The Reciprocal Rule in Photography

This might be a lesser known tidbit about when to use or not to use a tripod. It all depends on the focal length of your lens. As a guide, you should be sure that your shutter speed is at or faster than the reciprocal of you focal length – otherwise use a tripod to be safe and avoid camera shake.

So…if the focal length on the lens is set to 50mm AND you’re using a full-frame (such as a Mark II) or 35mm film camera, then you would need a shutter speed of 1/50 or faster [50/1 = 1/50]. If you’re camera has a crop factor like the x1.6 crop on most Canons or the x1.5 crop on Nikons then you multiply the focal length the lens is set to by the crop factor number and THEN use the reciprocal of that number [50mm: 50 x 1.6 = 80 = 80/1 = 1/80].