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[OM] Re: focus and ? about lens filters

Subject: [OM] Re: focus and ? about lens filters
From: Andrew Fildes <afildes@xxxxxxxxxxxxx>
Date: Wed, 9 Jan 2008 19:35:11 +1100
On 09/01/2008, at 12:54 PM, Chuck Norcutt wrote:

> I could hypothesize that the front element is actually a Schmidt
> corrector plate to correct the coma of such a fast optic.  The
> characteristic of a Schmidt corrector is that it looks nearly flat to
> the eye but isn't.  The front is flat but the back side has an  
> extremely
> shallow sinusoidal-like curve.  Commonly used in Celestron and Meade
> catadioptric telescopes for the correction of coma in fast, spherical
> mirrors.  I don't know of any cases where a Schmidt plate is used in
> conjunction with all-refracting optics but I don't see any reason  
> why it
> couldn't be.  That's my 2 cents.

If you're using words like catadioptric and sinusoidal, that's at  
least $10.02 worth!
Andrew Fildes
afildes@xxxxxxxxxxxxx
www.pbase.com/afildes


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