There's a simple formula to calculate the correct shutter speed for any given lens, called the '500-rule'.
There's a simple formula to calculate the correct shutter speed for any given lens, called the '500-rule'. In its simplest form, this is 500 divided by the focal length of your lens. For example, if you are using a 20mm lens, this would be 500 / 20mm = 25 seconds. This, however, only applies to full-frame cameras.