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Editor's note: This excerpt first appeared in photographer and author Harold Davis' recent Focal Press book, Photographing Flowers: Exploring Macro Photography with Harold Davis.
The closer you...
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.
