If photographer has camera with convex length 50mm lens is able to be moved relative to film plane.?

Question

moving allows the lense-film distance to vary between 50mm and 70mm. how can i find the range of objects distances for which the camera can give a sharp image on film. I also need to find the linear magnification? arg any suggestions would be greatly appreciated

Answer 1

If the lens-film distance is 5 cm., and the focal length is 5 cm, the object distance is u cm. where:

1 / u + 1 / 5 = 1 / 5

u can be infinite.

For lens-film distance 7cm, the object distance is u cm. where:

1 / u + 1 / 7 = 1 / 5

u = 17.5 cm.

The range is from 17.5 cm. to infinity.

When the object distance is u and the image distance is v, the magnification is v / u.

When u is infinite, the magnification is 0.

When u is 17.5 cm, the magnification is 7 / 17.5 = 0.4.