Question

If a camera lens gives the proper exposure for a photograph at a shutter speed of 1/200 s at an f-stop of f/2.80, the proper shutter speed at f/7.92 is

Answer 1

Answer:

$\dfrac{1}{28.15432}\ s$

Explanation:

The factor by which the shutter speed is increased is $\dfrac{7.92}{2.8}$

Exposure time will be increased by

$f=2^{\dfrac{7.92}{2.8}}=7.1037\ s$

The proper shutter speed is given by

$\dfrac{1}{T}f=\dfrac{1}{200}\times 2^{\dfrac{7.92}{2.8}}=\dfrac{1}{\dfrac{200}{2^{\dfrac{7.92}{2.8}}}}\\ =\dfrac{1}{28.15432}\ s$

The proper shutter speed is $\dfrac{1}{28.15432}\ s$