APOGEE PHOTO MAGAZINE: Photography for Young People: The Reciprocity Rule

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Apogee Photo Magazine

Photography for Young People:
The Reciprocity Rule

By Matthew L. Kees

Using an f/16 setting on your camera will give you great depth of field and almost everything in your photo may be in focus.

Using the rule of reciprocity is the key to being a pro photographer. Your camera meter may indicate an exposure that works for the scene, but if you know the rule of reciprocity, you can choose a wide variety of exposure settings. The limits are the f/stop range of the lens and/or the fastest shutter speed on the camera body.

Reciprocity is when you add a "stop" of light entering the camera with one of the exposure controls (either the f/stop or shutter speed) and balance it by taking away a "stop" of light with the other.

A "stop" is a photographic term for twice or half the amount of light. It is the basic control used on all professional level cameras (those with f/stop and shutter speed settings). Both the f/stop and shutter speed controls can change the amount of light reaching the film in stops.

For example...

You are outdoors in bright light and the camera’s exposure meter (or light meter) indicates an exposure of f/16@1/125 for your 100 ISO film. You actually have many other choices for taking that picture. All of them will allow the same amount of light to reach the film and expose the film properly.

If your lens' smallest aperture is f/16, you will only have one direction you can go. You can let in one more stop of light by choosing f/11 on the lens and cut out a stop of light by using a 1/250 shutter speed. You now have an exposure with the exact same "Exposure Value" as the previous one, only your exposure settings have changed.

Using an f/4 setting on your camera creates a shallow depth of field and throws the background out of focus.

So, you may be asking yourself, why would I choose f/11@1/250 over f/16@1/125? Well, the f/stop controls something called Depth of Field, or how deep the focus is in the field of vision, and the shutter speed controls motion. Using an f/stop one stop away may not change the look of the final image that much, but what if we use our knowledge of reciprocity again and again?

We can open the lens another stop to f/8 and change the shutter speed to f/500 and again to f/5.6 and the shutter at 1/1000 and, if your camera has the 1/2000 shutter speed, we can use f/4@1/2000 and get exactly the same exposure value that we had from the original f/16@1/125 setting. Now the look of the finished image is greatly changed because f/4 has very little depth of field compared to f/16. The background of the picture taken at f/4@1/2000 will be soft, and the subject will be sharp and clear (if focused correctly). You have isolated your subject from the background - a very popular trick used in portrait photography. No longer is the background competing with the subject. You have successfully used the rule of reciprocity to change the look of your final image.

In both my private instruction classes in Hollywood and my online photo program I cover how to use reciprocity and depth of field on day 1. The first assignment is to shoot the same picture three times each using f/4, f/8 and f/16. When you get your prints back you are able to see how the changes in the aperture setting (or f/stop) affects the look of your pictures.

There are other factors relating to depth of field that I will cover in the next installment here at Apogee Photo Magazine. But for now, go out and shoot a few shots of the same subject using the reciprocity rule you learned today. It is the first step on the way to calling yourself a real professional photographer.

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If you are serious about becoming a professional photographer, or just want to take better pictures, please consider registering for my online photography program at www.MLKstudios.com. MLKstudios offers personal professional training from the comfort of home. We guarantee you will make great pictures!