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I consider a "normal", comfortable working distance (when photographing people) to be about 6 ft (180 cm). But then it occurred to me that there might be a technical definition for a "normal" distance because there's a technical definition for a "normal" lens, where the focal length approximately the length of the diagonal of the frame.

Is there a technical definition for "normal" working distances at which to photograph subjects?

xiota
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  • It would depend on the "subject". Assuming there were such a thing, the "normal working distance" is very different between macro, portrait, street, landscape, astro and any other genre of photography you can think of... – twalberg Jan 29 '19 at 18:27

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I don't think this is a commonly-agreed upon or standard term. The phrase "normal distance" does not appear in the Focal Encyclopedia of Photography, and Google searches for 'photography "normal distance"' do not show any real pattern of use. (Most references are either as opposed to macro distance or actually referring to normal viewing distance for prints or screens.)

Because perspective is solely determined by distance between camera and subject, there's at least a common-sense answer to this: a normal distance is the same distance one might stand from that subject to observe or interact with it in real life. For people, it can range from a conversational distance to, maybe, across the room. Closer than that looks odd, as does an ultra-telephoto perspective. The same can apply to buildings, bugs, cars, or whatever else you're photographing.

mattdm
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  • I found some optometry references for "normal working distance" that seems to depend on specific circumstances. Apparently one definition has to do with the distance at which there is no physiologic accommodation response, which is desirable when looking through a patients' pupils to examine their retinas. – xiota Jan 30 '19 at 01:29
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Regardless of focal length, portrait perspective is determined only by the distance at which the camera stands, which is important. This could include like not making the nose appear larger than it is. Focal length does of course influence where you need to stand.

It is all opinions, but 6 feet might be considered a minimum. 5 feet can be too close for portraits, and 4 feet absolutely is. Many studios prefer 8 or more feet for formal portraits that they hope to sell. The 105 mm lens was popular for 35 mm film portraits solely because it forced standing back properly. Some preferred a 135 mm lens for same reason (speaking full frame, cropped sensors would use shorter lenses to stand back at same distance).

Focal length and subject distance can vary, depending if it is a head and shoulders shot, or full length or group. But in every case, there is this same minimum distance for proper portrait perspective. Zoom in all you want, but do stand back a bit.

Some users imagine a 50 mm f/1.8 lens is needed for outdoor portraits, thinking to blur the background. The pros would avoid the f/1.8 issues, and would likely use a 200 mm lens to blur the background even better, plus better portrait perspective too.

WayneF
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  • What do you mean by "f/1.8 issues"? A longer lens that has the same amount of background blur, subjectively speaking, would have a similar (shallow) depth of field as the 50mm f/1.8. Do you mean that f/1.8 is too bright for outdoor conditions? I have rarely had a problem with that. – thirtythreeforty Jan 29 '19 at 20:03
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    I mean f/1.8 has typical optical aberrations which hurt sharpness, particularly in the corners ... the typical problems which are very undesirable for astronomy too. No, if a reasonably distant background (like 30 or 40 feet), which is very possible outdoors, the longer lens must stand back from subject, but then can easily show much greater blurring of backgrounds than the 50 mm at f/1.8, yet greater depth of field at the subject (even at like f/4, better optical quality). 50 mm is too short for portrait perspective anyway. See my site at http://www.scantips.com/lights/dof.html – WayneF Jan 29 '19 at 22:27
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It relates to binocular vision and stereopsis. Stereopsis is where two distinctly different images exist on the L/R retinas due to angular differences; which the brain then combines as a single image with binocular depth information (as opposed to monocular cues). The brain does some amazing things in this situation in order to create a "normal image" perception.

This varies both by individual and situation (i.e. the distance between near/far objects). But the significant majority of it occurs at less that 10ft... beyond 10ft monocular (2D) cues are much more significant (some say beyond 3-5ft).

So the "normal distance" (perspective) is that where normal monocular/2D vision/cues align with the resulting 2D image... most commonly accepted to be around 10ft when photographing facial features IME.

Steven Kersting
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    Do you have a reference for further reading? – xiota Jan 30 '19 at 22:09
  • Nothing that puts it all together in terms of photography... but there is plenty on stereopsis and binocular/monocular vision (depth perception) available. I was once taught/told that the mind puts people at a distance of about 12ft regardless of their distance (if you know what they look like). I.e. your significant other never looks "odd" or distorted by perspective; and I've found that to be true. But you can turn that off if you want... next time you kiss someone pay attention to how huge their nose looks from that distance! But your brain can't "fix" the perspective in a 2D image... – Steven Kersting Jan 31 '19 at 17:38
  • Nothing says "I love you" quite like "What a big nose you have." – xiota Jan 31 '19 at 20:24
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The premise of your question is flawed in that a normal lens isn't really a technical concept. A normal lens having a focal length approximately equal to the diagonal of the film or sensor is just an observation, not a definition. A normal lens is considered normal because it fills the frame with common subjects at comfortable working distances and natural perspectives. What we consider a comfortable working distance or natural perspective is a function of the distances at which we normally observe things in our everyday experience.

StackOverthrow
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  • The OP is asking about normal distance not normal lens. – Mike Sowsun Jan 29 '19 at 17:38
  • @MikeSowsun And I'm explaining how the two are related. – StackOverthrow Jan 29 '19 at 18:02
  • "Normal lens" is a commonly used term with a generally uniform meaning in photographic communities. It is a technical concept in the sense that it describes a relationship between two measurable things. – Michael C Jan 29 '19 at 21:18
  • @MichaelC That relationship is a coincidence. It's just a rule of thumb that has no real technical significance. – StackOverthrow Jan 29 '19 at 22:10
  • @MichaelC None of that has anything to do with what makes the lens "normal" to the photographer. – StackOverthrow Jan 29 '19 at 22:17
  • @MichaelC Neither the focal length nor the angle of view directly affects perspective. Angle of view affects the working distance at which common subjects fill the frame. Working distance is what affects perspective. A "normal" working distance, and therefore a "normal" lens, is defined by our familiar visual experiences. Thinking that a "normal" lens is defined by some technical characteristic is reasoning completely backward. We can measure and describe some technical characteristics of a normal lens, but they are not what make it normal. – StackOverthrow Jan 29 '19 at 22:46
  • @MichaelC You're reasoning backward. What makes a particular combination of focal length and media size "normal" is the angle of the central visual area of the human eye, the sizes of objects we look at, and the distances from which we look at them. – StackOverthrow Jan 29 '19 at 23:31
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    A normal lens will register ~ 45* circular FOV on the sensor/film (measured as diagonal), which correlates directly to the "normal viewing distance" of a print. An 8x10 viewed from 12" (the image diagonal) will occupy ~ 45* FOV. I.e. the FOV recorded is normal for the FOV occupied by the displayed image.

    This "normal distance" also affects many other commonly accepted image aspects (CoC, DOF, sharpness, etc).

    I do believe this correlation was probably found in reverse by first observing "comfortable/normal" viewing distance/behavior.

     – Steven Kersting Jan 30 '19 at 21:53