The Not So Perfect Automatic Exposure I actually wanted to post something about using flash today but realized the point had so much in common with a flash-free exposure that I decided to take it step by step. So bear with me please, I will get there.

Sometimes, even today's great cameras with their 'smart' evaluative metering just don't do what we want them to, whether in full automatic, aperture priority, or shutter priority. Most articles I see recommend using exposure compensation in these situations. While usable, it is often unpredictable and either results in you checking the exposure almost after every shot and adjusting and reshooting, or some shots end up under or overexposed.

What is going on here? Say you are photographing a skier. With the white snowy background, you throw in say +1.7 EV exposure compensation and start shooting. When you download the photos to the computer in the evening you notice that all of the wider angle shots with large areas of snow and a small figure of the skier are perfect while the ones where the skier got closer or you zoomed in have the skier overexposed. As you change your composition and either include more or less of expansive white area, the automatic exposure is either more or less accurate. And then you add a fixed +1.7 EV on top of that! So with the skier filling the frame, you would really need +0.3 EV or +0.7 EV, while more snow requires +1.7 EV or even +2.0 EV.

The same scenario can happen while photographing birds in flight. As you pan with them, your background can change from blue sky, to green trees, to bare trees, or something even more dramatically different. As the background brightness changes, the camera adjusts its exposure even though you may still be photographing the same bird in the same light.

In these situations, I find the manual mode so much more predictable to use. When you switch to manual, the meter is still active and you will see the reading in the viewfinder. Establish the right exposure for your subject and leave it. Now unless the light changes your skier, or your bird, will remain properly exposed no matter what happens to the background and you can keep shooting knowing your results are going to be more consistent! To be on the safe side, you can still check your exposure once in a while especially if you suspect the light changed enough, like the sun going behind a cloud or emerging.

The same applies to product photography. Many times, you may need to photograph the same object against a variety of backgrounds. With the automatic modes, you will be stuck constantly adjusting your exposure compensation. If you go with the manual mode, you measure your light once and then you just keep shooting!

In the example above, I set the camera to evaluative metering and aperture priority mode at f/8. While I was photographing the same vase and the right exposure should really remain the same, you can see it did not. With the black background, the camera tried to brighten it up and bring the scene average closer to 18% gray, choosing 4.5-second exposure (yes, it was pretty dark since I did not bother setting any lights up). Then all I did was swap the background for white. Now the camera tried to do the opposite and darken the overall image towards an 18% gray, resulting in a 1.5 second exposure.

Where was the right exposure? Somewhere in between. If I chose an 18% gray background my exposure would have been the closest. And for product photography that is just what I like to use to get my exposure right - an 18% gray card. It will serve you two purposes. You can set your manual exposure off of it and you can also set your custom white balance off of it. Go get one if you don't have one yet.

Have fun!