Yesterday as I was trying to create some studio-like photos in a home-made setting, I learned about a not so obvious link between shutter speed, aperture and the amount of shadows in a photograph. This definitively isn’t brain science – but it does seem a bit unusual. Suppose you have two sources of light, a natural side-light and an artificial flash. You can’t control the natural light, but the flash is a different situation – you can actually set its power (or let the camera set the appropriate power) and suddenly you’ll get some control over the light in the photograph.

Now comes the next factor, the shutter speed/aperture setting. Since these two are very much linked to each other, we can refer to them as just one factor (and not two). If the power of the flash is set to automatic, then the actual value will depend on the shutter/aperture setting – if it’s something like 1/60 with f1/35, then the power will be lower than for 1/125 with f1/8. But if the flash power will increase, so will the amount of shadows caused by the flash.

Therefore, if one wants to use the flash in order to eliminate shadows from another source (sometimes called fill-in flash, but I had to use the flash in the regular mode to get more control), the shutter/aperture factor can play an important role – a slow shutter speed with a wide aperture will let less light from the flash inside, but a fast shutter speed with a narrow aperture will let more flash light inside (at least compared with the other light source).

This is caused by the power of the flash, a similar effect can be obtained by fixing the flash power and setting the shutter speed/aperture according to that value – this approach does provide a more control, but in a more difficult manner.