Re: [ATM] Banishing the diagonal

[Ken Lowther <hermit@outofoptions.org>]

Well, if we are worried about the quality of images, we can just stay home and
browse the web for Hubble pix.....  I am not saying ccd's don't have their
place.  We are just getting into a different realm here.  Is the original
poster still reading this thread?  What was your goal?

Ken

Quoting David Whysong <dwhysong@gmail.com>:

>> So, in order to reduce diffraction you put the ccd in the light path 
>> and then
>> run cooling tubes to it?   Sounds like we have come back around to the
>> original problem. ;-)
>
> Secondary diffraction is rarely an issue for CCD imaging because the
> exposures are long enough that seeing dominates the PSF. (Spikes
> from a spider do show up, of course.) As for thermal issues, you simply
> insulate the camera.
>
> If I had the money, I'd build a 20" f/4-ish Newtonian with a large CCD
> and paracorr at the focus. The only reason to have a diagonal is that
> the SBIG research series cameras have a large and asymmetric shape,
> which might cause a "lumpy" PSF in good seeing conditions. That could
> affect astrometric measurements.
>
> --
> David
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Hermit, holed up in Youngstown, Ohio
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