Re: ATM How to find the optical center

[Brian Nestel <blast@aloha.net>]

Steve Bell wrote:

> 
> I've thought about this myself. While the optical center is not
> guaranteed to lie at the geometrical center (ie, at the center of the
> circle), it does lie where the lowest part of the parabolic surface is
> located. So, just level the mirror with its face pointing up and drip a
> drop water on it. Where this settles is the lowest point, which if the
> parabolic surface is symmetric from that point on out to the rim (ie, no
> astigmatism), will be the optical center. I haven't tried this myself,
> but I will the next time I clean my 16".
Hi:
A drop of water may not make to the center due to friction and surface
tension
because of the small angular difference.
I've found the center by using a small plastic bead, you just make sure
the
mirror is level across the top edge, roll a bead on it, mark where it
comes
to stop using a dry marker, repeat this a few times and average the
difference
and it will be close to center, then just clean the marks off and put a
permanent marker. I would not recommend a steel bearing, but everyone's
wife or girlfriend has a broken necklace around and if you are a female
atm you probally have one yourself. 

-- 
Aloha   159 36 W, 21 58 45 N
Brian   Middle of the Pacific,
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