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Re: [ATM] BSC1/F2
Bob May wrote:
> I missed one part of the spec. I've got 200mm dia. glass for the
> BSC1 and F2 glass which, of course, makes the design a bit more
> difficult to do. Unlike reflectors where the design can usually
> be scaled up or down without much care, refractors do tend to
> blow up badly when sized up as Richard knows.
You didn't say what kind of F2, so I'll use Schott instead of
Sumita. My version of OSLO has an value for Hoya BSC1 in its
"Obsolete" catalog, so I have some Cauchy coefficients to use
in the GSUM tool. I can set up for the "unnamed" catalog and
use "Schott" style coefficients -- in the order given in the
OSLO catalog, A0 = 2.2501594, A1 = -0.00878433, A2 = 0.011271737,
etc.
I don't know how thick the glass is, so I'll keep it thin-ish,
say 10% of the semi-diameter for the convex edge thickness and
12.5% of the semi-diameter for the concave central thickness.
In the end, I kept the central thickness of the convex lens
at 25 mm -- about 9.7% edge thickness ratio -- you may have to
think about this...
200 mm diameter glass... let's say 190 mm clear aperture -- that
makes the extra diameter 5% (10 mm /200 mm). Let's design the
best performance for the e-line, so you can, if possible, use
that line for testing. At first, I'll allow the two inner
radii to not match and adjust the air-space to get the 70%
longitudinal error down to zero too to provide a really good
null -- it ends up a bit under lambda/400 P-V.
We'll tweak the minimum focus wavelength to achieve standard F-C
correction -- the F and C lines crossing at the sqrt(0.5) zone
( ~70.7% ). Turns out that occurs when the GSUM minimum focus
wavelength is 559.234 nm.
The result is at:
http://users.rcn.com/rflrs/dbl02-54x.len OSLO input file
The visual Strehl ends up here at about 0.4682. By shifting the
color correction bluer, the two inner radii could be made equal,
allowing them to be tested against each other -- like Dick Parker
described in the video on the Stellafane web site. In this case,
however, that makes the correction too blue, and the visual Strehl
drops; maybe it's due to this being at f/8. Oh, well...
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