(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

using the same film and level of illumination two pictures are taken, one with double the f number of the other. for both films to recieve the same total light energy, what factor must the required time of exposure change for the picture with double the f number.

2. Relevant equations

f number = focal length/diameter

3. The attempt at a solution

double the f number couldbe taken as meaning half the diamter. therefore i can guess the answer should be a factor of two. but the f number formula doesn't relate 'total light energy' to anything does it? i thought it was a rating of light intensity.??

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: F number and light intensity

**Physics Forums | Science Articles, Homework Help, Discussion**