A good photograph is taken with (1/15) second and f/2 with ISO 100. To capture a

Question

A good photograph is taken with (1/15) second and f/2 with ISO 100. To capture a fast moving car you change the exposure time to (1/250) second, which is the shortest exposure time that your cheap camera can provide. To make up fo rthe lost amount of light on the film, you can now either change the ISO or the f/, but both have drawbacks: you do not wish to decrease your depth of field too much, nor the resolution of the photograph, so you decide to compromise and change a bit of both the ISO and the f/. In order to provide the same amount of "more light" on the film from both, what are the new ISO and f/?

Explanation / Answer

amount of light in the first case = exposure time*iso*1/aperture

amount of light in the 1st and 2nd case must be equal therefore

1/15*2*100=1/250*iso*x

the aperture must be less than 2 as the exposure time is less more aperture is required for capturing more light

iso*x=10000/3

for the picture not to be so grainy the iso must not be kept too large....

we can see that for an iso 0f 2000 and x of 5/3 we get the same amount of light

there are no ranges of iso between 1600 and 2000

so we had to take an iso of 2000 for which we get 3f/5 aperture

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