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Re: Colour coding on the aberration graph

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  • Timm Bottoni
    Good question Dmitri! I want to know more than that, I also want someone to explain how to read it and what it really means. I want to be able to add this to
    Message 1 of 7 , Jan 23, 2006
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      Good question Dmitri!

      I want to know more than that, I also want someone to explain how to
      read it and what it really means.

      I want to be able to add this to the FAQs I am working on for the
      group, as well as for my own understanding.

      I actually went out and downloaded the Zemax demo, but even after
      reading and understanding the basics, and searching Google, I still
      don't understand what the charts mean, to be honest, and how to use
      them to compare one scope to another.

      The real software costs $2000-$4000 and then you have to pay for
      training, so maybe this is one of those things that you can't learn
      for free, but lets see if anyone has an explanation in our group.

      Anyone? Tom? Ron? Anyone feel free to offer to explain these.

      Also - Tom Trusak has posted his opinions and thoughts on doublets
      vs. triplets, and I will try to includes some of that in the FAQs
      since it comes up often as well. I have a few sites that are very
      technical, but if anyone has an easy web site that helps explain it
      feel free to post it.

      The majjority of companies do NOT post these types of charts, or the
      glass specs, or the color correction levels, or quality control
      specifications. Perhaps WO is just more honest, or perhaps they feel
      that the charts help people, or perhaps other companies just don't
      want to open the kimono that far because it lets competitors see what
      they are doing, and gives them a chance to try to one-up them with a
      better looking chart.

      Either way - if anyone has any information, let us all know.

      Timm

      --- In William-Optics@yahoogroups.com, "kulginoff"
      <dmitri.kulginov@e...> wrote:
      >
      > I would like to know the colour legend on the chromatic aberration
      > graph for Zenith Star Fluorite Doublet on the WO web site,
      >
      > http://www.william-optics.com/wowebs/prod_tel/zsfd80/chrom.htm
      >
      > Thankfully,
      > Dmitri
      >
    • clivegibbonsca
      ... to ... the ... feel ... what ... a ... FWIW, I asked William Optics this question late last year. They sent me the legend for the color correction graph.
      Message 2 of 7 , Jan 23, 2006
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        --- In William-Optics@yahoogroups.com, "Timm Bottoni"
        <t.bottoni@c...> wrote:
        >
        > Good question Dmitri!
        >
        > I want to know more than that, I also want someone to explain how
        to
        > read it and what it really means.
        >
        > I want to be able to add this to the FAQs I am working on for the
        > group, as well as for my own understanding.
        >
        > I actually went out and downloaded the Zemax demo, but even after
        > reading and understanding the basics, and searching Google, I still
        > don't understand what the charts mean, to be honest, and how to use
        > them to compare one scope to another.
        >
        > The real software costs $2000-$4000 and then you have to pay for
        > training, so maybe this is one of those things that you can't learn
        > for free, but lets see if anyone has an explanation in our group.
        >
        > Anyone? Tom? Ron? Anyone feel free to offer to explain these.
        >
        > Also - Tom Trusak has posted his opinions and thoughts on doublets
        > vs. triplets, and I will try to includes some of that in the FAQs
        > since it comes up often as well. I have a few sites that are very
        > technical, but if anyone has an easy web site that helps explain it
        > feel free to post it.
        >
        > The majjority of companies do NOT post these types of charts, or
        the
        > glass specs, or the color correction levels, or quality control
        > specifications. Perhaps WO is just more honest, or perhaps they
        feel
        > that the charts help people, or perhaps other companies just don't
        > want to open the kimono that far because it lets competitors see
        what
        > they are doing, and gives them a chance to try to one-up them with
        a
        > better looking chart.
        >
        > Either way - if anyone has any information, let us all know.
        >
        > Timm
        >
        > --- In William-Optics@yahoogroups.com, "kulginoff"
        > <dmitri.kulginov@e...> wrote:
        > >
        > > I would like to know the colour legend on the chromatic aberration
        > > graph for Zenith Star Fluorite Doublet on the WO web site,
        > >
        > > http://www.william-optics.com/wowebs/prod_tel/zsfd80/chrom.htm
        > >
        > > Thankfully,
        > > Dmitri
        > >
        >

        FWIW, I asked William Optics this question late last year.
        They sent me the legend for the color correction graph.
        I've uploaded it to the Files section:
        WO80FD.jpg

        Hope this helps!


        Clive.
      • kulginoff
        Clive, thanks! Dmitri
        Message 3 of 7 , Jan 23, 2006
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          Clive, thanks!

