Lenses For SLR and DSLR Cameras - Focal Length and Angle of View

Focal Length and Angle of View

The focal length of a lens, together with the size of the image sensor in the camera (or size of the 35 mm film), determines the angle of view. A lens is considered to be a "normal lens", in terms of its angle of view on a camera, when its focal length is approximately equal to the diagonal dimension of the film format or image sensor format. The resulting diagonal angle of view of about 53 degrees is often said to approximate the angle of human vision; since the angle of view of a human eye is at least 140 degrees, more careful authors will qualify that, for example as "similar to the angle of crisp human vision." A wide-angle lens has a shorter focal length, and includes more of the viewed scene than a normal lens; a telephoto lens has a longer focal length, and images a small portion of the scene, making it seem closer.

Lenses are not labeled or sold according to their angle of view, but rather by their focal length, usually expressed in millimeters. But this specification is insufficient to compare lenses for different cameras because field of view also depends on the sensor size. For example, a 50 mm lens mounted on a Nikon D3 (a full-frame camera) provides approximately the same field of view as a 32 mm lens mounted on a Sony α 100 (an APS-C camera). Conversely, the same lens can produce different fields of view when mounted on different cameras. For example, a 35 mm lens mounted on a Canon EOS 5D (full-frame) provides a slightly wide-angle view, while the same lens mounted on a Canon EOS 400D (APS-C) provides a "normal" or slightly telephoto view.

In order to make it easier to compare lens–camera pairs, it is common to talk about their 35 mm equivalent focal length. For example, when talking about a 14 mm lens for a Four Thirds System camera, one would not only indicate that it had a focal length of 14 mm, but also that its "35 mm equivalent focal length" is 28 mm. This way of talking about lenses is not just limited to SLR and DSLR lenses; it is very common to see this focal length equivalency in the specification of the lens on a digicam.

Values in the following table are approximate, and apply to rectilinear lenses only, not to fisheye lenses.

Sensor size: 35 mm or full-frame APS-H APS-C Foveon X3 Four Thirds
Crop factor: 1.0 1.3 1.5 or 1.6 1.7 2.0
Lens view Angle of view
(deg. diagonal)
Focal length (mm)
Ultra wide-angle 118 13 10 8 8 7
111 15 12 10 9 8
100 18 14 12 11 9
92 21 16 14 12 11
Typical wide-angle 84 24 18 15 14 12
75 28 22 18 16 14
Slightly wide-angle 63 35 27 23 21 18
"Normal" 59–47 40–50 30–38 25–32 23–29 20–25
Portrait lens 29 85 65 55 50 43
23 105 81 68 62 53
Telephoto 18 135 104 87 79 68
14 180 138 116 106 90
12 210 162 135 134 105
Long telephoto 8 300 231 192 176 150
6 400 308 258 235 200
5 500 385 323 294 250
4 600 462 387 353 300
3 830 638 535 488 415
Very long telephoto 2 1200 923 774 706 600
Some cameras using
this sensor size:
35 mm film
Canon EOS-1Ds
Canon EOS-1Ds II
Canon EOS-1Ds III
Canon EOS-1D X
Canon EOS 5D
Canon EOS 5D Mark II
Canon EOS 5D Mark III
Canon EOS 6D
Nikon D3 (X, S), D4
Nikon D700, D800, D600
Sony α 850, α 900, α 99
Leica M9, M9-P, M Monochrom, M-E, M
Canon EOS-1D
Canon EOS-1D II N
Canon EOS-1D III
Canon EOS-1D IV
Kodak DCS 460 - 760
Leica M8
Canon EOS 7D
Canon EOS D30, D60
Canon EOS 10D - 60D
Canon EOS 300D - 1100D
Nikon D1 (H,X)
Nikon D2H (Hs,X,Xs)
Nikon D40 (x) - D90
Nikon D100 - D300
Nikon D3000-D7000
Pentax *ist D-Series
Pentax K10D - K200D
Pentax K-5, K-5 II, K-7, K-30
Pentax K-m, K-r, K-x
Sony α 33 - α 700 (except α 99)
Konica Minolta 5D, 7D
Sigma SD9
Sigma SD10
Sigma SD14
Sigma DP1
Sigma DP2
Canon EOS DCS 3
Leica Digilux 3
Olympus E-3
Olympus E-30
Olympus E-620
Panasonic DMC-G1

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