Focal Lengths

[Paul_O]

I've been meaning to ask this for a while and after reading about the difference between screws and bolts and sucking and blowing, this probably won't sound so silly now ;)

Anyway, how did the major focal lengths come about ie 35mm, 50mm, 85mm, 135mm, 180mm, 200 and so forth? I've noticed that zooms usually have unconventional lengths such as 17-40, 70-200 and 100-400 but the "old style" measurements are still marked on the barrels are they not?

Any enlightenment would be much appreciated

Paul

[FlipsidE]

I think 50mm came around becuase it approximates what you see with your eye.

FlipsidE

[Paul_O]

That's what I've read too but I think that there's some conjecture whether it's 35mm or 50mm?!? Anyway, so that's 2 lengths out of the way ! :)

Paul

[cactusclay]

It all started 647 years ago, when a fisherman discovered a glass float and it's all history from there.

[PhotosGuy]

I think 50mm came around becuase it approximates what you see with your eye.
I've heard that too, but 35mm is closer. If no sensor crop factor, I used to do this for film:
105mm: hold your arm out with the thumb & fingers spread = angle of coverage.
50mm: both arms out with thumbs touching.
35mm = 3 hands.
Not as good a "show" as a directors loupe, but it impressed gullible clients! ;-)