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Mark IV Lens System
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- Subject: Mark IV Lens System
- From: Tom Droege <email@example.com>
- Date: Sat, 03 Jan 1998 16:16:57 -0600
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I have asked Elliot Burke to work on a lens system for the
Mark IVs. He hopped right on the project and has a preliminary
design. It will use a 4 element lens. By taking advantage of the
fact that we will always use a lens with a filter, he can design
at lower cost, and possibly better than a camera lens. It is
(at least) a quadratic problem, and so should get a lot easier
as the bandwidth is restricted.
By buying 50 or so at one time we will get a price (we hope) that
is favorable compared to camera lenses. I have also specified a
field of view that is right for our CCD. We know camera lenses are
not so good in the corners. I find a 400mm f/2.8 in Keh for $3959,
a 400mm f/4.5 is $1219. We hope to beat the lower price. Note
that this is high risk, and a lot of money for me. We want to get it
right. I know this is hard. Now is the time to speak up if you know
anything. It would be sad if say 600 or 300 would be a much better
Another advantage is that we will get identical units. This will allow
a standard focus motor design, and other such improvements. A
motly collection of camera lenses would be a pain.
The design that I have specified is a 400 mm f/4. Is this "right"?
I have also specified the following band passes:
Bessell B 390-470 nm
Bessell V 490-585 nm
Bessell R 570-690 nm
Bessell I 730-950 nm
Note that I just estimated these from the curves that came with the
filters from Omega Optical. I am sure that the cut off will not be so
sharp that a few nm one way or the other will make much difference.
If someone knows (or can look up) the exact pass bands let me know
and I will correct my spec to Elliot. I used half max at the edges.
We hope that such a lens will get the survey to mag 16 at a darker
location, or we can cover more area with shorter exposures. This
should be close to finding moving objects.