50mm "Normal" Lens... Ok, but "Normal" on FF or APS-C Sensor?

Started Nov 10, 2012 | Discussions thread
Joseph S Wisniewski
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It all depends on how you view the final image...
In reply to REShultz, Nov 11, 2012

REShultz wrote:

It is frequently said that the 50mm is a normal field of view. Does this come from a FF perspective or a crop sensor?

Many define a "normal" as a lens with a focal length equal to the image diagonal. That's not quite right, but it's a pretty good definition. In that case, the "normal" is..

  • 43.3mm for FF
  • 28mm for Nikon, Pentax, and Sony crop cameras
  • 27mm for Canon crop cameras
  • 21mm for four thirds

But that doesn't tell the whole story. In fact, our huge range of modern viewing technology (10 inch iPads, 24-30 inch desktop monitors, cheap 22 inch tabloid publications, 13-17 inch notebooks, 60 inch LCD TVs, 3 inch Polaroids, 22 inch "super B" printers, etc. etc. etc) has just blown it to smithereens. Why?

That definition of "normal" is based on the idea of a "transparent print". When you look at the print, the subjects have the same perspective, relative to the eye, as they did in the original scene. This has nothing to do with the "field of view" of the eye. The eye, or more properly, the human visual system (eye, brain, muscles that let the eye scan, even neck, back, and eyebrows) has a variable field of view, from roughly 240 degrees during full scanning, to 6 degrees during a flight-or-fight fixation. So, if it's not FOV, we circle back to perspective.

A human looks at another human. At 6 feet away, a 6 foot tall human is 53 degrees to our vision. That signals certain things about danger (especially if it's our same gender and not of our "clan") protection (especially offspring of our clan, or a member of the opposite gender) mating practices, etc. Move that person 25 feet away, and they're only 14 "degrees tall".

So, when we're looking at a print and the subject is 14 degrees tall, we get that "safe distance" for a possible threat or "too far" distance for our offspring reaction. If the picture itself was taken from that same distance, the print carries the same emotional impact as what the photographer saw. It was "normal".

For common 1900-1995 technology, that involved holding an 8x10 print at 12.8 inches (32.4cm) from your eyes. Which sounds like a really strange thing to do, until you realize that, at one point, the 8x10 print (12.8 inch diagonal) was the most common way of viewing a commercial print, and 12.8 inches is also approximately the distance from the eyes to the print when you hold if the most common way, upper arms down, elbows at 90 degrees.

Now, it's just pure coincidence that these two 12.8 inch dimensions coincide. It's not physics, magic, or destiny. 8x10 prints are common because it's a good "portable" and economical size for books, printing, cutting glass plates, etc. 12.8 inches is within the "accommodation" distance of human vision and the length and joint designs of human arms.

Right now, I am viewing "abnormally". I am using a 30 inch diagonal monitor, 24 inches away from my eyes. The "focal length", in the truest sense of my eyes focusing, is 24mm, and the diagonal, obviously, 30 inches. The ratio of focal length to diagonal is 0.8, and any shots taken with that same ratio (a 35mm lens on a 43.3mm diagonal FF camera, or a 22mm lens on APS crop) look natural, while ones taken with the conventional 50mm normal on FF look "too close" and create more "tension" or "stress". This can be useful for creating "dramatic tension" if the photographer is aware of it, and masters it. It will also make viewing the images more aggravating and stressful if the photographer is unaware of it, and lets it master him.

All in all, the thing to keep in mind is that in 2012, for the most part, images are viewed bigger and/or closer than they were in 1900, so plan accordingly, and shorten your "normal" a bit. 0.9 of the diagonal is probably about right, a 40mm on FF, a 25mm on APS, and ignore the camera manufacturers shoving 50mm on FF and 35mm on APS down our throats, because that's what's easy for them to make, but not easy, as photographers or viewers of photographs, to deal with.

wizfaq normal

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Rahon Klavanian 1912-2008. Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed. Ciao! Joseph www.swissarmyfork.com

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