The exposure value, EV, of a photograph can be calculated from the time, t, in s

Question

The exposure value, EV, of a photograph can be calculated from the time, t, in seconds that the shutter was open and the value of the f-stop, f, the picture was taken at by using the logarithmic equation: EV=log2 f2/t

22. use the properties of logarithms to expand the formula for EV.

23. Keith takes a picture of a waterfall with a shutter speed of 1/60 second at f/5.657. he likes exposure of his picture, but he wants to leave the shutter open four times as long to better capture the motion of the water. What f-stop should he use on his next picture?

Explanation / Answer

EV = log 2 f^2 / t

22) applying properties of log to expand

EV = 2 log 2 (f )- log 2 (t )

23) EV = 2 log 2 ( 5.657 ) - log 2 ( 1/60)

EV = 10.906

10.906 = 2 log f - log 2 ( 4*1/60)

solving for f

f = 170

so, he should use f stop = 170

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