Question

How far in mm) from the lens must the film in a camera be, if the lens has a 38.0 mm focal length and is being used to photograph a flower 65.0 cm away? mm

Answer 1

focal length, f= 38.0 mm

distance of object = 65.0 cm = 650 mm

image distance from lens can be calculated by using lens formula

$\frac{1}{v} = \frac{1}{f}+ \frac{1}{u}$

  $= \frac{1}{38}+ \frac{1}{-650}$

solving we get,

$v=$ 40.4 mm

Therefore film must be at a distance of 40.4 mm from the lens.