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June 12, 2008
[THE BLEEDING OBVIOUS]
You are no doubt familiar with the concept of teaching Granny to suck eggs. According to our Encyclopaedia of Word and Phrase Origins it means to offer advice to someone who already knew how to do it before you were born.
So when a photographer of our acquaintance told us that he was having trouble getting satisfactory exposures with his expensive DSLR it never occurred to us to draw his attention to the exposure compensation button, right there under his nose on the camera body. This man has experience, so we assumed that he knew the function of the button marked with the + and – symbols.
However, when we said: “Well, we find that we can usually correct under or over exposure pretty easily with the exposure compensation function”, he said: “What’s that?”
Every digital camera that we have tested has either a button marked with a plus and minus sign, or something similar is accessible in the top layer of the menus. It is the most useful control on a camera.
Pressing it brings up a linear scale on one of the LCD screens, usually graduated in 1/3 EV intervals. Moving a secondary control up or down, or left or right (it varies from camera to camera) exposure is adjusted in a nonce – quickly enough to get a second chance at the shot.
On SLRs the steps can be varied, sometimes between 1/3 EV and 2 EV. (EV means “exposure value” and is a combination of f stop and shutter speed, and increasing an exposure by 1 EV may mean opening the aperture by one f stop or halving the shutter speed.)
In the days of film we took pot luck with exposures and had no idea of how things would turn out until we had the photos back from processing. Now we have instant review of images and that gives us the on-the-spot opportunity to do it again. And again, if necessary, until we get it right.
There a catch with exposure compensation. Once it has been dialled in, on most cameras, it stays set until it is manually reset. You will be caught out on occasion when you pick up the camera to take a quick photo and find that it is too dark or too light because you haven’t reset compensation since the last use.
While talking of exposure compensation, the other useful feature built into many digital cameras is auto bracketing. Using this function the camera takes three or more exposures in rapid succession, usually one under exposed, one over exposed and one at what the camera calculates is correct exposure.
Some cameras, such as the Pentax K20D and the Nikon D300 do even better. The Pentax will take up to seven exposures in a set and the Nikon will do nine. When you have nine exposures, made at 1/3 EV intervals, you have to be really unlucky not to get one that is spot on. Even with three exposures you improve your chances of getting it right, especially in a situation where the light confuses the camera’s meter.
The number of exposures in a bracket and the intervals between them are set in the menu system. The camera is set to high speed burst mode, and the shutter button is held down until the specified number of shots is taken and the camera stops firing.
Posted by terry at June 12, 2008 12:41 AM
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