I use a Canon 7d and since getting it I have been somewhat disappointed with the amount of noise I get in my shots compared to my Rebel. Tutorials suggest shooting overexposed to reduce noise however when I try that I seem to just get the same amount of noise when the exposure is lowered in post for an acceptable composition. Therefore, my question is, what causes noise, Low light levels on the subject or low exposure level? Will more light on the subject reduce noise (obviously, in studio)? Your thoughts are appreciated. Thank you.