bpulv Loc: Buena Park, CA

Everyone should be aware that the Wikipedia article has an accompanying warning that the article is currently lacking all the necessary citations that Wikipedia requires before Wikipedia considers the article to be accurate. That does not mean that the author is not correct. It only means that the article does not have the highest level of confirmed accuracy required.

therwol Loc: USA

I'm old enough to remember that computers were used extensively by the late 60s in business and manufacturing design, not to mention by the government. We couldn't have made quick and accurate course corrections necessary when we were blasting people into space in the 60s without the use of computers. Students used slide rules for homework but were beginning to learn how to program computers to do it. As for manufacturing tolerances, you are right. The equipment we use today in manufacturing didn't exist back then.

mcveed Loc: Kelowna, British Columbia (between trips)

Good grief!! The focal length of the human eye has absolutely nothing to do with it. 50mm was chosen because the it has the same field of view as the "average" human eye. You can check for yourself: put a 35-70mm zoom lens on your camera, select a circular target or something with a distinct shape, look through the viewfinder keeping the other eye open. Focus on the target. Now adjust the zoom of the lens until the target in the viewfinder is the same size as the target seen with your other eye. Now look at the focal length scale on your lens. End of argument. You can play with this by zooming in and out: as you zoom in the target in your viewfinder will become larger than the one seen with the other eye - zoom out and it becomes smaller.

blackest Loc: Ireland

I think you have to look at registration distance which is with dslrs around 46mm. Non dslr's such as range finders are free to have a shorter registration distance. Another thing to consider was the double duty lenses have performed in the past being used both for taking photo's and enlarging them. That might be a red herring as to why 50mm but the construction of enlarging lenses are relatively simple.

Now having played around adapting enlarger lenses for dslr use. For infinity focus they essentially sit at their focal length (50mm). to focus nearer they have to move forward to focus a 50mm at 500mm (about a foot and a half) needs a forward move of around 5mm (55mm). with m42 lenses the registration distance is around 45.6mm you need to get a helicoid and perhaps more importantly an aperture behind the lens. The gap between the registration distance and a 50mm lens is about enough to do that.

If you go shorter than 50mm it gets complicated you cant hold a 35mm lens 35mm from the film plane if there is a mirror in the way.

So the simplest lens design and shortest would be the 50mm, close enough to be a 'normal' view and maybe one of the cheapest to manufacture.

Maybe 50mm isn't the 'normal lens" as we tend to think of it optically but the "usual" or "normal" lens to sell with a camera body...

So do you want the normal lens or something on special order?

Painter Ralph

My understanding is that it is based on how a full frame looks in a standard 8x10 Print viewed at some average distance. Nothing to back this up. Just what I was told at my first camera club 40 years or so ago.

bcrawf

kymarto Loc: Portland OR and Milan Italy

Registration distance has to do with mirror clearance. As I keep saying, it has to do with image circle. A normal optical design has an image circle pretty close in diameter to the focal length. Wide angle lenses need a special design to make a larger image circle than the focal length, as you point out.

Actually moderate tele lenses can be even cheaper than a 50, because the image circle is large enough to use only the sharp center of the image circle. Many of the earlier moderate teles were Cooke triplets, with only three elements, much simpler to make than a 50. But teles have a foreshortening effect.

The easiest shorter lenses to design to cover the frame diagonal are those only slightly longer than that diagonal, avoiding having to use the very edge of the image circle. The fact of registration distance fits with the constraints of the frame size and not vice-versa.

blackest Loc: Ireland

I’m not sure about that. Isn’t the image circle more a function of the lens’s diameter? E.g a canon ef-s 50mm is a 50mm lens but the image circle doesn’t cover the 35mm frame. If you adapted a medium format lens to dslr the image circle would be much larger...

For longer lenses an f1.4 50mm needs an entrance pupil of around 25mm for 100mm it would be 50mm diameter. Wouldn't such an optic be more expensive to produce? Perhaps less general purpose too.

Shel B

While a 50mm lens, on 35mm film, certainly doesn't give a wide field of view like the eye sees, the 50mm lens sees about what we call "normal" perspective....no really noticeable foreshortening or exaggerated wide angle effect. It's.....normal. My humble opinion.

Billynikon Loc: Atlanta

Rather matters whether one is shooting DX or FX. It is a rather long lens in DX but perfect for general use as an FX lens.

pendennis

For the most part, longer focal length lenses are slower (e.g. f2.8), so the entrance pupil doesn't have to be proportionately larger.

pendennis

I'm referring to the pre-computer era (ca. 1920's), when the "standards" first came into existence. Those numbers came into being based on charts developed by optical engineers.

I used a slide rule well into the 1970's for business analysis, even after I bought my first Texas Instruments electronic calculator. Computers were in more widespread use, but shared time was far more expensive than today's costs.

The calculations for the space program were largely done by hand. Here's a link describing just how some of these were accomplished.

https://www.npr.org/2016/09/25/495179824/hidden-figures-how-black-women-did-the-math-that-put-men-on-the-moon

mcveed Loc: Kelowna, British Columbia (between trips)

Nonsense. You are trying to invent answers. Read my previous post for the obvious and correct answer.

therwol Loc: USA

I guess this is off topic, but yes, I've read about women in this article. By the time of the moon shot, NASA was running simulations of various aspects of the mission on an IBM 360-75 in Houston, and both the Saturn rocket and lunar lander had computers to analyze telemetry. It was a time of incredible transition in technology that had its seeds in WWII and the 50s.

Once I bought a programmable TI calculator in the 70s, I put aside my slide rule. My crowning achievement was programming the thing to play blackjack with an actual 52 card deck.

Oh, and the other reason lenses got better after about the 70s, ED glass and aspherical elements already mentioned.

OldBobD Loc: Ohio

I think I read somewhere that the early SLRs (Contax?) required more room for the mirror to swing than a 43mm lens would provide.