Focal length and angle of view (0.1)

Requirement
1-3 photographs


Purpose
To establish by experiment the standard focal length of any camera, i.e. where the image in the viewfinder and what the naked eye sees are the same


Technical learning
The standard focal length of a lens produces an image which is of the same size as normal human vision. It varies by type of camera, i.e. it depends on the size of its sensor (digital) or film.


Exercise instructions
Point the camera at any scene. Shot 1 - with both eyes open, one looking through the viewfinder, the other directly at the scene. Set the focal length of the lens so that the size of the scene in the viewfinder is the same as what the other eye sees. Note the focal length. Shot 2 - use a wide angle lens on its shortest focal length to shoot the same scene from exactly the same spot. Shot 3 - repeat using a telephoto lens on its maximum focal length.


Images and Review 
The first signs of autumn - the single leaf of the cherry blossom tree turns red

Standard view - 62mm

Wide angle view 24mm

Telephoto - 135 mm

When holding prints of these 3 photographs against the scene, the relative distances of each to the eye so that the image and the real scene look the same size are:

• Standard view - about 2 feet (1 full arm length)
• Wide angle view - right in front of the eye (even then it is marginally smaller than real life)
• Telephoto - about 4 feet, give or take 6 inches