# [q] natural point of view focal length

Discussion in 'Classic Manual Cameras' started by vlad_p, Jun 13, 2009.

What focal length is most closely represents what a human sees for 35mm film.
(50mm is way too narrow in my opinion).
And a second queston (perhaps should have been a separate one).
am I correct to assume that to achive
'most natural' -- "as I saw them" pictures --
I should use
a) no flash
b) a natural view lens (probably the answer will be somewhere between 24 and 45mm) ... but I am not sure
c) horizontal plane
d) eye level
e) perhaps low ISO film
or is there a different 'formula' for achieving "what I saw" on a photograph
I am somewhat confused by the fact that I can never capture things the way
I saw them. May be I am incorrectly assuming that my eyes are 'fixed focal lenght' (I know they are not... but not sure how to 'express' that)
thank you

2. ### joe_c|5

The focal length to avoid perspective distortion depends on the viewing angle of the final photograph. One rule of thumb is that people tend to look at photographs from about the same distance away as the diagonal of the photograph. Following that guideline, a 43.3mm lens would look the most natural on a 35mm camera.
If the photographs are viewed from closer than the length of the diagonal, a shorter focal length lens would be needed. If the photographs are viewed from farther away (particularly true of small prints), then a longer focal length would look more natural.

3. ### janne_moren

A "natural" focal length - there really isn't one. It depends completely on how the viewer views the picture. Think of it this way: the image is "natural" when the scene falls onto our eyes the same way the real scene would have done had we been there. That means, essentially, that the image is "natural" when the edges of the image as seen correspond to the edges of the image as shot. So, if you shoot with a lens with a 45 degree angle of view (around 42-45mm focal length for most 35mm systems), and then place the image so that the angle of view, edge to edge, is also 45 degrees, then that would be a "natural" image.
This means that any focal length can be "natural", if you just place the print or screen appropriately. Different focal lengths after all just cut out a narrower or wider view of the same scene. So you could in principle shoot with a 200mm lens, then place a small print a fair couple of meters away and it'll look natural - albeit rather small. Or you could shoot with an 15mm lens and place a big print right up against the face of the viewer (or shoor a 180 degree fisheye and print into the inside of a half globe) and it'll look natural.
In practice, we humans tend to want to see images so that they fill as much of our vision as possible without us having to move our heads around to take it all in. That tends to translate into approximately 40-45 degrees or so. Which is close to the "normal lens is equal to the diagonal of the film plane" rule of thumb. You can make a good argument for anything from 35mm to 55mm focal length (in 35mm terms). There's no more exact answer since each viewer and each viewing condition is different.
As for the other points, no, generally there is no rule of thumb to make "natural" images in the sense that they represent what you saw. Problem is that a camera and film reacts very differently to light than our (low quality, highly adaptive, heavily postprocessing) eyes do. Fill flash, for instance, may be needed to capture both deep shadows and sunny highlights that we have no problem perceiving clearly when we're at the scene. And our eyes are also very noisy and low resolution in low light, so there a high-ISO film would probably be more correct (probably BW film, subsequently toned blue).

4. ### subbarayan_prasanna

There are also other variations between a natural eye vision/perception and a camera's cyclops type perception.
1. the normal vision with both eyes can cover as much as 180 degrees for some people, with each eye covering 90 degrees horizontally.
2. in the vertical the human eye is comfortable more below the horizon line from the eye [down to 45 degrees from eye level], where as it is not comfortable beyond 20 degrees or so above the horizontal. We use this parameter to adjust the seating angles in movie houses, to get the screen within the comfort zone.
3. the perspective produced by the camera lens of 24mm is a lot more angular than that perceived by the eyes. [Though the human eye is capable of such acute perspectives when needed.] The brain intervenes and interprets the perspective seen by the eyes as they focus on different points/ areas of the scene. [In other words the eye sees a multi-point perspective in several planes and the brain interprets it into a composite.]
The camera arrests all these variables into one cross section with a single point perspective. Thus it is difficult to fix the "most natural" focal length or perspective. Such will also vary from person to person and the viewing preference.
This is why the approach to developing [choosing] the perspective in art work [sketching, painting, etc.,] differs so much from that in photography.
if you are more depply interested in the subject, you may want to look at the following books.
Ludvig von Bertelanffy, Perspective systems in art , [paperback] 1970s??? [There is one chapter comparing Western and Japanese art forms, germane to your query.]
Rudolf Arnheim, Art & Visual Perception , psychology of the creative eye, [Paperback]UC Press, Berkely & LA, 1965.
You may find these in old book shops or in Libraries. Regards, sp.

5. ### Rob_the_waste

In using my Zenit 3 with a Helios 44 lens, you can look with both eyes open and see the same thing in virtually the same scale.

6. ### cliffmanley

And for the ultimate, from two points divided by about 2 1/2 inches to have a 3 dimensional view, with depth and reality, just like you see it with both eyes. 3D stereo is really the only way to truly capture what you see, unless you are blind in one eye. of course. For truly natural looking stereo, the photos should be taken with the same focal length as the stereo viewer lenses.

