What's measured when a camera is described as 35mm?

[itinerants]

Having been taking snaps for many years, I'm now developing an interest in photography proper. I've red several books and many magazines, but not one answers my question - what is actually measured when manufacturers refer to a 35 mm camera, or to sizes of lenses e.g. 35mm - 105mm? Even the most elementary tutorials assume that I should know this - but I don't. Can anyone explain - preferable in terms suitable for an idiot technophobe? Thanks.

[vehelpfulguy]

In terms of 35mm FILM size, this is the width of the frame from one side to the other, including the perforations.

This 35mm film is the same size as that used in most movies in the cinema.

In fact I think the sucess of 35mm film in still photography came about because of the availablity of 35mm stock used in movies.

You can read more about 35mm here

http://en.wikipedia.org/wiki/35_mm_film

[vehelpfulguy]

In lens terms the mm size refers to focal length, the distance from one end of the lens to the other.

The shorter the lens, say 28mm, the wider the area the camera can see but the further away it will look.

The longer the lens, say 80mm, the less it can see, but the closer up you look.

A lens which is 35mm-105mm is a zoom lens that can zoom back to 35mm to give you a wide picture, or zoom up to 105m to give you a narrow close up picture, or anything in between.

Note that the 35mm film size has NOTHING to do with the 35mm lens size, two totally different things.

More here

http://hypertextbook.com/facts/2002/MiriamJano ve.shtml

[vehelpfulguy]

Nice explanation here of lenses, with a simple diagram of different focal lengths and what they "see"

http://www.shortcourses.com/choosing/lenses/10 .htm

[itinerants]

Thanks vm vehekpfulguy (good user name by the way) - now I understand it.