Here’s the predicament. You’re taking a picture of your family in a dimly lit room, and you want everyone in the shot to appear completely in focus. If you use the highest f-number aperture available, you know you’ll be able to get the shot just right, but there’s a problem with that. It might make your photo turn out dark. Is there a way to solve this problem? Let’s have a look at Canon’s solution.
[Family photo by: Ariane Hunter]
It’s called A-DEP mode. The term is shorthand for Automatic Depth of Field, or just Automatic depth. With A-DEP mode, you tell the camera which parts of your photo need to be in-focus, and the camera picks a corresponding aperture guaranteed to get everything just right.
Before we get into a little more, let’s back up for a second. How does all of this work? On a very basic level, it comes down to the aperture. That’s what determines how much of your image is in focus. The aperture is the hole that light travels through to form an image on your camera’s sensor. The aperture setting is determined by the aperture value on your camera, usually denoted by an F followed by a number like F5.6 or F16.
When your aperture is fully open (a low F number), or as wide as it can get, you get the benefit of more light. This allows you to take better pictures in dimly lit spaces.
Unfortunately, this benefit comes at a cost. You get less depth of field, which is the amount of the scene that’s in-focus. More of the background and foreground get blurred, so you have be very selective about what you’re focusing on.
As you close off the aperture (higher F number), more of the scene comes into focus, but there’s a cost for that too. Less light passes through the aperture, and your images end up darker unless you also decrease the shutter speed to let in more light. And decreasing the shutter speed can lead to blurry images.
What Canon is doing with A-DEP
By now, you should start to see a pattern emerging. There’s this constant tradeoff you have to make between the depth of field and the amount of light you allow into your camera. Wouldn’t it be nice if you could only let in as much light as you need to just get the important parts of your image in focus?
That’s the basic premise behind Canon’s A-DEP mode. You use the system by picking a point in the foreground, then picking a point in the background, and refocusing one more time before you take the picture. A-DEP mode figures out exactly which aperture you need to use to get everything in between those two point in focus. This is the most efficient way to pick an aperture. It wastes the least amount of light.
Is it good for every photographic situation?
Arguably not. Some photographs don’t need to be taken with A-DEP mode. You can assume, for example, that you’ll want to use the smallest aperture possible for a landscape photo. In that case, you want to get everything in focus, not just whatever occurs between two points.
It’s also difficult to use A-DEP mode when you don’t have any other points of reference. A good example is a portrait of someone standing a few feet in front of a wall. Without anything behind or in front of the person (aside from the wall), you have no basis for figuring out the maximum depth-of-field necessary for the shot. You might as well just pick a wider aperture with the intent of blurring out some of the background.
Watch out - A-DEP is an automatic mode
A-DEP mode is an automatic mode, which means it doesn’t just pick the aperture for you. It also picks the shutter speed you’ll be using. A lot of photographers have expressed frustration with this because A-DEP will often pick a rather slow shutter speed when there isn’t much available light. Remember, at shutter speeds lower than 1/60s, there’s a strong risk of blur from camera shake.
If you’re going to use A-DEP mode in low light, be sure to bring a tripod or a flash. That’s your only guarantee of getting a shake-free image.
What results have you gotten with A-DEP mode? Was it useful, or did it just waste your time? Let me know.
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