What is a 'normal' lens?

On 35mm a 'normal' lens seems to be 50mm. I heard the term 'normal' lens often, but what does it mean? Sure, 50mm is a nice medium zoom level, but is there some more technical criteria for 'normal'? I know the focal length of a lens affects perspective as well as angle-of-view so maybe that has something to do with it?

It's typically about 50-55 degrees angle-of-view. So with 6x4.5 film, it's more like 75mm

The rule of thumb is take the diagonal of the film and that's about the focal length for a typical normal lens.

"normal" is close to your eyes perspective. For example, put your eye to the camera finder, and then take your eye away. The images should look roughly the same size.

For example, put your eye to the camera finder, and then take your eye away.

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Wouldn't that depend on the viewfinder though?

No. Say, it is a person, that persons head will look similar in size while viewing it though the viewfinder, and when you take your eye off.
When you look though a wide lens, and then look with your eye, the person will look a lot smaller compared to your eye.

You lens alone will not change perspective. One thing truly affects perspective: your location relative to what you are shooting. That is what perspective means, after all. If you put a camera on a tripod and take the same picture with many different lenses, without moving the camera between shots, the perspective does not change. The angle of view changes.

Using different lenses from the same point simply to obtain the desired angle of view will not change perspective. However, changing focal lengths quite often causes a change in location of the camera, so it is often stated that lenses themselves change perspective. Try zooming in and walking backward simultaneously (or vice versa) at a rate that keeps a foreground subject the same size throughout. Then try just standing in one place and zooming in and out. Big difference between the two!

To me, a normal lens is the lens that you use when you want to shoot from the standard eyeball viewing distance from something without heavily distorting the relative locations of objects within the frame. That means that if I put the camera up to one eye, the sizes and locations of objects look the same as I see them with my other eye.

I think my 55mm works as a slightly more "true" normal lens than my 50mm. I find myself often having to move slightly closer with a 50 to get the shot that originally caught my eye before raising the camera, since everything shrinks a bit when I raise the 50 to my eye. I think a 58mm would be even slightly more close than my 55. The 55 shrinks things just a teeny bit; almost not noticeable.

I love normal lenses for their ease and quickness of composition. You see something, you raise the camera, and you pretty much already have the composition.

Markok765 said:

"normal" is close to your eyes perspective. For example, put your eye to the camera finder, and then take your eye away. The images should look roughly the same size.

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That's strange most peoples eyes have the same perspective as any lens from wide angle to telephoto at any given viewpoint

Perspective is to do with image subject distance not specifically focal length. Stick your camera on a tripod take some images from the same position with a 17mm, 28mm, 50mm 135mm etc, enlarge them so that a common feature is the same size in every print and you'll see that the perspectives are all idenical, but the field of view differs.

Then using the same lenses alter the camera object distance to keep that common feature the same size on the negative then you'll see the perspective change radically.

Ian

A "normal lens" is a lens with a focal length equal to the diagonal of the film (or other recording media).

It has nothing to do with the view through the viewfinder, since that is influenced by the optics in the viewfinder.

For a 35mm camera, the "normal lens" should really be 43mm, but 50mm is commonly used instead.

"The `normal' focal length is equal to the diagonal (or diameter .. or ..) of the film frame". In 35mm, that works out to ... 47mm (ellipsis there because I have not verified).
I've dug through the origin of this, and it it appears to have originated arbitrarily among the photographic community in the mists of time.
Having been involved in lens design and manufacturing, I've found that lenses that conform to that normality seem to be easiest to design (largest apertures, correction from errors and aberrations) and most economical to produce.

Anyone who has attempted portraiture using a wide-angle lens will be familiar with the "ballooning effect", inversely connected to the lens' focal length. I (and others) consider that effect to be excessive with a "normal" lens.
At 90mm in 35mm, and 150mm in 120, that ballooning effect is minimal and faces appear as they do to the naked eye - accounting for the widespread use of these lenses in portraiture.

The normal focal length is definitely historically linked to the diagonal of the film negative size. 50mm has become the number for 35mm. For MF 6x6 it would be 85mm (but they have settled on 80mm) and interstingly if you go 6x4.5 you get 75mm...which is the standard normal lens for that format. Why the slight differences...don't know. Someone with better lens knowledge may be able to explain why a lens with a focal length the same as the diagonal gives the most realistic (least distortion/flattening) compared to the other focal lengths..K

The focal length of our eyes is 42mm. Some compact cameras had this length instead of the 50mm. So Normal focal should be 42mm
A standard lens, is one around the 50mm length. It's called standard just because everyone included the 50mm lenses as kit.
Then, people mixed all this. So now, Normal and standard are almost the same concept.

without being all technical about the diagonal of the film,
or "seeing like your eyes" .. one could also say whichever
lens you use the most, be it a long or short lens, could be said to be
"your normal lens" when i shoot architecture, my 90mm ( on a 4x5 ) is MY normal ..
i am sure people who shoot vistas / landscape would say that their 210mm is THEIR normal.

YMMV

Prest_400 said:

The focal length of our eyes is 42mm.

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No, you're wrong. The focal length of our eyes is about 24mm, the size of an eyeball. You would look very strange with 42mm HUGE eyeballs!

Also the field of view of out eyes is both about 2 degrees and about 180 degrees at the same time - one for fine focus, the other for motion detection.

What that means is that any comparison with the human eye is irrelevant.

If the term "normal lens" is to have any meaning at all, it has to be "a lens with a focal length approximately equal to the diameter of the recording media".

If some individual photographers prefer a different focal length that does not make that focal length "normal", but "preferred".

It's either that, or the term is meaningless.

Another thing I've noticed is that 'normal' 50mm lenses on 35mm tend to be fastest. Wide-angle and tele are both slower usually. I'm not sure why this is, but maybe that's another reason these lengths became 'normal'.

OH NO!

Ole said:

No, you're wrong. The focal length of our eyes is about 24mm, the size of an eyeball. You would look very strange with 42mm HUGE eyeballs!

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OH NO. The focal lengt of eye is (maybe) 24mm. But it is something diferent. Normal focal lenght depends on circumscribed circle of film frame and is equal to diameter of this circle. (Eyeball has spherical shape of senzitized surface and works little bit different way.) This means that normal focus lenght is different for 24x36mm, for 6x7cm etc.
So for example:
24²+ 36² = 576 + 1296 = 1872
sqrt{1872} = cca 43mm

43mm is normal focal lengt for 35mm film.

petras@foto.sk said:

43mm is normal focal lengt for 35mm film.

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I agree wholeheartedly.

As I said,

If the term "normal lens" is to have any meaning at all, it has to be "a lens with a focal length approximately equal to the diameter of the recording media".

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