[Leica] How did 50mm become the "normal" lens for 35mm cameras?

[Howard L Ritter Jr]

I’m not sure I understand what you mean, Bill. This looks like circular reasoning: no magnification or reduction with respect to what standard? Only itself. 

The size of the image on the film has no inherent relationship to the subject itself unless it’s taken with a macro lens at 1:1 reproduction ratio. Anything else is an arbitrary representation that depends on the focal length and distance to subject. Pick a print size and a viewing distance. Choose the FL to be that which gives the same image scale on the print as the scene that you’re viewing from the same point as the camera. Maybe for one person that’s 50 mm, maybe different from others. The process would be totally arbitrary.

Is it that 50 mm gives a unity-magnification view in the viewfinder of a FF SLR? That’s dependent on the apparent size of the focusing screen produced by the FL of the VF eyepiece. Again, arbitrary. Designers could make the image formed by a 35-mm lens on the screen appear at unity magnification by using a wider-field eyepiece on the VF.

Any focal length for any film frame size is totally arbitrary. The human eye takes in nearly 180 degrees, so one “no magnification or reduction” standard would be a fisheye lens. OTOH, the field of foveal vision, full resolution, is a fraction of a degree, so another standard would be a 1000-mm lens. 

I’ve heard it said that the field of attention of the human eye-brain system, the principal stuff that we apprehend when we look at a scene, is about the same as that captured by a lens whose FL is about the same as the diagonal of the film frame. So a FL in the range of 40-50 mm would fit that bill. That’s also full of assumptions and arbitrary decisions. The 50-mm decision is probably rooted in many things, including what’s in this paragraph and what was available when 35 mm photography was evolving.

Simple P&S cameras had 35-mm lenses when they were FF film cameras and that seemed to make most users happy. Today the few fixed-lens FF digital cameras, I suppose the only two, in fact, use 28 and 35 mm, respectively: the Leica Q and the Sony RX1. 

I use 35 mm as the default lens on my 240 and MM when I head out. I don’t even own a modern 50-mm lens.

The bottom line is: Normal FL is what the photographer regards as such. But it doesn’t have to do with a zero point between magnification and reduction.

—howard


> On Sep 16, 2016, at 6:17 PM, Bill Clough <billclough042541 at gmail.com> wrote:
> 
> It's called a normal lens because it neither magnifies or reduces the image.
> 
> --Bill Clough
> 
> On Fri, Sep 16, 2016 at 11:15 AM, Adam Bridge <abridge683 at fastmail.com>
> wrote:
> 
>> I’m just wondering if anyone knows since 43mm would be the more rigorous
>> focal length for tradition 35mm film.
>> 
>> Thanks!
>> 
>> Adam Bridge
>> 
>> 
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