question about sensor size in digital slr's?

Question

OK..here is a question, just so that I can understand it.

lets say i have a 100 mm lens. As far as I understand things, if I attached this lens to say a canon rebel xti camera which has a sensor smaller than the size of a 35mm camera, it would produce a much different result if I place the same lens on say a canon 5d full size 35mm size equivalent sensor.

So if the smaller chip in the rebel xta results in a 1.6 (converstion, as I have read)

my 100 mm lens now becomes a 160mm on the rebel xti,

BUT wouls still act as a 100 mm on the full sized chip in the
canon 5d??


so my lens focal lenght depends on the size of the sensor???

Answer 1

The focal lenght is always the same and is BTW not the best way to describe a lens.
What you actually see in the pic depends on the focal length of the lens and the area of the ligh sensitive material be it a chip or film.
So with the smaller chip what is in the pic with a 100mm lens is the same as you would see with a 160mm lens on the full sized chip (where full sized refers to the size of 35mm film).
E.g. With a 6x9 cm film camera (old types) a 105 mm lens was a normal lens meaning showing roughly the same as a 50mm would do on a 35mm film camera or on a full size digi chip.
So if a lens acts as a normal lens or as portrait lens (moderate tele) or a tele lens depends on the size of the light sensitive material.
See also the article in the link below

Answer 2

simply by fact the smaller sensor would have greater noise (splotchy crimson and blue dots). there is an extremely thrilling rationalization for this, yet are you a photographer or an electronics geek?

Answer 3

Essentially you're right. The smaller sensors actually 'clip' off part of the picture, so they 'appear' to have zoomed in.