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Old 08-12-2009, 11:36 AM
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avandonk
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Cosmic Rays and Your Sensor

I have taken thousands of darks over the years and and on Sunday night a cosmic ray was almost perfectly parallel with the sensor.

The first image is the 8 min dark at 1600 ISO jpg straight out of the camera.

The second is a grey scale of a fit from the area (100% crop) where the cosmic ray hit. I subtracted a dark frame.

The third is a bayer interpolation from the fit of the same area.

We can learn a few things from this.

A cosmic ray most of the time only affects one pixel. This is why you should take many darks and median or sigma reject stack to get a master dark.

Correcting for for darks should be done in fit form. You can see after interpolation the colour track is fatter than the gray scale fit. So is the residual noise. This happened while the camera was cooling down so I do not have an accurate dark.

I used to collect x-ray data on image plates 400 mm x 400 mm and over about ten years only saw one cosmic ray track parallel to the image plate.

Bert
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  #2  
Old 08-12-2009, 01:50 PM
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That is a long cosmic ray hit. My CCD will get a hit on almost every frame when I do 2 min exposures but rarely that long. This seems to be common with some sensors. I read somewhere that it has something to do with what elements are in the cover slip on the CCD.
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Old 18-12-2009, 08:58 AM
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Having taken 10's of thousands of images over the last decade with cooled Astro CCD cameras, cosmic ray hits impacting a lot more than 1 pixel are a regular occurrance though I have not seen one as long as yours.
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