What happens when you decrease the f-stop number by one full stop?

What happens when you decrease the f-stop number by one full stop?

• A. It halves the amount of light hitting the sensor
• B. It changes focal length
• C. It stops motion blur
• D. It doubles the amount of light hitting the sensor

Answer: (D)

Lowering the f-stop number means opening the lens aperture wider. Each full-stop change doubles or halves the light that reaches the sensor, and opening the aperture by one stop let twice as much light in. So the exposure increases by a factor of two when you decrease the f-stop by one stop. The other ideas don’t fit: halving the light would happen if you close the aperture by one stop, changing the focal length isn’t about aperture, and motion blur is mainly affected by shutter speed, not aperture.

Lowering the f-stop number means opening the lens aperture wider. Each full-stop change doubles or halves the light that reaches the sensor, and opening the aperture by one stop let twice as much light in. So the exposure increases by a factor of two when you decrease the f-stop by one stop. The other ideas don’t fit: halving the light would happen if you close the aperture by one stop, changing the focal length isn’t about aperture, and motion blur is mainly affected by shutter speed, not aperture.