A little about camera exposure

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Part of the fun of photography is the enjoyment you get from having a fine piece of equipment in your hands, knowing how to use it, and anticipating the creative results you will get with it. Sometimes, the challenge of using it to its full advantage is compromised by your eagerness to use it before you have learned what all the controls are for.

It all started with the alphabet code letters “AE” (Auto Exposure) about 30 years ago. That was the beginning of a new era in photography because proper exposure at that time was the biggest problem anybody had to overcome. All you had was Manual mode. You either followed instructions on the film information sheet and set the shutter/aperture according to the sky condition, or you bought an expensive exposure meter and learned how to use it.

The Canon AE-1 solved that problem, and, in doing so, became very popular. The percentage of pictures per roll that “turned out” improved tremendously, and the word spread. The nose of the camel was in the tent!

What followed were priority modes, such as Aperture priority (“A”), designed to maintain a selected aperture, and control depth of field. However, this requires the program to automatically alter shutter speed in order to control exposure. The benefit: tack sharp pictures from 3 feet to infinity at f16, or beautiful portraits with out-of-focus backgrounds at f5.6. The downside of this is you may have to use a tripod at small apertures (f16) to avoid the problems associated with slow shutter speeds.

The next mode was “S,” for Shutter priority. This feature will maintain a selected shutter speed by changing the aperture to control exposure. The benefits are beautifully blurred water at slow shutter speeds (1/2 a second to 1/40th of a second), or, in the case of sports, frozen motion at high shutter speeds (1/250th of a second to 1/1,000th of a second).

You have to be careful when you use high shutter speeds. Your depth of field will be shallow with large apertures. The problem is minor with wide-angle lenses, but requires careful consideration when using longer lenses. Again, you may have to use a tripod to avoid the problems associated with slow shutter speeds.

In Program mode, the camera picks the best combination of shutter speed and aperture for the light condition, in accordance with a predetermined program. The program starts with a standard bright sunlight exposure at midday (100 asa, f11 at 1/100th of a second, the rule of ones) and provides more exposure incrementally as light diminishes (100 asa, f8 at 1/50th is two “stops” more exposure, for example). The benefit to the photographer is a properly exposed image. However, there is no control over depth of field and motion. Frequently, the pictures betray the fact that they were taken in Program mode, with such faults as out of focus backgrounds in scenics, or blurred action shots in a soccer game. It’s good to know how to take pictures in Manual mode because it gives you a solid foundation in the relationships between shutter speed, f stop, focus and depth of field, etc. However, when you have all of the features and tools now available in the average camera and digital darkroom, and know how to use them, you are free to concentrate on recreation of personal visual expressions in your photographs. And, rather than dealing with the distractions of maintaining focus, adjusting exposure or checking depth of field, you look at the scene, compose the picture, and capture the image.




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