[Below is the second part of a two part article about how to use the different exposure methods that are available on many P&S digital cameras. The aim is to explain the usefulness of each of the modes that come standard on most P&S cameras while taking away some of the panic you might feel about programming your P&S camera. So, if you're looking to learn more about these modes, then read on.]
In the first installment of this article (Don't Be Afraid; They Won't Bite: M, P, and S Exposure Modes Demystified), I provided an introduction to the different exposure modes (or manual modes) that are available on digital cameras. I covered the "P" (programmed auto), "M" (full manual), and "S" (shutter priority) modes in more depth, but left the description of my favorite mode for this installment.
We come now to "A" or "aperture priority" mode, which is my particular favorite. I primarily shoot DSLRs, but I have three point and shoot (P&S) cameras, and "A" is my usual mode if I'm using one of these cameras. In aperture priority mode, the shooter sets the desired aperture and the camera selects a shutter speed to produce the proper exposure. Aperture priority is less apt to run into the exposure problems that may occur in "S" mode at slow or fast shutter speeds because the shutter speed is dependent upon the aperture. Many P&S digital cameras offer a range of shutter speeds from several seconds to 1/3000th of a second or even higher -- this offers more latitude to produce a good exposure than designating a shutter speed in "S" mode where the apertures available may be limited. With "A", even if your aperture choices are limited, you're still selecting an available aperture and depending on the camera to find a shutter speed from that much broader range to produce a good exposure. In "S" mode you're arbitrarily selecting a shutter speed that may or may not be able to produce a good exposure due to limited aperture availability. This is not to say you can't make a bad picture with "A" mode -- if you set the camera for 1600 ISO, maximum aperture, and try to take a picture of a polar bear on an ice field on a sunny day, there's a good chance the camera's shutter speeds may not be fast enough and you'll over-expose. Conversely, if you set for 100 ISO, minimum aperture, and try to shoot a black cat in a coal bin at midnight without a flash, don't be surprised if the photo comes out dark. Just as with "M" or "S", most cameras will let you make a bad exposure with "A", but you have to work a little harder to do so.
"A" mode is the quickest way to set the fastest or slowest shutter speed available under any given set of conditions. If you want the fastest shutter speed, set the aperture to the lowest f number available. If you want the slowest shutter speed, set the aperture to the highest f number available. "A" mode also has the additional advantage of allowing you to maximize or minimize depth of field on any given shot.
In photo AP 1 (below), I set maximum aperture, f/2.8, to get the fastest possible shutter speed that would produce a good exposure. The camera set the shutter speed at about 1/900th of a second, and the water appears somewhat stopped or "frozen", which is the effect I sought.
AP 1 (view large image)
In photo AP 2, I set minimum aperture, f/8, to get the slowest shutter speed and the camera came up with about 1/150th of a second, which gives the water a much softer, flowing look that I wanted.
AP 2 (view large image)
Both photos look about the same exposure-wise, but the appearance of the moving water is changed depending on the shutter speed. Both photos could have been done in "S" mode, but it would have taken longer to come up with the exact shutter speed that would cause the camera to select the minimum and maximum apertures.
"A" is also your primary tool to minimize or maximize depth of field (DOF) on any particular shot. Depth of field (an area in the picture both in front of and behind the actual point of focus that appears reasonably sharp to the eye) is directly affected by aperture -- minimum apertures (higher f/numbers) produce more depth of field, maximum apertures (lower f/numbers) produce less depth of field. Depth of field also appears more pronounced at wider lens focal lengths -- pictures taken with your lens set at 35mm will show more depth of field than with the lens zoomed out to 300mm, all else being equal.
As a photographer, there may be occasions when you wish to minimize or maximize depth of field to affect the look of an image. Photo DOF 72 (below) was taken at minimum aperture (f/8) and about 1/250th of a second, DOF 73 (below) at maximum aperture (f/2.8) and about 1/1100th of a second. Both photos look about the same exposure-wise, and because the leaves in the foreground, which were the point of focus, aren't moving, they look about the same also despite the difference in shutter speed. However, when you look closely at DOF 72, the background appears sharper than in DOF 73. The blue flowers in the background are much clearer in 72 than 73.
Photo DOF 72 (view large image)
Photo DOF 73 (view large image)
Does the sharper background in 72 really change the image in comparison to 73? Try this quick test and see:
Maximize one of the photos on your screen and then close your eyes for a few seconds. Open your eyes and note where you immediately look on the photo. Do the same with the other photo.
My attention on DOF 72 is on the foreground leaves for a split second, then jumps to the blue flowers. It wants to go back and forth between the two. On DOF 73, it tends to stay with the leaves.
It's a matter of personal choice which look you prefer, but minimizing depth of field can have the effect of making the main subject in the photograph appear to stand out more in front of a blurrier background. If instead of leaves we took a portrait of a friend, we very well might want the background as blurry as possible to make our friend stand out from the background. But if the shot was of our friend standing on the edge of the Grand Canyon, we'd probably want both the friend and the Canyon as sharp as we could get.
A last consideration if you choose to dabble with the "P", "M", "S" or "A" modes: set your ISO to a fixed value rather than "auto". After all, you're exerting a little creative influence on your shots, and if the camera is free to choose the ISO you may find your desired results are being compromised.
Digital point and shoot cameras in "auto" mode offer a quick and easy way to make terrific images, but the next time you're just shooting for fun, try using the modes that invite a little more photographer participation. Anyone contemplating moving on to a DSLR someday can only benefit by shooting in the "M", "S", or "A" modes with their P&S, but folks who never intend to give up their P&S can expand their creative boundaries as well. Happy shooting!