Exposure increase for closeups

When you are shooting subjects very close up (using extension rings or bellows to get a sharp image), the image is less bright than with distant subjects - even though lighting and f-number remain the same. Inside the camera the effect is like being in a darkened room with a slide projector being moved away from the screen (the film). As you focus the camera lens for an ever-closer subject the image becomes bigger but also dimmer.

If your camera measures exposure through the lens itself this change is taken into account by the metering system, but when using a separate meter you must increase the exposure it reads out. In practice the increase starts to become significant when you focus on a subject closer than about five times the focal length of the lens you are using, growing greater as you focus on subjects closer still, e.g. something 250 mm from a 50 mm lens needs only 1M times the normal exposure; at 170 mm it requires twice, and at 100 mm four times the exposure the handmeter shows. To calculate exposure increase multiply the exposure shown on the meter by (M + 1)2, where M is magnification, meaning height of image divided by height of subject.

For example, photographing a 30 mm high postage stamp so that it appears 12 mm high on the film. As magnification is 0.4 you must multiply exposure by 1.42 which is 2. You can increase exposure either by giving a slower shutter speed, or by opening up the aperture - one f-number for a x 2 increase, one and a half for x 3, and so on.

Digital Cameras For Beginners

Digital Cameras For Beginners

Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.

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