[Aavso-photometry] In defense of the ST-9 & CCDchoiceConsiderations

[Greg Crawford]

A couple of comments in the hope that I will learn from replies:

1) I am not sure why this thread is picking on the ST9. It is just one of a
number of CCDs with larger pixel sizes. Ultimately, pixel scale will depend on
other factors such as focal length, so that the larger pixels of the ST9 and
other larger pixel cameras may well give an appropriate pixel scale with some
systems. Furthermore, fewer pixels leads to faster download for fast-changing
targets. At the end of the day, every decision is a compromise, including
economic factors. Some factors beyond control, such as the exchange rate between
US and other countries, may make an ST9 the only economic choice and other
factors, such as local seeing, may make it the only practical choice; in both
cases achieving satisfactory results.

2) I have always been puzzled as to why FWHM is chosen as the point at which
sampling is measured. After all, the star profile usually continues to broaden
below half maximum, even though this may not be apparent from the contrast
regime of an image. If a star profile only covers 2 pixels at half maximum, may
it not cover 2.3 or even 3 pixels at one quarter maximum, so that a larger
measuring aperture will include sufficient sampling? 

Greg C.