# Can someone share a history or origin of why 35mm FL was the "chosen one" in the first place?

Started Jul 25, 2013 | Discussions thread
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 Re: Normal focal length In reply to ProfHankD, Jul 26, 2013

ProfHankD wrote:

smallLebowski wrote:

I mean it's very versatile FL, but did they test it initially at the beginning era of photography and came to a conclusion that this FL suits best for starters or there was some other interesting story? Would like to hear that. Thank you.

P.S. I guess different brands had different perspective on best FL maybe?

As folks have said, 35mm is not the "chosen one" for anything.

There has been a little debate on this in this forum before, but "normal" focal length for 135-format (the real name of FF 35mm film) is the diagonal of the frame, which is sqrt(24^2+36^2), or about 43mm. However, it is easier to build fast lenses of a slightly longer focal length, especially for SLRs that have a mirror forcing the lens center to be farther than 43mm from the film plane. Recall that the focal length of a simple lens is the distance from the center of the lens to the focal plane at infinity. Thus, FF normals run anywhere from 45mm to 58mm.

The APS-C format is about 23.6x15.6, giving a 28mm diagonal. Of course, the roughly 1.5X crop would mean a 50mm equivalent would be 33mm -- pretty close to the 35mm focal length that was common for FF wide angles.

The perspective/view angle given by a normal lens is also considered to be a good match for how humans see the world, although that claim is harder to justify. It is true that viewfinder magnification is commonly set so that the view through the finder using a normal lens makes objects appear the same size as the view without the finder, which has the side effect of making it easier for photographers to work with both eyes open.

Yes. And the same calculation holds true for 2 1/4 film/camera where the normal focal length was regarded as 80mm. And it gave very much the same fov as around 50mm on 35mm cameras. (allowing for the square shape of the fov)

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Mike Fewster