Friday, August 07, 2009

Why do lightmeters fail?

To understand why light meters fail, we need to understand what light meters do: No matter if it is a through-the-lens (TTL) meter as found on compacts and (D)SLRs or a handheld meter, they all try to reduce the scene to a neutral tone. This tone is often called "18% gray" but the ANSI standard against which the light meters are calibrated is a luminance value that is closer to the reflectance of 12% gray. 12% gray or 18% gray, we don't really care at this point, but what I would like you to bring back from this is that light meters generate those settings that will render the dominant part of your photo into a neutral colour. It may come as a surprise, but this will do nicely for most photos. It is not until you take a photo of a scene where this doesn't apply that you start to run into problems.

Ever tried to take a portrait on a sunny day where the face came out too dark? If your camera allows it, you could walk up to the subject, take a light reading and lock it, walk back to get the composition you want and the face will be well exposed. By this time it is also be a good idea to see if your camera supports spotmetering.