This post is not fun, nor is it entertaining: it is about obtaining useable exposures.
When we contrive to admit “the right amount of light” through a shutter, do we believe what our meter recommends (and perhaps interpret that for our purposes)? Or do we get it “wrong?” If the latter, then which is preferable: overexposure or underexposure?
I lean toward overexposure as the lesser of the two evils. The raking angle of sunlight (however dramatic), the short winter days, and the ongoing problem of “artificial” light sources all contribute to empty shadows that we expect to reward with information but do not.
Light sources within the frame and large portions of sky in the picture both conspire to underexpose the rest of the landscape, or the room, or whatever. Point the lens down at the ground to take a meter reading, then use that exposure when you compose the frame.
Some photographers find it useful to “bracket,” to shoot a recommended exposure, then to overexpose and underexpose for insurance. This is a last resort, and one may never get a sense of how to deal with situations that re-occur. A reasonable version of bracketing might be simply to shoot what’s recommended and just one over, for the sake of the shadows (since modern films don’t seem to block up in the highlights as badly as they once did).
Your camera may have some sort of a +/- setting. You can move the indicator to +1/2 or +1 to add a half-stop or a whole stop. Alternately, you can reset the ISO, whether it is set automatically or manually. This can be done either for an entire roll or for just the frames you think need it.
After the exposures have been made, a last resort is to overdevelop the film; usually this means that all the frames on the roll will pick up contrast, for better or worse.
Creative Camerawork 