Long Exposure Theory

When out doing night photography like the shot above, you don’t want to waste time guessing what the exposure time should be (like I did here one bank holiday morning…)

The technique I use is to do a shot at a very high ISO speed and a smallish exposure time, then use that to adjust for composition and check the histogram. Changing the ISO from 1600 to 800 (for example, doubles the exposure time. So to get back down to ISO 100 requires a few doublings to get the right number.