[Aavso-photometry] Cosmic Rays

[Ben Davies]

You say cosmic rays at "half a dozen electrons". That's a little tight. 
What is your noise level?

Hi Michael,

The noise level is essentially 0.  Try this for yourself.  I think you 
will like it.

-Make 3 dark frames of 30 minutes each.
-Median combine them
-increase the magnification to 400% and  blink one of the darks with the 
median.  It is absolutely amazing the 'vermin' you will see revealed in 
the image.  At least you will if you have the same sort of radiation 
hitting the chip that I do.
- Then subtract the median from one of the darks.  This leaves you with 
an image that has only the cosmic ray artifacts (no asteroids here) and 
near 0 background level.  The background is going to bounce around a bit 
from pixel to pixel (-1 to +1) because the median is of 3 images and you 
are only subtracting it from one of them.

The process with actual starfield images is as I described in a previous 
post.  As Wolfgang points out, there needs to be a better combining 
routine than averaging, but that will do until one comes along.

Ben Davies