Re: [ATM] 32" Focal ratio

[Aplanatic@aol.com]

Hmmm....
 
Aperture is very important, IMHO.  Suppose, for example, you are  hunting 
supernovae where limiting magnitude is almost everything.  The  limiting 
magnitude of an image increases as
 
5 * Log10(Aperture) + 1.25 * log10(Exposure) - 2.5 * log10(FWHM)
 
where FWHM is the full width at half the maximum intensity, a measure of  the 
seeing disk diameter.  Sky background is assumed to dominate the  noise.  If 
readout noise dominates the total noise then the picture is  quite different.
 
In other words, going from a 12" to a 32" aperture increases the limiting  
magnitude by 2.1 stellar magnitudes.  It takes an increase of a factor of  50 in 
exposure time to achieve the same increase in limiting magnitude, when sky  
noise dominates.
 
-- Dave
 
In a message dated 8/1/2005 7:02:07 P.M. Pacific Daylight Time,  
mbartels@bbastrodesigns.com writes:

> I  am going to be ordering a 32" mirror for a dedicated imager.  The
>  or will a corrector make this a non-issue?  What would YOU do

I  sure wouldn't mess with such large aperture.  Aperture is largely  
irrelevant in digital imaging compared to the camera, and mount.   Save the 
money for a better camera and go with a 12 inch.

Mel  Bartels 

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