9 replies to this topic

[austin.grant]

Attached is an 800 x 800 pixel crop from one of my 30-minute Dark frames. I'm getting bizarre artifacts in each one, and they are completely random. It's been suggested that they are cosmic ray strikes, which would mean that each of my 30-minute Darks has around 100 strikes. I've nothing to base an opinion on, so I thought I'd ask you guys. Is that what these look like? Oh, and the shot had a minor stretch applied to show the artifacts better, and then I highlighted some of them. The number of them is fairly consistent between dark frames, and the placement and appearance is totally random. Also, if that is what they are, how do I calibrate them out? Just shoot TONS of Darks?

[Konihlav]

Austin, it is normal that some sensors are more sensitive on these "hits" then others. It is normal that you have to take couple of (10-15-20 pieces) of dark frames and create a master dark by e.g. median stack method which eliminates them... for darks it is important to make a set of them for each different set-point temperature (and binning of course...). The resulting stacked master dark will then be OK to use for calibration purposes...

[austin.grant]

Thanks for the reply. I hadn't considered that some sensors might be more susceptible than others. I guess that's why I've never noticed them with any of my other cameras.

[CharlesW]

You may find this interesting concerning "cosmic worms" and other hits. http://www.astronomy...cRays_groom.pdf

[austin.grant]

Thanks for the link, I'll check it out. 

 

When I teach radioactivity in my Chemistry classes, we actually build a cloud chamber and view the decay of Pb-210. Though I've seen where people build cloud chambers for the sole purpose of observing cosmic rays, I've never had the conditions just right for my classroom setup to see them. I think I'll bring in this CCD next semester and we can capture some and check them out onscreen.

[blueman]

Attached is an 800 x 800 pixel crop from one of my 30-minute Dark frames. I'm getting bizarre artifacts in each one, and they are completely random. It's been suggested that they are cosmic ray strikes, which would mean that each of my 30-minute Darks has around 100 strikes. I've nothing to base an opinion on, so I thought I'd ask you guys. Is that what these look like? Oh, and the shot had a minor stretch applied to show the artifacts better, and then I highlighted some of them. The number of them is fairly consistent between dark frames, and the placement and appearance is totally random. Also, if that is what they are, how do I calibrate them out? Just shoot TONS of Darks?

Cosmic-Rays.jpg

Because they are random, they will be removed when you make your master. I see them all the time in lights and some time in darks too.

Blueman

[gavinm]

That is EXACTLY why you take tons of darks. Hours and hours and hours of them.

[austin.grant]

Cool, thanks everyone! I was mainly just surprised to see so many events, but I guess 30-minute exposures are pretty long.

[blueman]

Could be that you just chose a time to take them where the hits were high. I don't take more than 10 darks myself, just haven't seen any difference when tried 50 then 30 then 20 then 10. SO I just settled on ten.
Flats I take 15, again same situation, diminishing returns for more.
Blueman

[andysea]

I notice more cosmic rays in my images taken with the KAF3200 than in the ones with the KAF8300. I always thought it was pretty cool to see their traces and they calibrate out very easily.