645 film crop factor and field of view calculator
A 645 film sensor measures 56 by 41.5 mm, a diagonal of 69.70 mm. Against the full-frame diagonal of 43.27 mm that is a crop factor of 0.621.
The diagonal divided by this gives the acceptable blur circle. 1500 is the usual modern figure.
- Full-frame equivalent focal length
- 21.73
- Equivalent aperture for depth of field
- 1.738
- Sensor diagonal
- 69.701
- Sensor area
- 2324.00 mm2
- Full frame gathers this many times more light
- 0.372
- Horizontal field of view
- 77.320 degrees
- Vertical field of view
- 61.324 degrees
- Diagonal field of view
- 89.755 degrees
- Hyperfocal distance
- 9450
- Depth of field
- 2088
- Frame width at the subject
- 4.800
Show the working
- Focal length = 35
- Aperture f-number = 2.8
- Subject distance = 3
- Circle of confusion divisor = 1500
- sensor_w = 56 = 56
- sensor_h = 41.5 = 41.5
- Sensor diagonal = hypot(56, 41.5) = 69.7011
- Crop factor = 69.7011 > 0 ? 43.266615305567875 / 69.7011 : 0 = 0.620 745
- Full-frame equivalent focal length = 35 * 0.620 745 = 21.7261
- Equivalent aperture for depth of field = 2.8 * 0.620 745 = 1.738 09
- Sensor area = 56 * 41.5 = 2324
- Full frame gathers this many times more light = 2324 > 0 ? 864 / 2324 : 0 = 0.371 773
- Horizontal field of view = deg(2 * atan(56 / (2 * 35))) = 77.3196
- Vertical field of view = deg(2 * atan(41.5 / (2 * 35))) = 61.3238
- Diagonal field of view = deg(2 * atan(69.7011 / (2 * 35))) = 89.7549
- coc = 69.7011 / 1500 = 0.046 467 4
- Hyperfocal distance = 35^2 / (2.8 * 0.046 467 4) + 35 = 9450.2
- near = 3*1000 * 9450.2 / (9450.2 + (3*1000 - 35)) = 2283.54
- far = 3*1000 < 9450.2 ? 3*1000 * 9450.2 / (9450.2 - (3*1000 - 35)) : 1e9 = 4371.59
- Depth of field = 4371.59 >= 1e9 ? 1e9 : 4371.59 - 2283.54 = 2088.05
- Frame width at the subject = 35 > 0 ? 3 * 56 / 35 : 0 = 4.8
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- crop factor = full-frame diagonal / sensor diagonal
- field of view = 2 arctan(sensor dimension / 2 focal length)
- hyperfocal distance = f^2 / (N c) + f
- equivalent aperture = aperture x crop factor, for depth of field and total light
Crop factor changes the framing, not the lens. A 50 mm lens is always a 50 mm lens; it just sees a smaller rectangle.
Equivalent aperture matters for depth of field and total light gathered, not for exposure. An f/2.8 lens meters as f/2.8 on any format.
The circle of confusion is a judgement about acceptable sharpness at a viewing size, not a physical constant.
Equivalent focal lengths on 645 film
| Lens | Full-frame equivalent |
|---|---|
| 12 mm | 7.4 mm |
| 16 mm | 9.9 mm |
| 24 mm | 14.9 mm |
| 35 mm | 21.7 mm |
| 50 mm | 31.0 mm |
| 85 mm | 52.8 mm |
| 135 mm | 83.8 mm |
| 200 mm | 124.1 mm |
Frequently asked
What is the crop factor of a 645 film sensor?
0.621, calculated from its 69.70 mm diagonal against full frame at 43.27 mm.
Does a crop sensor make a lens longer?
No. The lens projects the same image; the smaller sensor simply records a smaller part of it, which looks like a longer lens.