Photographic Camera Homework Help, Assignment Help, Online Tutor, Tutoring

Submit Assignment

* *

Payment Online Assignment Help

Thermodynamics

Homework Help

sfsf

Photographic Camera

A photographic camera consists essentially of a convex lens, a light sensitive film or plate at the back and a focusing arrangement. There is an adjustable aperture known as diaphragm that permits different amounts of light to enter the camera.

The image is focused on the plate or film by altering the distance of the lens from it. There is a shutter placed in the path of light and the time for which it is opened depends upon the brightness of the object, the sensitivity of the photographic emulsion, the focal length of the lens and the size of the stop.

The diameter d of the stop is usually given as a fraction of the focal length ƒ of the lens system and the ratio (focal length/diameter of the stop) is called the ƒ-ratio or ƒ-number.

Suppose the focal length of the lens is 11 cm and the diameter of the stop is 1 cm. Then the ƒ-ratio or ƒ-number is 11 and d = ƒ/11.

The diameters of the stop of a camera are usually marked so that the exposure time is doubled between each position e.g.

Therefore, the ƒ-ratios are 5.6, 8, 11, 16, 22 etc. and their squares are in the ratio of 1:2 : 4:8 : 8:16.

Therefore, if the correct exposure for ƒ/5.6 is one second, then, for ƒ/8 it is 2 seconds and for ƒ/11 it is 4 seconds and so on.