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.
--- In William-Optics@yahoogroups.com
, "Scott Walker" <sdwalker@c...>
> 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.
> ----- 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
> Good question Dmitri!
> I want to know more than that, I also want someone to explain how
> 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
> don't understand what the charts mean, to be honest, and how to
> 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
> 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
> 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
> technical, but if anyone has an easy web site that helps explain
> feel free to post it.
> The majjority of companies do NOT post these types of charts, or
> glass specs, or the color correction levels, or quality control
> specifications. Perhaps WO is just more honest, or perhaps they
> that the charts help people, or perhaps other companies just
> want to open the kimono that far because it lets competitors see
> they are doing, and gives them a chance to try to one-up them
> better looking chart.
> Either way - if anyone has any information, let us all know.
> --- In William-Optics@yahoogroups.com, "kulginoff"
> <dmitri.kulginov@e...> wrote:
> > I would like to know the colour legend on the chromatic
> > 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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