Question

Turning the barrel of a 50-mm-focal-length lens on a manual-focus camera moves the lens closer to or farther from the sensor to focus on objects at different distances. The lens has a stated range of focus from 0.70 m infinity.
How far does the lens move between these two extremes?

Answer 1

Answer:

Explanation:

To focus object at .7m , the image distance can be measured as follows

object distance u = .7m

focal length f = .05 m

image distance v = ?

from lens formula

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

$\frac{1}{v} +\frac{1}{.7} = \frac{1}{.05}$

$\frac{1}{v} =\frac{1}{.05} -\frac{1}{.7}$

v = .054 m

= 54 mm

when the object is at infinity , image is formed at focus ie at distance of

50 mm .

So lens position from sensor  where image is formed , varies from 54 mm to 50 mm .