Question

The camera lens has an aperture of f and the exposure time is (1/60)s. What will be the new exposure time if the aperture become 1.4 f ?

• A. $\frac{1}{46}$
• B. $\frac{1}{56}$
• C. $\frac{1}{72}$
• D. $\frac{1}{31}$

Answer 1

The correct option is D $\frac{1}{31}$

Aperture =f=f, Exposure Time 160160 sec.
Area of aperture =f2=f2,

Area α Exposure Timeα1exposuretime
New aperture =1.4f=1.4f area =1.96f2=1.96f2
Ratio of areas =1.96=1.96. Since area of aperture has increased thus exposure time will decrease in same proportion, i.e.,
New time =1(60/1.96)=131sec.=1(60/1.96)=131sec