When taking an incident light reading, reducing light from f/4 to f/2.8 reduces the light by what percentage?

When taking an incident light reading, reducing light from f/4 to f/2.8 reduces the light by what percentage?

• A. 50%
• B. 25%
• C. 75%
• D. 100%

Answer: (A)

A single f-stop change either doubles or halves the amount of light reaching the sensor. Moving to a smaller f-number (a wider aperture) lets in more light, while moving to a larger f-number (a smaller aperture) reduces light. Going from f/4 to f/2.8 is one stop wider, so the light collected is about double — roughly a 100% increase. If a question is about reducing light by 50%, that would correspond to moving to a smaller aperture such as f/5.6, which halves the light. The wording in the prompt seems to describe a reduction, but the actual f/4 to f/2.8 change increases light by one stop.

A single f-stop change either doubles or halves the amount of light reaching the sensor. Moving to a smaller f-number (a wider aperture) lets in more light, while moving to a larger f-number (a smaller aperture) reduces light.

Going from f/4 to f/2.8 is one stop wider, so the light collected is about double — roughly a 100% increase. If a question is about reducing light by 50%, that would correspond to moving to a smaller aperture such as f/5.6, which halves the light. The wording in the prompt seems to describe a reduction, but the actual f/4 to f/2.8 change increases light by one stop.