mdgrwl wrote in post #11614831
I just cleaned my sensor the night before and I didn't want my shutter open for 20 seconds to shoot at ISO 100. Also, the longer my shutter was open (around the 6 second mark), the photo's were starting to get over exposed even in Av mode stated it was correctly exposed. So there were a few reasons why I choose to shoot at the higher ISO. Plus, the 60D handels high ISO so well, it didn't impact the photo.
A 20 second exposure isn't going to cover your sensor in gunk, if it did then those that used live view for minutes at a time would have balls of fluff in their mirror boxes by now. As for why you were getting messed up exposures I don't know, but even so you could just do some simple math. 2000/100 = 20, 4 seconds x 20 = 80 seconds. So, if the camera was really giving you 20 seconds that'd actually be 2 stops under exposed. Not sure if the camera can even expose for more than 30 seconds outside of bulb, but you still could've done something like ISO 500 to get 16 seconds.
As for it not impacting the photos, I'm not sure how well your monitor is set up but I can clearly see a fair bit of noise in the blacks, and even where you've either tried to clean it up or you've adjusted some settings like saturation or contrast and it's made it stand out even more.