Warning: Don’t confuse your focus point in the viewfinder with the exposure metering pattern: for example on Canon DSLRs the focus points are illuminated red…so if you are only using the centre focus point remember that it’s the FOCUS point. Metering is a separate function of your camera. This is really important and takes a little getting used to so don’t worry if you don’t ‘get it’ straight away…but once you do it’ll become second nature and your photographic exposures will improve 100%, guaranteed!
Before we take a look at exposure metering, it’s worth remembering an important fact: your camera does not see the world as you do when you look through the view-finder. What it sees is a world of approximately 255 shades of grey ranging from pure black to pure white. This has an important bearing on how we approach ‘exposure’. But more of that later. For the moment let’s keep things simple.
Exposure is fundamentally about one thing: choosing the correct Metering patterns and fine-tuning (seasoning to taste) so that the final image is neither overly bright (over exposed) nor overly dark (under exposed). I’m aware that this is an over-simplification but I do want to keep things simple for now. The point being… it’s about what we do with the light we are given.
Light can be measured in several ways but in terms of photography we are primarily interested in just two: Incident Light and Reflected Light.
Incident light is that which ‘hits’ the subject: artificial or natural eg. Flash or sunlight. (As photographers out in the field it’s natural light that we are most interested in).
Reflected light is that which is reflected off the subject back to our camera. In other words, our camera ‘reads’ the reflected light that is bounced back towards us. And this is where we have choices about how much and in what way we want our camera to ‘read’ or rather meter that light.
All DSLR’s have several different types of available metering patterns. I show the Canon version below. If you’re not a Canon user then check your camera handbook.
Note that evaluative metering over-exposes a little automatically because the algorithm within your camera has been set to do this. Nothing wrong with this, and it works well but we need to bear it in mind for future reference.
So rule number one is: Metering Determines Exposure.
Everything else we do with the settings on our camera is ‘seasoning to taste’. To continue the analogy; if you give the same food to a dozen people they’ll all season it differently according to their own taste…but the actual food is the same for everyone. If the recipe is correct to start with then the rest is just ‘salt and pepper’. It’s exactly the same with our photography: if the exposure is correct to start with then everything else we do is just personal preference.
Now provided we haven’t chosen Evaluative metering (*see note below) and decided what part of our subject we are measuring the light from (it might be a bird’s white feathers or snow in winter) then we can select our priority program: Aperture priority or Shutter priority. These priority programs provide the seasoning to our exposure that we have already determined.
So rule number two is: Priority modes adjust the Variables
If you’re happy with the metering pattern you’ve chosen and the subject doesn’t change and the light doesn’t change and if you’ve ‘seasoned to taste’ then change nothing. Same light…Same exposure. If your subject moves to a different background in the same light then change nothing..Same light…Same exposure. (**see below for important note on Manual mode).
*Note on Evaluative Metering: The camera will constantly adjust settings to take into account any variation in background etc. Which means that we have to continually adjust priority settings to maintain the exposure we originally set.
**To maintain and fix your desired exposure then it makes sense to shoot in Manual mode otherwise you’re constantly playing photo roulette*, desperately trying to keep exposure the same. I’m aware that many of us shy away from Manual mode because it all seems a bit complicated with too much to think about, but believe me when I say that once you get the hang of it you’ll most probably rarely go back to Aperture priority etc. I’ll explain more about this in an upcoming post. Once you get your head round it life will be a whole lot easier and a whole world of possibilities will open up.
Meter the Light 