I was shooting in low light recently and also wanted to do HDR so I had exposure bracketing on. With bracketing, you can take 3 individual shots or use sequential shooting.

I was surprised that my images were very noisy with a fair few hot pixels and salt and pepper noise all over. These exposures were typically 4 to 8 second exposures at ISO100 and 200 and the camera (E-P1) normally does a smashing job. After looking through the camera manual a bit, I discover that noise reduction is turned OFF when using sequential shooting. D'oh - that's what I did wrong!

I just did some test shots at 60s and let's just say the difference is phenomenal. I won't be doing that again. With noise reduction and single shot, no hot pixels and very little salt and pepper noise.

I don’t know about the E-520, but if it behaves the same, make sure you DO NOT have sequential shooting turned on for long exposures.