Auto exposure modes can be great. Cameras have fairly accurate light meters that are getting better all the time. If you are walking down the street and see something pretty, you can pop off the shot without thinking and get a relatively good middle exposure.
Why Shoot Manual?
However, there are times where auto modes are actually worse for you than doing it manually. Let's walk through the raw photos from a shoot I did where I shot the whole thing in automatic exposure modes.
Here we have a decent exposure, if perhaps a bit dark.
This one was taken a few seconds later, and all I did was turn the camera. I'm not sure where my center point was for the camera to meter, but it must have been on his jacket, because there's no way this is properly exposed.
Were I in manual mode, this is exactly the exposure I would have taken. Well done, camera.
What happened? You were so close a second ago! All I did was swivel over a few feet and it got completely messed up. It was a very cloudy day so there wasn't even any sun, otherwise I could understand.
I live in Seattle where it's cloudy all the time, so no matter where you are outside, it's pretty much the same exposure reading anywhere you go. (Notice the complete lack of shadows under their feet.) If you're in a situation with rapidly changing light, where you are moving from bright sun to deep shadows, then auto exposure modes have their place. But if you're shooting indoors or on an overcast day where the light isn't changing, all it takes is a few seconds to set your exposure, and then you get perfect exposures for every photo. In auto mode, the camera is constantly working, even when there is no work to be done, and you'll get similar results to mine. This one's too dark, this one's too bright, so where's the perfect one in the middle?
How to Practice Manual Exposure
There are only three things that affect your exposure: aperture, ISO, and shutter speed. (There are four if you count White Balance, which you can learn more about in my article about Kelvin.) Focusing on those three areas, here's how I approach setting a manual exposure.
- Set your aperture. The aperture is the only of the three controls that affects depth of field, so decide what depth of field you want in your photo, and set that as the aperture. Often, I will set my camera to either wide open or one or two clicks shy of wide open, just to let in the most light possible.
- Set your shutter speed. If you are shooting handheld, as I always am, be sure that your shutter speed is no slower than 1 / focal length. (Shooting at 100mm? Shutter speed must be 1/100sec or faster for a sharp shot.) Again, I will usually set this one automatically to 1 / focal length, or slightly faster, for a sharp shot and to let in the most light possible.
- Set your ISO. Now this is the part that takes practice. The other two are usually easy since there are formulas to them. For ISO, you are "completing" your exposure. Look at your scene, and then look into your viewfinder and look at the exposure meter. If it doesn't say +0 EV, determine whether it is looking at a dark spot or a light spot for its metering, and adjust the ISO accordingly. With a little practice, you'll become incredibly adept at getting a proper exposure very quickly. And the best part is you only need to do it once, and then every photo of that subject will be exactly the same. No wild fluctuations in exposure.
Shooting in different light situations, but those light situations aren't changing? A lot of cameras give you the ability to save custom preset settings.
For instance, at a wedding, I'll set C1 on my Canon 5D3 to meter for indoors. I'll set C2 to meter for window light. I'll set C3 to meter for outside. Then I'll change my manual setting for anything creative that doesn't fit those other settings or when I use flash. And since I live in the land without sun (only sort of kidding), I can set those manual exposures during the getting ready photos and never need to change them until after dinner. All I have to do is click between my "indoor", "window", and "outdoor" settings.
So not only are my photos perfectly consistent, but I still don't have to think about camera settings. And isn't that the point of shooting automatic?