If you stop down two stops from F4, which aperture do you reach?

• A. F4
• B. F8
• C. F5.6
• D. F11

Answer: (B)

Stopping down two stops means making the aperture smaller by two standard steps in the usual sequence of f-numbers. The common progression goes from f/4 to f/5.6 to f/8, with each step reducing the amount of light reaching the sensor by about half. So two steps from f/4 brings you to f/8. In terms of light, that’s a reduction to one quarter of the original exposure, which would require either a longer shutter speed or a wider aperture to compensate, but since we’re stopping down, the result is f/8. The other options don’t fit because f/4 is the starting point, f/5.6 is only one step down, and f/11 is three steps down from f/4.