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How to determine the focal length of group of lenses?

In: Cameras, Photography, Telescopes [Edit categories]

Answer:

Measure the distance from the center of the lens to the area where it 1.)Produces a clear image of very distant objects, 2.) The Sun (Be careful!), 3.) The Moon, 4.) A bright star or planet.

The source needs to be at or near infinity. If you use a light source that is close to the lens, your results will not be accurate. Of course, if you know the F ratio, you have it! An F/2 lens will be twice the diameter of the lens. An F/10 will be ten times, etc.

First answer by N4CUZ1. Last edit by N4CUZ1. Contributor trust: 3 [recommend contributor ]. Question popularity: 2 [recommend question].

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