Photography tips: The meter wants to see gray
Submit to HN In this post I’m going to try to explain in simple terms how a camera meters, and why you should take control of metering to achieve good shots.
Your meter is calibrated to produce the correct exposure for average scenes.
As it turns out, a good rule of thumb for average scenes is a particular shade of gray known as middle gray. Cameras don’t know what you’re looking at so they have to try to get the exposure right in most cases, so they just assume your scene averages out to this particular shade, which is pretty closely approximated by the color of grey asphalt. If you shoot a scene where the light averages out to precisely this middle gray you will get a perfect exposure.
In reality, few scenes are truly average.
Put too much sky in, and your average has gone way up. If you’re in a dark environment, your average is way low. But the camera has no idea about these things. It still thinks you’re shooting a middle gray scene, so it’ll underexpose the sky (treating a bright sky as if it was gray), or overexpose the dark scene (treating the shadows as if they were gray). If you shoot a nice snowy mountain, your meter doesn’t know the snow should be white, so it comes out gray. Thus: the meter sees gray. So, how do we get it to stop?
Take control of exposure.
There are lots of fancy systems for starting to think about exposure, but for me the best way to start getting the hang of it was to start using my eyes as a meter. This is a lot easier than it sounds because of something called the sunny 16 rule. Very simply, this rule says that on a bright sunny day, the proper exposure at f/16 is 1/ISO. So, if you have ISO 400 film in the camera, set your camera to 1/400 at f/16 and you will be very close to perfect for a sunny day.
Start shooting and see what the built in meter says as opposed to your sunny-16 rule. Try to understand why you or the camera were wrong for a particular scene. Usually, the camera may be wrong scenes that do not have a good mix of elements (all bright, or all dark), while you may be wrong if the lighting conditions are tricky (your scene has a variety of light and shade). You can’t really average a scene the way a computer can, but at least you can tell whether it’s sunny, while the computer does a pretty poor job at it.
But what if it’s not sunny?
No problem. All you have to do is progressively compensate for changing light conditions. As soon as it gets slightly overcast, you open up your aperture to f/11. Cloudy? f/8, is it getting stormy outside? f/5.6 and f/4. Dusk? f/2 and below. Similarly, you can keep the aperture at f/16 and simply keep halving your shutter speed as the conditions change. The key is experiment and the more you do this, the easier it will be to guess the exposure without even looking at your camera. I sometimes walk down the street and as the light changes, I change the camera settings and then meter the asphalt to see how close I am. Most cameras have a meter in manual mode and they’ll tell you how much over or under you are. Just make sure to point at the asphalt and not something too bright or dark.
So, armed with the sunny-16 rule you should be able to start getting a feel for the proper exposures, and start realizing when your camera has absolutely no clue. For all their fancy face detection and multi-point metering, cameras are still pretty dumb devices that are only as effective as their operators. Put a little thought into your next shot and see if it comes out a winner :-)
If you really want to understand metering:
- sunny-16 on wikipedia
- ultimate exposure computer – the holy bible of metering with your eyes
- the Zone system – developed by Ansel Adams
