[Aavso-photometry] CCDs vs. Single-channel Photometry

[Richard Miles]

Jeff Hopkins wrote:
> While determination of the sky condition could warrant determination of 
> standard deviations of comparison stars, for normal work, I do not think 
> that necessary.....
>Aside as noted above, doing standard deviations on the comparison stars is 
>rather meaningless as the whole point is determining the program star 
>magnitude.

===>  Jeff, I think you and Michael are talking at cross-purposes somewhat; 
Michael is specifically referring to how it's best done using CCDs whereas 
single-channel PMT-based photometry is as how you describe.  The two 
techniques are very different and have different strengths and weaknesses.

>
> I'm truly surprised there are not more people doing single channel 
> photometry, particularly photon counting. It is certainly much easier, 
> much cheaper and appears to be more accurate. I'd be happy to help anyone 
> interested in pursuing that.
>

===>  Your offer is noted, thanks.  I hope one or two people on this list do 
take up your offer.

===>  May I just add one thought to highlight an important consideration 
though.  What you write is quite true and is typical where you have very 
good skies in terms of constancy of transparency as is the case for most of 
Arizona for a good proportion of the months in the year.  However, as is the 
case in the U.K., where the sky conditions are often very poor, CCDs offer 
the great advantage of being able to cut through most of the sky 
variability, within limits, so that accurate differential mags can be 
secured even under relatively adverse conditions - using a single-channel 
detector would be hopeless in such conditions.

===>  So a word of warning to 'would-be' single-channel photometricists, if 
you are frequently treated to superb skies then by all means get a 
single-channel photometer and you will be able to do some great observing. 
However, if photometrically-clear skies only appear once or twice a month, 
then stick with your CCD.

Richard Miles

P.S.  One other strength of single-channel photometry - The data reduction 
process is vastly more straightforward and it's great to get your results 
virtually in real-time.  This is my biggest issue with CCDs at present.