I've been trying to do some long exposures, mostly to get some halfway decent pictures of the stars at night. I've been in places with little ambient light, and the stars aren't really visible. On top of that, with long exposures the top corners of the photos get REALLY bright and I'm not sure why.
So, my questions are these: how do I fix the bright corners, and what are some good settings for star field photos? The picture below (supposed to be stars and also has the bright corners) was taken w/ 25sec shutter, f/25 aperture (iPhoto lists Aperture and Max Aperture, and the max was f/4.0, so I'm not sure which one is which), 22mm focal length, no long-exposure NR, D-Rage optimizer was just set to D-R, and ISO was 1600. I was also using a UV filter.
One last question...Neither of my lenses have focus marks on them, so I'm not sure how to set focus for infinity for good star focus (and autofocus won't work because it's so dark haha).