Good question. It depends on the size of the film/sensor. With 35mm, say, a 300mm would definitely be a telephoto but with large format cameras it's just a 'standard' lens.
The usual formula, as far as I'm aware, is to take the diagonal measurement of the film-frame and this will give you the focal length of the standard lens to get a 'natural' view.
With 35mm the frame is about 43.5mm so that would be the standard lens - I think the main reason that 50mm became the normal lens was that when Leica produced the first 35mm camera they had a 50mm design from another format (cine?) available, so didn't bother re-designing one just a few millimetres away. Other makers then just followed suit.
Any mathemeticians will be able to work out what the magnification is by dividing 300 by 43.5. And working out the diagonal of any other formats, such as the D50's is just a matter of finding the square route of the sum of the squares of the two quoted dimensions of the format size - easy isn't it!!
OK, it's a long time since I was at school but at least I can remember the formula even if I can't work it out!
Last edited by Adey Baker; 01-02-06 at 07:51.
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