          Dmitri
        • Craig Stark
          OK, so here is what I believe it means. I am no expert, but I did look into this a bit some time ago. FWIW, this page may help explain the issues:
          Message 4 of 7 , Jan 23, 2006
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            OK, so here is what I believe it means. I am no expert, but I did
            look into this a bit some time ago. FWIW, this page may help explain
            the issues:
            http://www.vanwalree.com/optics/chromatic.html

            The "Longitudinal Aberration" is showing the distance between focal
            planes for light of varying wavelengths. Red light focuses in a
            different place that blue light. As we visually focus on green (where
            we are most sensitive), the shift in focal planes for different freqs
            of light "blur" those freqs and lead to things like color halos.

            So, what this graph is showing is for different frequencies (I think
            we can safely ignore the 435 and 707nm) how far off focus are we? If
            we find the spot where they cluster the most (about the third tick
            from the top) and say that we have our focuser at this position
            (y-axis here is focal plane position), we can see that we have a nice
            clustering. Ignore the dark blue and the dark red (getting pretty UV
            and IR) and the focal plane shift for a nice cluster in there save the
            ~656 (Ha-like line) is on the order of .05mm.

            Craig
          • Scott Walker
            Someone has already answered the color question. I thought I would answer your question on what the graph means. The graph shows how different wavelengths
            Message 5 of 7 , Jan 23, 2006
            • 0 Attachment
              Someone has already answered the color question. I thought I would answer your question on what the graph means. The graph shows how different wavelengths focus as a function of lens radial position. The bottom of the y axis is the center of the lens. The top is the outer diameter. Restated this graph shows the spherical aberration of the lens at different colors and chromatic aberration. The eye is most sensitive to light around 550nmeter, so the graphs should be about a straight line at this wavelength in a well designed lens. The graph for the Fluorite Doublet shows the lens to be very well corrected at all but the wavelength extremes. At 435nmeters the focus point is about .125mm from the 550nmeter point. (typically the focus position is calculated at 70% of full aperture). This shift in focus will cause a blur diameter of about .02mm (.125/f-stop). So at 435nm the blur is much larger than due to diffraction(around .008mm). For visual use this is of little concern because the eye has very little sensitivity at this wavelength. One of the questions floating around has been what is the difference between an APO doublet and an APO triplet. WO address this question with the longitudinal aberration chart shown in Megrez 80 fluorite triplet. It shows the curves for a doublet and a triplet. In general the triplet can bring the focus points a the 70% of max radius, much closer together over the full visual range. Also look at the curves for the Megrez 80 II ED triplet APO. Even though it uses a lesser glass than the fluorite doublet, the color correction at the extremes is much better. The comparison between a triplet and a doublet is also shown on the WO website in the 66 ED APO section. Here spot diameters are shown. As one can see the spot diameters are much small at the wavelength extremes for the triplet. The photographic process tends to be more sensitive to the color extremes. This is why triplet are often preferred for photographic work. I hope this helps.
               
              Scott
               
               
              ----- Original Message -----
              Sent: Monday, January 23, 2006 7:19 AM
              Subject: [William-Optics] Re: Colour coding on the aberration graph

              Good question Dmitri!

              I want to know more than that, I also want someone to explain how to
              read it and what it really means.

              I want to be able to add this to the FAQs I am working on for the
              group, as well as for my own understanding.

              I actually went out and downloaded the Zemax demo, but even after
              reading and understanding the basics, and searching Google, I still
              don't understand what the charts mean, to be honest, and how to use
              them to compare one scope to another.

              The real software costs $2000-$4000 and then you have to pay for
              training, so maybe this is one of those things that you can't learn
              for free, but lets see if anyone has an explanation in our group.

              Anyone?  Tom?  Ron?  Anyone feel free to offer to explain these.

              Also - Tom Trusak has posted his opinions and thoughts on doublets
              vs. triplets, and I will try to includes some of that in the FAQs
              since it comes up often as well.  I have a few sites that are very
              technical, but if anyone has an easy web site that helps explain it
              feel free to post it.

              The majjority of companies do NOT post these types of charts, or the
              glass specs, or the color correction levels, or quality control
              specifications.  Perhaps WO is just more honest, or perhaps they feel
              that the charts help people, or perhaps other companies just don't
              want to open the kimono that far because it lets competitors see what
              they are doing, and gives them a chance to try to one-up them with a
              better looking chart.

              Either way - if anyone has any information, let us all know.

              Timm

              --- In William-Optics@yahoogroups.com, "kulginoff"
              <dmitri.kulginov@e...> wrote:
              >
              > I would like to know the colour legend on the chromatic aberration
              > graph for Zenith Star Fluorite Doublet on the WO web site,
              >
              > http://www.william-optics.com/wowebs/prod_tel/zsfd80/chrom.htm
              >
              > Thankfully,
              > Dmitri
              >





            • Timm Bottoni
              Thanks Scott, It does help - I will have to read it a few times over while looking at the charts when i am not at work, and being interupted by other less
              Message 6 of 7 , Jan 23, 2006
              • 0 Attachment
                Thanks Scott,

                It does help - I will have to read it a few times over while looking
                at the charts when i am not at work, and being interupted by other
                less important topics to fully grasp it ;-)

                Do you know of any web sites that explain it?

