How do you calculate the viewing distance that matches a photo’s original angle of view?
Asked 11/30/2012
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If a photo is viewed from the right distance, it should subtend the same angle of view as the lens used to make it. How can you calculate that viewing distance for a print or display of diagonal size d, given a lens focal length f (using 35mm-equivalent if appropriate)?
For example, what viewing distance would match a 12×8 inch print made with a 24mm lens? Also, does this have anything to do with the common claim that a 50mm lens looks like human vision?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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The formula you're asking for is
x = (fl * d) / s
Where s is the diagonal size of the image sensor — 43.3mm for a full frame sensor.
However, for a 12" x 8" landscape print from a 24mm lens, your viewing distance works out to be about 8 inches — not exactly comfortable — and that's if your eyes can actually focus properly.
A picture being flat means its perspective remains the same whatever your viewing distance, so I wouldn't worry about trying to match up the field of view. The whole thing about 50mm lenses giving the same perspective as the human eye just means the view through the viewfinder is not enlarged, or shrunk, and that if you open your left eye the view you get is pretty much the same. The eye actually has a much wider field of view than a 50mm lens.
There is something to be said of moving images which fill your eye's entire angle of view, giving you an enhanced sensation of movement. This is the principle IMAX cinemas are based on. For still images you don't get the same effect.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
0
Generated from our catalog & community — verify before relying on it.
To match the photo’s original diagonal angle of view, use:
x = (f × d) / s
where:
- x = viewing distance
- f = focal length
- d = image diagonal
- s = sensor/film diagonal
For full frame / 35mm-equivalent, s = 43.3mm.
So if you use 35mm-equivalent focal length, the formula becomes:
x = (f × d) / 43.3mm
Example: a 12×8 inch print has a diagonal of about 14.4 inches. With a 24mm lens:
x ≈ 24 × 14.4 / 43.3 ≈ 8 inches
That’s quite close, and not always a comfortable viewing distance.
Two important caveats:
- Perspective in the photo is set by camera position, not by focal length. Viewing distance changes how large the image appears, not the perspective recorded in it.
- The “50mm equals human vision” claim is oversimplified. It does not mean human vision literally matches a 50mm lens in all respects, nor does it depend on a specific print size. It mostly refers to a view that appears neither strongly wide-angle nor telephoto, and on some cameras/viewfinders it looks roughly similar in magnification.
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