Picture Doctor: 4 Ways to Tame Flare

WHAT'S THAT BUTTON FOR?

Depth-of-field preview: How many times have you read (in this magazine, even) to check your depth of field? How many times have you said, um, how?

1. The button: Usually obscure, and often unmarked, a small button or lever somewhere on the body of your film or digital SLR. Not all cameras have them. Check your camera manual for existence and location.

2. What it does: It mechanically makes the diaphragm in the lens close down to the aperture (f-stop) you've set on the camera. It may work only in manual and aperture-priority mode, sometimes program auto.

3. Why? The lenses on SLRs keep the aperture open wide so that you can see the image nice and bright in the viewfinder. It closes down only at the moment of exposure, then pops back open again.

But to see the depth of field (how much in front of and behind your subject will be in good focus) you have to view through the diaphragm when it's closed (stopped) down to the aperture you (or the camera) have set. The button does that.

4. How? Press the button, and the viewfinder image will get dark. It's supposed to do that. And of course you can't see anything, at least very well. Here's the trick: You have to let your eye acclimate to the dark image. Keep your eye glommed to that viewfinder. Close the other eye. Cup your hands around the viewfinder (a tripod helps here). Outside, wear a peaked cap or a floppy hat and shade the viewfinder with it.

You should be able to make out the image now. Everything in focus that you want in focus? No? Use a bigger f-number (f/8, f/11, f/16). Too much in focus? Use a smaller f-number (f/4, f/2.8, f/2).

AND JUST WHERE IS IT?

Depth-of-field preview is the little diaphragm icon on Pentax/Samsung DSLR on/off switches. On other cameras it's even more obscure.