Question

The exposure index EI for a 35 millimeter camera is a measurement of the amount of light that hits the film. It is determined by the equation EI = log₂(f₂/t) where f is the “f-stop” setting on the camera, and t is the exposure time in seconds. Suppose the f-stop setting is 8 and the desired exposure time is 2 seconds. What will the resulting exposure index be?

Answer 1

Consider the exposure index EI for 35 millimeter camera is a measurement of amount of light that hits the film is determined by following equation;

EI = log2(f2/t)

 

Suppose the f-stop setting is f = 8 and the desired exposure time is t = 2 seconds.

Substitute the known value as follows:

EI = log2(82/2)

 

Simplify as follows:

EI = log2(64/2)

    = log2(32)

 

Rewrite 32 in power- base form 32 = 52 as follows:

log2(32) = log2(25)

 

Use the logarithmic rule, loga(xb) = b∙loga(x) as follows:

log2(25) = 5log2(2)

 

Use the logarithmic rule, loga(a) = 1 as follows:

5log2(2) = 5(1)

               = 5

 

Therefore, the resulting exposure index is 5 millimeter.

Therefore, the resulting exposure index is 5 millimeter.