Ansel Adams said, “There is nothing worse than a brilliant image of a fuzzy concept.” While I certainly agree with Adams’ sentiment, if your photo is out of focus, no one will care about your image.Today’s digital cameras, whether expensive DSLRs or low end Point & Shoots all have remarkably accurate automatic focus capability, but sometimes, your image composition, or conditions which are a bit out of the ordinary, can defeat any camera’s auto-focus.
In Part 1, I discuss how auto-focus works, and many of the modes of auto-focus found in today’s camera’s. In Part 2, I’ll discuss how to use auto-focus, difficult auto-focus situations, and when to manually focus your camera if it has that capability.In auto-focus, the camera senses the difference in contrast between the edges of objects as seen through the lens. When the subject has sharp contrast differences, the camera will probably easily and correctly focus. If the edges of your subject are fuzzy, or aren’t clearly distinguishable from the surrounding background, the camera will have difficultly focusing, if it can at all. When this occurs, the camera’s auto-focus system will keep searching to find a clear sharp edge. This is sometimes called hunting.
Usually, in brightly lit conditions where the subject’s color makes it stand out from the background, auto-focus has little problem. If the light is dim, or the subject is similar in color to the background then auto-focus probably won’t work. Likewise, if your subject has multiple line patterns, it may have too many edges and the auto-focus system may not be able to decide on one to use, and therefore hunt. The same thing happens when there are many objects in the focus area.Recently, at a forum I frequent, a photog new to his DSLR told us how he tried to take a photo of a coyote about 100 yards away. He was trying to understand why his photograph was out of focus. The problem was the image was monochromatic, with the coyote blending into the background. In addition, in the overall landscape the coyote wasn’t much more than a blip. The camera’s auto-focus really didn’t have a chance. The photog needed to manually focus in this situation.
Auto-focus has a number of methods or modes it uses to determine at what distance from the camera it should focus the lens to produce a sharp image. The modes have different names, according to the type of camera and brand. I’ll briefly discuss the major modes.Face Detect:
The camera automatically detects the location of faces in the photo and focuses on them. If you’re taking a photograph of a single individual, or a small group of individuals in a single row, or “scrunched” together, I’ve found this mode works exceedingly well, especially on newer cameras.
The mode has difficulty when you’re photographing people of different complexions, and large groups in multiple rows or at tables, as they depend on depth of field and the photographer doesn’t control the actual point of focus.
Dynamic Area (No Frame):
The camera uses information from multiple focus points in a specific area of the image to determine focus. This mode is especially suited to continuous focusing, for action photographs. In this mode, the camera gets to choose the primary focus point in the focus area, not the photographer, which can be a problem.
This mode is similar to the Dynamic Area mode. It uses multiple focus points in a specific area of the image to determine focus, but unlike Dynamic Area focus, the photographer chooses the primary focus point within the focus area. This mode is especially suited to continuous focusing, when shooting action photographs.
Closest Subject Priority:
In this mode the camera focuses on the closest object of significant size in the image. The problem with this mode is when the closest subject is not the main subject and the camera focuses on the wrong part of the image. I never recommend this mode.
In this mode, the photographer chooses which focus point among all the available focus points for the camera to set the focus. In some cameras, it’s always the center focus point. This is an excellent mode for portraits or any photograph in which your subject(s) are stationary.
For many amateur photographers, Face Detect mode can be extremely helpful in taking photographs of groups, as long as you understand its shortcomings.
I never utilize Dynamic Area focus due to its uncertainty, but do use its cousin, Group Dynamic focus, when I’m using continuous focusing for action photographs.
For stationary subjects, I use Single Area mode, and use the focus point which matches the location of where I want to focus in the photograph, or I use the center focus point (more often than not), focus, then recompose my image to get the precise composition of the image I desire.
Part 2 next week.