invaluable resource), including a
                              exploded
                              > >parts diagram, so I know what parts originally made up the
                              reflective
                              > >illumination system. All the electrical stuff is already there:
                              the
                              > >second switch, the bulb socket, and interconnection wiring. I've
                              found
                              > >a suitable bulb. But there's no stage glass, seal, reflector
                              assembly,
                              > >or shield deflector (to use the terminology of the manual), nor
                              any sign
                              > >that some of them were once present.
                              > >
                              > >My best guess is that perhaps AO installed full
                              reflective/transmissive
                              > >wiring on all of their microscopes, but that this particular one
                              was
                              > >sold as a reflective-only model with the opaque stage plate
                              installed.
                              > >Somewhere along the line, someone damaged that stage plate, so
                              they
                              > >removed and discarded it, and glued a larger-diameter plate on
                              top of
                              > >the base, covering the hole. And that's how it was when I got it.
                              > >
                              > >I figure I can probably make a new transparent stage plate from
                              Lexan.
                              > >Glass is not practical because the plate needs a bevelled edge to
                              fit
                              > >the bevelled opening in the base, and I can probably machine
                              Lexan but
                              > >not glass. The "reflector assembly" looks like stamped metal,
                              but a
                              > >round aluminum disc with a hole in the centre should serve to
                              hold the
                              > >stage plate. The reflector itself and the "shield deflector"
                              look like
                              > >they could be made from sheet metal, cut and bent.
                              > >
                              > >Finally, to my questions: What was the "stage glass" made of in
                              AO 40
                              > >units equipped by the factory for transmissive illumination? Was
                              it
                              > >opal glass to provide some diffusion? Or was it clear glass? If
                              the
                              > >latter, is there anything else to diffuse the light mounted
                              between bulb
                              > >and stage plate? Photos of the microscope make it look like the
                              light
                              > >is diffused somehow, but the parts diagram shows no separate
                              device for
                              > >that.
                              > >
                              > > Dave
                              > >
                              > I have two stereo microscopes. The Zeiss has a clear glass plate,
                              and
                              > the Russian one has a frosted glass plate. I guess the difference
                              is
                              > that the Zeiss has a pair of Kohler lamps (yes, a pair, in a Y-
                              one for
                              > each tube!) whereas the Russian has a plain bulb illuminator.
                              >
                              > From your description, it seems your AO has a plain bulb
                              illuminator, so
                              > I would guess that frosted glass would be preferred. But I have no
                              > direct knowledge of the AO scopes, so it's only a guess.
                              >
                              > David
                              > --
                              > David Littlewood
                              >
                            • David Sykes
                              ... Well, it s worth quite a lot :-) As mentioned on your website, I would appreciate the Reichert and AO manuals for the StereoStar. Thanks, David Sykes
                              Message 14 of 23 , Nov 2, 2005
                              • 0 Attachment
                                Steve Neeley wrote:

                                > A version of the manual and catalog can be found at:
                                > http://www.xmission.com/~psneeley/Personal/Microscope.htm
                                > FWIW

                                Well, it's worth quite a lot :-)

                                As mentioned on your website, I would appreciate the Reichert and AO
                                manuals for the StereoStar.

                                Thanks,


                                David Sykes
                              • Aaron
                                If you send me the diameter of the hole I think I have an OEM glass replacement. Aaron ... stereo ... It s ... condition ... microscope base ... illumination
                                Message 15 of 23 , Nov 2, 2005
                                • 0 Attachment
                                  If you send me the diameter of the hole I think I have an OEM glass
                                  replacement.

                                  Aaron

                                  --- In Microscope@yahoogroups.com, Dave Martindale
                                  <dave.martindale@s...> wrote:
                                  >
                                  > I recently acquired an American Optical (later Reichert) Forty
                                  stereo
                                  > microscope. It's a model 42, with 10X and 20X magnification.
                                  It's
                                  > built like a tank mechanically, and still seems to be in good
                                  condition
                                  > optically.
                                  >
                                  > When I got it, it was capable of reflective illumination only. An
                                  > opaque black/white stage plate was glued in place on the
                                  microscope base
                                  > with the black side up. I want to get the transmissive
                                  illumination
                                  > system working too, and I've successfully "unglued" the opaque
                                  plate
                                  > from the base. Now the hole in the stage is accessible.
                                  >
                                  > I found the original manual for the AO 40 in one of the archives
                                  > connected to this list (an invaluable resource), including a
                                  exploded
                                  > parts diagram, so I know what parts originally made up the
                                  reflective
                                  > illumination system. All the electrical stuff is already there:
                                  the
                                  > second switch, the bulb socket, and interconnection wiring. I've
                                  found
                                  > a suitable bulb. But there's no stage glass, seal, reflector
                                  assembly,
                                  > or shield deflector (to use the terminology of the manual), nor
                                  any sign
                                  > that some of them were once present.
                                  >
                                  > My best guess is that perhaps AO installed full
                                  reflective/transmissive
                                  > wiring on all of their microscopes, but that this particular one
                                  was
                                  > sold as a reflective-only model with the opaque stage plate
                                  installed.
                                  > Somewhere along the line, someone damaged that stage plate, so
                                  they
                                  > removed and discarded it, and glued a larger-diameter plate on top
                                  of
                                  > the base, covering the hole. And that's how it was when I got it.
                                  >
                                  > I figure I can probably make a new transparent stage plate from
                                  Lexan.
                                  > Glass is not practical because the plate needs a bevelled edge to
                                  fit
                                  > the bevelled opening in the base, and I can probably machine Lexan
                                  but
                                  > not glass. The "reflector assembly" looks like stamped metal, but
                                  a
                                  > round aluminum disc with a hole in the centre should serve to hold
                                  the
                                  > stage plate. The reflector itself and the "shield deflector" look
                                  like
                                  > they could be made from sheet metal, cut and bent.
                                  >
                                  > Finally, to my questions: What was the "stage glass" made of in AO
                                  40
                                  > units equipped by the factory for transmissive illumination? Was
                                  it
                                  > opal glass to provide some diffusion? Or was it clear glass? If
                                  the
                                  > latter, is there anything else to diffuse the light mounted
                                  between bulb
                                  > and stage plate? Photos of the microscope make it look like the
                                  light
                                  > is diffused somehow, but the parts diagram shows no separate
                                  device for
                                  > that.
                                  >
                                  > Dave
                                  >
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