You can't stop down by a hole in the center, as that is where the
central secondary mirror is and there is no light there. The mirror
diameter as a percent of the main mirror diameter is what will
determing the contrast possible with this type of lens, whether it is
a camera lens or a telescope. These small camera types have probably
at least 400bstruction. The general rule for astronomy scopes of
this type is no more than 200bstruction for the best contrast. You
should be able to cut an off axis hole to reduce the amount of light,
but the reduction will be large since there is not much diameter to
work with in the annular space around the central secondary mirror.
This technique works well with much larger astronomical scopes to
reduce the light when viewing bright objects like the moon or the sun
(proper solar filter still required).
--- Jeff Keller <jrk_om@xxxxxxxxxxx> wrote:
> I forgot to post the link
>
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2946763446&category=3
> 344&rd=1
>
> Its a mirror lens. I've yet to see a snappy aperture on a mirror
> lens.
>
> FWIW I asked an yaBe buyer who picked up a right angle camera mount
> why
> he got it. The buyer had lots of feedback. I was surprised he
> didn't use
> a Varimagni finder. Turns out he spotted that it had an aperture in
> it
> (that can be stopped down) and he wanted to use it with his mirror
> lens(es). The seller claimed it was made by Olympus which I doubt
> but it
> was probably made to work with Olympus microscopes. It sounds like
> something to try. I suspect a large lens cap with a large hole cut
> in it
> could give a one stop aperture to make up for focusing errors. More
> things to try...
>
> -jeff
=====
Don Shedrick
http://groups.msn.com/firstlightimaging
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