Re: Photographic Size of a Star

"Chris L Peterson" <clp@xxxxxxxxxxxxxxxxxx> wrote in message
news:r2kom25p3s42jvpq1dplc1r64bvhggksqu@xxxxxxxxxx
[snip]
The stellar profile typically has an approximately Gaussian profile. The
apparent diameter is determined by the intersection of that profile with
the noise floor of the detector. As the star brightness increases from
the limit of visibility, you initially see a rapid increase in apparent
diameter. Then, over a range of increase you see a steady, but smaller
increase in the apparent diameter. Above a certain brightness, the
apparent diameter again increases rapidly with increasing brightness.
[snip]

Chris,

On a related topic: do you or anyone else know WHY we have an increase of
apparent diameter on photo and digital plates for brighter stars in the first
place?

What exactly causes the circular saturation, i.e. the increase in diameter in
photos? Is it stray light, scintilation, or is it a property of the detector
to saturate sideways, always?

I know that overexposure in normal photos tends to saturate sideways, covering
the boundries with excess light, but why does it happen on point sources?

Assuming of course the scope is properly focused as to produce pin-point
images!

Thanks,

Chris L Peterson
--
Ioannis
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The best way to predict reality, is to know exactly what you DON'T want.

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