Normal lens

In photography and cinematography, a normal lens is a lens that reproduces a field of view that generally looks "natural" to a human observer under normal viewing conditions, as compared with lenses with longer or shorter focal lengths which produce an expanded or contracted field of view that distorts the perspective when viewed from a normal viewing distance.^[1][2] Lenses of shorter focal length are called wide-angle lenses, while longer-focal-length lenses are referred to as long-focus lenses^[3] (with the most common of that type being the telephoto lenses).

For still photography, a lens with a focal length about equal to the diagonal size of the film or sensor format is considered to be a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal;^[2] this angle of view is about 53° diagonally. For cinematography, where the image is normally viewed at a greater distance, a lens with a focal length of roughly a quarter of the film or sensor diagonal is considered 'normal'. The term normal lens can also be used as a synonym for rectilinear lens. This is a completely different use of the term.

Typical normal focal lengths for different formats

Film still

Four "normal" lenses for the 35mm format.

Typical normal lenses for various film formats for photography are:

Film format	Image dimensions	Image diagonal	Normal lens focal length
9.5 mm Minox	8 × 11 mm	13.6 mm	15 mm
Half-frame	24 × 18 mm	30 mm	30 mm
APS C	16.7 × 25.1 mm	30.1 mm	28 mm, 30 mm
135, 35mm	24 × 36 mm	43.3 mm	40 mm, 50 mm, 55 mm
120/220, 6 × 4.5 (645)	56 × 42 mm	71.8 mm	75 mm
120/220, 6 × 6	56 × 56 mm	79.2 mm	80 mm
120/220, 6 × 7	56 × 68 mm	88.1 mm	90 mm
120/220, 6 × 9	56 × 84 mm	101.0 mm	105 mm
120/220, 6 × 12	56 × 112 mm	125.0 mm	120 mm
large format 4 × 5 sheet film	93 × 118 mm (image area)	150.2 mm	150 mm
large format 5 × 7 sheet film	120 × 170 mm (image area)	208.0 mm	210 mm
large format 8 × 10 sheet film	194 × 245 mm (image area)	312.5 mm	300 mm

For a 35 mm camera with a diagonal of 43 mm, the most commonly used normal lens is 50 mm, but focal lengths between about 40 and 58 mm are also considered normal. The 50 mm focal length was chosen by Oskar Barnack, the creator of the Leica camera.

Note that the angle of view depends on the aspect ratio as well; a "normal" lens on 35mm does not have the same view as a "normal" lens on 645, for example.

Digital still

In digital photography, the sensor "type" is not the sensor diameter:

(*) refers to TV tube diameters that were standards in the 50s. The normal lens focal length is roughly 2/3 of the TV tube diameter.

(**) this is a mathematical calculation because most of the cameras are equipped with zoom lenses.

Sensor type	TV-tube diameter *	Image dimensions	Image diagonal	Normal lens focal length **
1/3.6"	7.1 mm	3.0 × 4.0 mm	5.0 mm	5 mm
1/3.2"	7.9 mm	3.4 × 4.5 mm	5.7 mm	5.7 mm
1/3"	8.5 mm	3.6 × 4.8 mm	6.0 mm	6 mm
1/2.7"	9.4 mm	4.0 × 5.4 mm	6.7 mm	6.7 mm
1/2.5"	10.2 mm	4.3 × 5.8 mm	7.2 mm	7 mm
1/2"	12.7 mm	4.8 × 6.4 mm	8.0 mm	8 mm
1/1.8"	14.1 mm	5.3 × 7.2 mm	8.9 mm	9 mm
1/1.7"	14.9 mm	5.7 × 7.6 mm	9.5 mm	9.5 mm
2/3"	16.9 mm	6.6 × 8.8 mm	11.0 mm	11 mm
1"	25.4 mm	9.6 × 12.8 mm	16.0 mm	16 mm
Four Thirds[4]	33.9 mm	13 × 17.3 mm[5]	21.63 mm	22 mm
4/3"	33.9 mm	13.5 × 18.0 mm	22.5 mm	23 mm
APS-C	45.7 mm	15.1 × 22.7 mm	27.3 mm	27 mm
DX	n/a	15.8 × 23.7 mm	28.4 mm	28 mm
FF (35 mm film)	n/a	24 × 36 mm	43.3 mm	50 mm
(6 × 5 cm)	n/a	36.7 × 49.0 mm	61.2 mm

Cinema

In cinematography, a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal, since movies are typically viewed from a distance of about twice the screen diagonal.^[6]

Film format	Image dimensions	Image diagonal	Normal lens focal length
Standard 8	3.7 × 4.9 mm	6.11 mm	12–15 mm
Single-8 (FUJI)	4.2 × 6.2 mm	7.5 mm	15–17 mm
Super-8	4.2 × 6.2 mm	7.5 mm	15–17 mm
9.5 mm	6.5 × 8.5 mm	10.7 mm	20 mm
16 mm	7.5 × 10.3 mm	12.7 mm	25 mm
35 mm	18.0 × 24.0 mm	30.0 mm	60 mm
35 mm, sound	16.0 × 22.0 mm	27.2 mm	50 mm
65 mm	52.6 × 23.0 mm	57.4 mm	125 mm

References

1. Ernst Wildi (2001). Creating World-Class Photography: How Any Photographer Can Create Technically Flawless Photographs. Amherst Media, Inc. p. 44. ISBN 978-1-58428-052-1.
2. Leslie D. Stroebel (1999). View camera technique (7th ed.). Focal Press. pp. 135–140. ISBN 978-0-240-80345-6.
3. Bruce Warren, Photography, page 71
4. The Four Thirds Standard, Four Thirds Consortium, 2008, retrieved 2009-04-17
5. "No more compromises: the Four Thirds standard". Olympus Europa. Archived from the original on 2011-09-27.
6. Anton Wilson, Anton Wilson's Cinema Workshop, American Cinematographer, 2004 (Page 100) online.