7. ### bueh

What focal length is most closely represents what a human sees for 35mm film.​
The human visual perception system is very different from how a camera sees things. But since you want simple, clean numbers.... (all focal lengths 35mm format equivalent): the angle-of-view is about 15-17mm, the apparent perspective is like a 40-45mm lens, but the center of attention (what we really see) is more like a 200mm or 300mm lens.
am I correct to assume that to achive
'most natural' -- "as I saw them" pictures --
I should use
a) no flash, b) a natural view lens (probably the answer will be somewhere between 24 and 45mm) ... but I am not sure, c) horizontal plane, d) eye level, e) perhaps low ISO film​
No. The human visual perception system is very differently from a camera/lens/film system. The human eye is a very poor one-element lens with lots of spherical and other optical abberations, but most of these "errors" get smoothed over in "post-processing". If you really want to emulate human perception, use a 3D video camera (if there is such a thing), but you will never be able to reconcile the three phenomenons I noted above (field-of-view vs. rendering of spatial relations vs. center of attention). Welcome to world of photography!

8. ### charles_stobbs|3

I think my seeing (identifying) potential photo subjects has changed. For years I used a camera with a 50mm lens and subconsciously looked for views that would best fit that format. Now I use 35 to 45mm lenses more and I think my perception of a good subject have changed.

9. ### richard_oleson

There are some really excellent responses here - this should be archived for the thousands of times that the "same angle that the eye sees" question comes up.

10. ### robin_terrey

In a Modern Photography article from the 1970's a German was wondering why 50mm was a normal lens. He had taken a shot of a bridge and church in a German town. He was unhappy with the print. Visiting a family in this town he noticed an engraving of the same view. This led him to use various focal lengths, He came to the conclusion that a focal length around 105mm gave the same representation as the artist eye saw it. Later he refined that down to focal length of 90mm. He wrote to Leitz and asked why O. Barnack had chosen 50mm as the normal lens. Leitz sent him some photocopies of articles from 1930's Photographic magazines, the gist was that the human eye needed so many points to reconise something and so Barnack calculated what focal length would give the required number of points and came up with 51.?mm which was rounded to 50mm.
Going back to the artists view, it would seem that our eyes zoom in on the main point and to our view enlarge it. Then when we get our print we are unhappy with the results because they are not as we remember it.

11. ### JDMvW

That the human eye works as well as it does is a miracle, but one of software/wetware processing rather than the miracle of good engineering of the optics proper. Bueh and the others are right.
The 50mm focal length for 35mm sized film/sensor is an historical tradition, rather than a strictly scientifically arrived at number. As already noted, the variable of viewing distance from the "print" has to be considered also. As frequently pointed out in books about this sort of thing, if you view a wide-angle print from a very close distance, the "distortion" of the wide-angle lens goes away.
Seeing the same thing through the viewfinder as with the other eye, depends more on the nature of the viewfinder rather than the focal length of the lens, strictly speaking.

12. ### richard_oleson

I'm sure it had NOTHING to do with the fact that Tessar and Cooke Triplet lenses (the simplest formulas for an anastigmat lens of useful speed) had a good coverage angle of about 45-50 degrees.

13. ### cliffmanley

"Perfect photographic record. In the stereo photograph we have the perfect, i.e.complete representation of the object photographed, as it appeared to the eyes when the record was made. No other photographic method can give the marvelous illusion of reality, the depth, roundness, relief, and perspective effects which constitute the outstanding features of the stereo photograph. Not every scene makes a good ordinary (single lens) picture. In many cases the photographer views a scene that in color, lighting, perspective, and mass, combined is pictorial effective, But when reduced to a one-plane ordinary print, much of the effectiveness and perspective have disappeared, Any scene that is effective to the eye, will however, make an acceptable stereoview, an exact reproduction of the subject--as the eyes saw it when the record was made. "
F.C. Tilney, Surrey England 1923

14. ### robin_terrey

The article I refered to in the earlier post was in the April 1974, Modern Photography. Horst Staubach was the photographer who wondered, "Just how normal is a normal lens?" He discussed with Dr. Sauer of Carl Zeiss about his findings. He confirmed them by saying that a focal length 70 to 80% longer than normal focal length does result in a more natural looking photograph. The only question left is what is a normal lens. Staubach continues, "Why was it generally accepted by the photographic world (long before 35mm cameras came on the market) that the normal focal length of a lens should approximately correspond to the length of the diagonal of the picture format?" He concluded that this focal length would insure a 'natural perspective,' and this had something to do with the normal viewing distance which is about 250mm (approx. 10"). He final point was the authorities were wrong because perspective does not depend on focal length of a lens. So in conclusion, a normal lens is what YOU decide is the normal lens for YOUR style of photography!

thank you for all the answers sofar.
I understand now that it is the 'stereo' and exposure adjustment that the eyes make that is impossible to replicate with one lens and a flash (or sunlight) (or may be there are some digital/scanning tricks that exist... I will read more on those)
the focal length of the lens turns out to be much less important.
thank you again,