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I just took a 12 minute exposure at f22 because i am trying to figure out out to take really long night shots and for some reason the corners are bright and there are spots all over the picture. Is this normal? It wouldn't let me upload it on this website so here is a link http://www.flickr.com/photos/36682328@N05/3433735201/
Did you choose F22 because it forces long exposure? Or because of the sharpness? Because F22 is going to cause diffraction deluxe.
*if* you chose F22 as your aperture, just to force longer exposure (I am assuming here, because I see no other technical benefit for this choice) you may want to go back to a lower aperture and use a neutral density filter to stay at apertures where your lens and camera perform best (say F8) and use the filter to force longer exposures.
Just a thought.
Also: close your viewfinder when doing long exposures. Light can sneak in and do weird things sometimes. (emphasis on sometimes).
Thanks for the quick reply...i was just trying different apertures and wasnt sure if that was normal or a fault. I have seen shots where stars streak or circle and was wondering how to do it but it was super bright at low aperture.
Did you cover your view finder during the exposure? What type and model of body did you use?
That is normal. The "spots" are hot pixels, the bright corners are amp noise, and the rest of the noise is thermal noise. It can help to do dark frame subraction ("long exposure noise reduction" in Canon settings). Astrophotographers buy or modify their cameras with themoelectric cooling units and more.
I haven't done many long exposers at night, but the ones I did, those "hot pixels" or whatever where immediately corrected when I imported them into lightroom.
The view finder wasnt covered and it was a sony a300 body. Thanks for all the replies I was just worried that something was wrong with the camera as I have done other long exposures for shorter times and not seen these effects.