[Aavso-photometry] In defense of the ST-9 & CCD choice Considerations

[mlfleenor at charter.net]

Re: 2 arc-second/pix sky coverage  check out CCD Univeristy @ apogee's website.
http://www.ccd.com/ccd113.html

In re-reading Tim’s post I see that he  said 2-3  pixel sky coverage not 2. I was wanting to illustrate that as long as you are not running under-sampled that this criterion was not something that has to be explicitly followed. 

I use my SCT with a compressor and often run binned 2x2 yielding 1.24 arc-sec/pix resolution or ~ 2.4 pixel sky coverage- however many times I am running 1x1 @ 0.62 arc-sec/pix  resulting in 5-6 pixel sky coverage with my typical seeing. Clearly outside of the 2-3 pixel criterion yet my results are excellent. ( I often achieve 1mmag precision with R-band 5 minute averages with extra-solar planet candidates during out of transit baselines. ) 

My frustration with the ST-9 was due in part to some of the images having blocky stars- I was under-sampling! I also was running @ 2260mm focal length. I could’ve run the SCT @ f/10 but here again the fov would be much too small for me. 
 
 I do take a slight sensitivity hit but also need the resolution to resolve close stars. 
While the ST-9 may better meet the  magic sampling requirement there are other considerations.

 I bet there are a lot more folks doing photometry with SCT’s using ST8’s instead of ST-9’s .

Mike







> Mike, have you seriously found a recent posting or reference that
> gives a guideline of 2arcsec/pix?
> Arne