A Site for Photographers by Photographers

Home > Equipment > Equivalent Lens Focal Lengths For Different Film Sizes

Featured Equipment Deals

Conservation Photography: The Power of Pictures Read More

Conservation Photography: The Power of Pictures

On Earth Day, wildlife photographer Chris Weston explains how photographs have the power to bring people together and create change.

Latest Equipment Articles

The Week in Photography News Read More

The Week in Photography News

November 15-21, 2014: Hear the latest goings-on in the photography world, from product releases to event and campaign announcements and more.

Latest Learning Articles

Introduction to Creating an Album in Lightroom - Part I (Video Tutorial) Read More

Introduction to Creating an Album in Lightroom - Part I (Video Tutorial)

Learn to create an album in the Book Tab of Lightroom that you can publish and present to clients.


Equivalent Lens Focal Lengths For Different Film Sizes

by Ed Scott, 1996


Photographers usually are most familiar with one camera format, typically 35 mm. They have a good feel for the angle of coverage of lenses in this familiar format but find that their instincts fail them when they switch to a different size film. The following table shows which lenses provide equivalent angles of coverage among film formats.

Determining the 35 mm focal length equivalent for a 2 1/4 Square format camera lens is an apples to oranges comparison unless you set some specifications for framing and print aspect ratio. Once you do that, the principle of similar triangles makes it quite easy to calculate. Here is a table of 35 mm lens equivalences for various Hasselblad lens listed in terms of equivalent angle of coverage for the specified print aspect ratio conditions:

35 mm Equivalents For Hasselblad (2 1/4 Square) Camera Lenses
6x6 cm Lens Largest Square Largest 8 X 10 Largest 11 X 14 Full 35 mm
40 mm 17.3 mm 21.6 mm 22.0 mm 26.0mm
50 mm 21.6 mm 27.1 mm 27.6 mm 32.6mm
60 mm 26.0 mm 32.5 mm 33.1 mm 39.1mm
80 mm 34.6 mm 43.3 mm 44.1 mm 52.1mm
120 mm 51.9 mm 64.9 mm 66.1 mm 78.1mm
150 mm 64.9 mm 81.2 mm 82.7 mm 97.7mm
180 mm 77.9 mm 97.4 mm 99.2 mm 117 mm
250 mm 108 mm 135 mm 138 mm 163 mm
350 mm 151 mm 189 mm 193 mm 228 mm
500 mm 216 mm 271 mm 276 mm 326 mm
FACTOR 0.433 0.541 0.551 0.651

These calculations are based upon stock Hasselblad 120 mm and Nikon 35 mm film apertures. The Hasselblad aperture measures 2.15 inches square. The Nikon aperture measures 0.93 inches high by 1.40 inches wide.

  • The factor for largest square is calculated as follows: 0.93 inches / 2.15 inches = 0.433
  • The factor for largest 8 X 10 is calculated as follows: ((0.93 inches / 8 inches) X 10 inches) / 2.15 inches = 0.541
  • The factor for largest 11 X 14 is calculated as follows: ((0.93 inches / 11 inches) X 14 inches) / 2.15 inches = 0.551
  • And finally, the factor for full 35 mm frame is calculated as follows: 1.40 inches / 2.15 inches = 0.651

These lens conversion factors can be used to find the 35 mm equivalent focal length of unlisted 2 1/4 Square format lenses. Just multiply the 2 1/4 Square format lens focal length by the appropriote factor to get its 35 mm equivalent focal lenth.

The same method can be used to compare 4x5 view camera lenses with 35 mm focal lengths.

35 mm Lens Equivalents For 4x5 View Camera Lenses
4x5 Lens Largest 8x10 Largest 11x14 Full 35 mm
90 mm 22.4 mm 22.8 mm 26.9 mm
127 mm 31.62 mm 32.1 mm 38.0 mm
135 mm 33.6 mm 34.2 mm 40.4 mm
150 mm 37.4 mm 38.0 mm 44.9 mm
210 mm 52.3 mm 53.1 mm 62.8 mm
240 mm 59.8 mm 60.7 mm 71.8 mm
300 mm 74.7 mm 75.9 mm 89.7 mm
500 mm 125 mm 127 mm 150 mm
800 mm 199 mm 202 mm 239 mm
1000 mm 249 mm 253 mm 299 mm
2000 mm 498 mm 506 mm 598 mm
FACTOR 0.249 0.253 0.299

Note: To use this table with an 8x10 view camera either divide the 35 mm lens focal lengths by 2 or multiply the 4x5 lens focal lengths by 2.

The 4x5 lens calculations are based upon a film holder aperture of 3.74 inches by 4.68 inches.

  • The factor for largest 8 x 10 is calculated as follows: 0.93 inches / 3.74 inches = 0.249
  • The factor for largest 11 x 14 is calculated as follows: ((0.93 inches / 11 inches) x 14 inches) / 4.68 inches = 0.253
  • The factor for full 35 mm format is calculated as follows: 1.40 inches / 4.68 inches = 0.299

The traditional definition of a normal lens is that its focal length is equivalent to the film diagonal length. In the case of a 2 1/4 Square format it might be useful to modify this definition to specify the largest 8x10 print area of the 2 1/4 film aperture (which coincidentally is closer to 80 millimeters than the square's diagonal). A normal lens typically has an angle of coverage of about 50 to 55 degrees and is roughly comparable to the useful or working angle of coverage of human vision (the peripheral vision areas serving mostly as a motion detection system).

Comparing lens focal lengths between formats in this way assures equivalent angles of coverage for ultimate print aspect ratio. It is easy to see that 80 mm and 150 mm lenses are normal focal lengths for 2 1/4 Square and 4x5 formats respectively. You can also see that 180 mm and 300 mm lenses are ideal portrait focal lengths for 2 1/4 Square and 4x5 view camera formats.

More


Copyright 1996 Ed Scott; images copyright 1991-2000 Philip Greenspun.

Article created 1996