How to find the focal length of lens?

nightcheese

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So I'm a beginner when it comes to photography; I know the general terms like aperture, shutter speed etc, but someone asked me what the length of my lens was for my recently purchased Konica Autoreflex T3, and I have no idea on how to find it.
 

Jeff15

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Hello and welcome, the focal length of your lens will be printed on the lens..
 

Gary A.

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Per Nikon:
"Focal length, usually represented in millimeters (mm), is the basic description of a photographic lens. It is not a measurement of the actual length of a lens, but a calculation of an optical distance from the point where light rays converge to form a sharp image of an object to the digital sensor or 35mm film at the focal plane in the camera. The focal length of a lens is determined when the lens is focused at infinity.

The focal length tells us the angle of view—how much of the scene will be captured—and the magnification—how large individual elements will be. The longer the focal length, the narrower the angle of view and the higher the magnification. The shorter the focal length, the wider the angle of view and the lower the magnification."

Typically, the focal length is printed on the front of the lens and is represented in mm but sometimes in cm. A normal lens for a 35mm film camera is 50mm.
 

KmH

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The lens focal length is in mm.
50 mm is a common lens focal length.
Prime lenses have just 1 focal length.
Zoom lens will have a focal length range printed on them like 18-55 mm, 24-85 mm, or 70-200 mm.

Other numbers on the lens define the maximum lens aperture - like f/1.8, for a prime lens, or for a zoom lens a range of maximum apertures that change automatically as the focal length of the lens is zoomed out or in.
 

petrochemist

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Most lenses have the focal length & aperture written round the front of the lens - as a range for zooms.
If you look at the EXIF information that's stored as part of any images you capture the focal length etc will also be included there too.

I have a few lenses that were not intended for photography, and have to some experiments to find out their focal length. For a simple lens distant object such as the sun the image is formed at the focal length, but many photographic lenses are more complex using telephoto or retrofocal designs to change this (without these tricks long lenses would be longer & short focal length lenses wouldn't work with SLRs...)
 

480sparky

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...............If you look at the EXIF information that's stored as part of any images you capture the focal length etc will also be included there too...........

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........... someone asked me what the length of my lens was for my recently purchased Konica Autoreflex T3,................
 

jamescooper18

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Focal length is the basic description of a photographic lens that expressed in millimeters. It does not mean the actual length of a lens. It’s a calculation of an optical distance from the point where light rays meet to configuration a configure a sharp image of an object to the digital sensor or 35mm film at the focal plane in the camera. In a word, the focal length of a lens is determined when the lens is focused at infinity.
 

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