Another common method of taking close-up pictures involves extension tubes or a bellows. Such a device fits between the lens and the camera body to let you make sharp pictures at close distances. Since an extension device fits between the lens and the camera body, you can use it only on a camera that accepts interchangeable lenses, which includes most SLR cameras.

Since the tubes or a bellows moves the lens farther from the film than it would be for normal picture-taking, you must compensate for the light loss by using a larger lens opening or a slower shutter speed. Cameras with built-in meters do this automatically. The longer the extension, the greater the exposure increase.

If you have an older camera that lacks a built-in meter, you can use the exposure compensation chart to determine how much to increase the exposure.

To use the chart, first calculate the magnification by using the formula m = d/f, where m = magnification, d = length of bellows extension or extension tube in millimetres, and f = lens focal length in millimetres.

To determine a value for "d" measure the distance from the film plane to the front of the lens in millimetres. Take the distance measurement "d" and the lens focal length "f" and put them into the above formula.

For example if d = 77 mm and f = 55 mm, then 77/55 = 1.4.

Take 1.4, the value of "m," and find it under magnification in the exposure compensation chart. Then multiply the shutter speed or increase the aperture by the number in the columns below the magnification.