When shooting from a tripod and/or with Live View on your (d)SLR you may find strangely exposed photos. Some are darker than others.
This could be related to the light seeping in through the ocular on your camera. Normally you have your eye against the ocular, but when you use e.g. Live View on your camera, you watch the LCD. This leaves the ocular 'open', and unwanted light might enter the camera and screw up the exposure of the photos you're taking.
I created a small example were I shot several high-speed images (in Aperture priority mode) while I used a small flashlight to pass a beam of light over the back of the body (e.g. car lights passing by in low light circumstances). I made sure that I also 'touched' the ocular with the beam of light.
You can see that the exposure goes from normal to dark, and back to 'normal'.
I haven't found any real differences when you're shooting under normal circumstances, but when (a strong) light is shining in or on the ocular, you might be in trouble.