Re: [ATM] 8" Diagonal- More info

[Mark Holm <mdholm@telerama.com>]

I get 0.39 arc seconds for the first minimum diameter, so, if I did that
calculation right, the scope's resolution is still pixel size limited,
although the match between pixel size and Airy disc is not outrageously
far off.

With smooth 1/4 wave (wave front) zonal errors, most of the light that
is split out of the Airy disc goes into the first "gap" and the first
ring.  Those are still inside the pixel size.  Higher frequency errors
would throw the light a little farther out.

Mark Holm

Dream - Telescopes & Accessories, Inc. wrote:
> Mark,
> 
> It appears Scott will be at 0.7 arc seconds/pixel with his 28" f3.7 and
> STL-11000 combination.  Correct me if I'm wrong Scott.
> 
> Thank you.
> 
> Sincerely,
> Shane Santi - Owner
> Dream - Telescopes & Accessories, Inc.
> http://www.dreamscopes.com
> 610 - 365 - 2833
> 
> 
> 
> At 02:27 PM 12/26/2005, you wrote:
> 
>> Polaraligned wrote:
>>
>> > Holding 1/10 wave or better is the priority and I know that the
>> > edges are going to fade from this value.
>>
>> Pardon me for being blunt, but why the emphasis on surface accuracy for
>> an instrument to be used at prime focus with a ccd camera?  Your
>> resolution is going to be nowhere near diffraction limited, instead, it
>> will be pixel size limited.  I'll bet, a calculation would show you can
>> tolerate wavefront errors that would horrify a planetary or double star
>> observer and still produce ccd images not even measureably below
>> "perfect" quality.
>>
>> Maybe save some money by putting looser specs on that huge diagonal and
>> put the money into a quick change arrangement on the secondary mount, so
>> you can switch to a smaller, higher quality diagonal for visual use.
>>
>> Mark Holm
>> mdholm@teerama.com
> 
> 
> 
> 


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