I have new kittens!
I’m not normally one of those people who takes hundreds and hundreds of pet photos, but I’m not completely immune either. This evening I turned around and saw them sitting on top of the cat tree looking utterly adorable. I also happened to have my 5D Mark II sitting on my desk, with a 580EX flash and a Sto-Fen Omni-Bounce diffuser attached.
If you’ve ever been around kittens, you know that they’re not terribly prone to sitting still for very long. I slapped the camera into P mode, turned the flash on, and started shooting. After a few shots, I looked at one of the images:
Yuck! Underexposed. I’d put the camera into P mode because I was in too much of a hurry to think about the proper settings for flash (which I almost never use), but I’d forgotten that the diffuser I was using steals light. You know how frosted glass doesn’t let as much light through as clear glass? The same thing happens with the translucent plastic of the flash diffuser. It does a great job of softening the harsh light of a flash, but it also means that your images will be underexposed if you don’t do something about it.
The kittens were staying put, so I had time to shoot a few more, but I wanted to get a better exposure. I knew from experience that the diffuser reduces light by about one stop, so I used the exposure compensation setting on the camera to overexpose the image by one stop. Actually, I screwed up and set it for one and a third stop of overexposure rather than one stop, but I didn’t notice that until later. The results, while not perfect, were appreciably better:
If you look at the full-size version of the image, you can see that there’s actual definition in the black fur. The white fur is a little bit blown out, but the net result is better than the first one. I could fix both of these to some extent in Photoshop, but it’s better to get it right in the camera. I haven’t adjusted the exposure of either of these, though I did crop them and sharpen the second one a bit.
So what is this exposure compensation thing?
Well, we already know that in most modes, including program, aperture priority, and shutter priority, the camera uses its meter to evaluate the image and then picks an exposure based on it. In manual mode, you do this yourself, though you usually use the meter as a guide. The camera does this by looking at the average brightness of the image and then picking an exposure that will best capture it. When using automatic flash, the camera also tells the flash unit how bright it should be. This often works very well, but in my case I knew something that the camera didn’t– there was a diffuser on the flash.
Exposure compensation tells the camera that it should overexpose or underexpose an image by a certain amount. In my case, what I said to the camera was, “Hey, camera. Make your best guess about the exposure, and then add one stop to it.” I did this by changing the exposure compensation setting to +1 rather than 0. Doing that allowed the camera to correct for the diffuser, and get a better-exposed image.
The exposure compensation on your camera looks something like this:
What you’re seeing is a representation of the camera’s meter, and an indicator underneath it showing what the compensation should be. When the arrow is under the zero, the camera will pick the exposure it thinks is right. However, when it looks like this:
the camera will add one stop to the exposure it thinks is right, resulting in a brighter image. If the arrow was under the 1 on the left, the camera would subtract one stop and the result would be a darker image.
Exposure compensation is useful if you know that the camera is going to predictably underexpose or overexpose an image. This might happen if you’re shooting with a very light background like snow, or a very dark background like a dark theater. There are lots of other cases where it can happen as well.
Oh! One other thing. Sometimes people discover that their camera is suddenly making all of their pictures too dark or too bright. They wonder what’s wrong, and think their camera is broken. What has usually happened is that they’ve accidentally set the exposure compensation, and the camera is doing exactly what it was told to. Also, don’t forget to set it back to zero when you’re done, or your next shoot will have lots of over- or underexposed image.
I hope this helps explain the basics of exposure compensation.
And yes, yes. I really did admit to using P mode on my dSLR. As I said above, I didn’t want to think about the right settings for the flash. I was in a hurry, because I wanted to catch the kittens before they moved. Plus, I wasn’t really aiming for super high-quality images– in essence, I used four thousand dollars worth of equipment as to grab a quick snapshot. P is only bad when it’s used for everything, or used without forethought or understanding of its weaknesses.