The reciprocal rule, simply is about how to make sure when hand holding your camera, that your images are sharp. It’s quite simple your shutter speed should be at least “1” over your lens focal length. In other words, to keep your shots sharp, you should use a shutter speed that is the reciprocal of your lens, otherwise, you’re at risk of blur due to camera shake.
As an example, using a 50mm lens, you’ll need a shutter speed of at least 1/50s. And if you use a 200mm lens, you’ll need a shutter speed of at least 1/200s.
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