The focal length is a distance from the optical center to the focal plane on which beams gather and the image is formed. It is measured in millimeters. Buying the camera, it is necessary to learn focal length of a lens as than it is more, that stronger the lens enlarges the image of a subject of shooting.
It is required to you
Instruction
1. The first way. The focal length can be found by means of formulas thin lens: 1/distance from a lens to subject +1/distance from a lens to the image =1/main focal length of a lens. From this formula express the main focal length of a lens. At you the following formula has to turn out: the main focal length of a lens = distance from a lens to an izobrazheniya*rasstoyaniye from a lens to a subject / (distance from a lens to the image + distance from a lens to a subject). Now count the size unknown to you by means of the calculator.
2. If before you not the thin, but thick lens, then a formula remains without change, but distances are counted not from the center of a lens, and from the main planes. For the valid image from the valid subject in the collecting lens accept focal length as size positive. If the lens disseminating - the focal length is negative.
3. The second way. The focal length can be found by means of an image scale formula: scale = focal length of a lens / (distance from a lens to the image - focal length of a lens) or scale = (distance from a lens to the image - focal length of a lens) / focal length of a lens. Having expressed focal length from this formula, you easily will count it.
4. The third way. The focal length can be found by means of a formula lens force =1/focal length. Let's express from this formula focal length: focal length =1/optical power. Count.
5. The fourth way. If you were given thickness of a lens and increase, then to find focal length, multiply them.
6. Now you know how to find focal length. Choose any given above-mentioned way depending on what is given you, and then you without effort solve the task set for you. Surely define what lens before you as the positive or negative value depends on it has focal length. And then you solve everything without uniform mistake.