                I have Googled a number of times on things like "longitudinal
                chromatic aberration", but never really found anything that would
                explain those charts, so perhaps there aren't any, or perhaps I am
                Googling the wrong words.

                Thanks,

                Timm

                --- In William-Optics@yahoogroups.com, "Scott Walker" <sdwalker@c...>
                wrote:
                >
                > Someone has already answered the color question. I thought I would
                answer your question on what the graph means. The graph shows how
                different wavelengths focus as a function of lens radial position.
                The bottom of the y axis is the center of the lens. The top is the
                outer diameter. Restated this graph shows the spherical aberration of
                the lens at different colors and chromatic aberration. The eye is
                most sensitive to light around 550nmeter, so the graphs should be
                about a straight line at this wavelength in a well designed lens. The
                graph for the Fluorite Doublet shows the lens to be very well
                corrected at all but the wavelength extremes. At 435nmeters the focus
                point is about .125mm from the 550nmeter point. (typically the focus
                position is calculated at 70% of full aperture). This shift in focus
                will cause a blur diameter of about .02mm (.125/f-stop). So at 435nm
                the blur is much larger than due to diffraction(around .008mm). For
                visual use this is of little concern because the eye has very little
                sensitivity at this wavelength. One of the questions floating around
                has been what is the difference between an APO doublet and an APO
                triplet. WO address this question with the longitudinal aberration
                chart shown in Megrez 80 fluorite triplet. It shows the curves for a
                doublet and a triplet. In general the triplet can bring the focus
                points a the 70% of max radius, much closer together over the full
                visual range. Also look at the curves for the Megrez 80 II ED triplet
                APO. Even though it uses a lesser glass than the fluorite doublet,
                the color correction at the extremes is much better. The comparison
                between a triplet and a doublet is also shown on the WO website in
                the 66 ED APO section. Here spot diameters are shown. As one can see
                the spot diameters are much small at the wavelength extremes for the
                triplet. The photographic process tends to be more sensitive to the
                color extremes. This is why triplet are often preferred for
                photographic work. I hope this helps.
                >
                > Scott
                >
                >
                > ----- Original Message -----
                > From: Timm Bottoni
                > To: William-Optics@yahoogroups.com
                > Sent: Monday, January 23, 2006 7:19 AM
                > Subject: [William-Optics] Re: Colour coding on the aberration
                graph
                >
                >
                > Good question Dmitri!
                >
                > I want to know more than that, I also want someone to explain how
                to
                > read it and what it really means.
                >
                > I want to be able to add this to the FAQs I am working on for the
                > group, as well as for my own understanding.
                >
                > I actually went out and downloaded the Zemax demo, but even after
                > reading and understanding the basics, and searching Google, I
                still
                > don't understand what the charts mean, to be honest, and how to
                use
                > them to compare one scope to another.
                >
                > The real software costs $2000-$4000 and then you have to pay for
                > training, so maybe this is one of those things that you can't
                learn
                > for free, but lets see if anyone has an explanation in our group.
                >
                > Anyone? Tom? Ron? Anyone feel free to offer to explain these.
                >
                > Also - Tom Trusak has posted his opinions and thoughts on
                doublets
                > vs. triplets, and I will try to includes some of that in the FAQs
                > since it comes up often as well. I have a few sites that are
                very
                > technical, but if anyone has an easy web site that helps explain
                it
                > feel free to post it.
                >
                > The majjority of companies do NOT post these types of charts, or
                the
                > glass specs, or the color correction levels, or quality control
                > specifications. Perhaps WO is just more honest, or perhaps they
                feel
                > that the charts help people, or perhaps other companies just
                don't
                > want to open the kimono that far because it lets competitors see
                what
                > they are doing, and gives them a chance to try to one-up them
                with a
                > better looking chart.
                >
                > Either way - if anyone has any information, let us all know.
                >
                > Timm
                >
                > --- In William-Optics@yahoogroups.com, "kulginoff"
                > <dmitri.kulginov@e...> wrote:
                > >
                > > I would like to know the colour legend on the chromatic
                aberration
                > > graph for Zenith Star Fluorite Doublet on the WO web site,
                > >
                > > http://www.william-optics.com/wowebs/prod_tel/zsfd80/chrom.htm
                > >
                > > Thankfully,
                > > Dmitri
                > >
                >
                >
                >
                >
                >
                >
                >
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