[Aavso-photometry] Adequate FOV size?

[Arne Henden]

Tandy, David wrote:
> I assume the problem that arises with imaging brighter stars is that one
> should try to have comp stars brighter and fainter than the target star and
> that is not always possible at the brighter magnitudes, right?
> 
For CCD photometry, you just need comp stars in the general magnitude
range of the variable.  You do not need to bracket it, since CCDs are
considered linear in response.  So for the bright variables, you can
often (but not always!) find comps somewhat fainter than the variable
but still in the field.  The harder problem in those cases is matching
the color of the variable and the comps.

> Also, why is binning detrimental if a sampling rate (maybe 3 pixels per
> FWHM) is maintained?  I ask because I would still like to be able to shoot
> through a short focus refractor occasionally for some pretty picture work
> and small pixels are a better match at 800mm focal lengths while at 3556mm a
> 15-20 micron pixel works well.  Binning would provide that versatility but
> at what expense in accuracy for photometry?
> 
If you can retain 3 superpixels/fwhm in binned mode with the larger 'scope,
you will be ok.  What you lose is field since you are way oversampled
at the native resolution.  You just have to remember that the binning
takes place after the image is acquired, so "full well" and "dynamic range"
have to be understood in those terms.
Arne