Focal Length and DSLR

[KJGradwell]

Guys
I have a 300D. I purchased it recently after the prices fell following the release of the 350D. I enjoy reading the posts to your forum(s). I'm learning, although slowly.

I understand (or think I do) that because the optical sensor in a DSLR occupies a smaller area than it's 35mm equivelent that when a lens designed for a 35mm SLR is attached to a DSLR that it's effective focal length is increased by a factor of circa 1.6 i.e. a 50mm becomes an 80 mm.

Questions

Is this true for all DSLRs ( Do some have bigger/smaller optical sensors?)
Is it tue for all lenses ( are some designed specifically for DSLRs) and how do I know which is which?
I can surmise that it's not such an issue with zoom lenses since the range just shifts.
What is the significance with primes does any of this matter?
I'd appreciate any input.
Thanks
kevan

[tim]

To be precise, it's a crop factor, not a magnification. You're not magnifying anything, you're just missing the edges of the picture compared with what a 35mm camera would do. I suggest you ignore that, unless you're a veteran 35mm user, and just know that you put an x-mm lens on and you get whatever sized picture.

1. No, the 1D Mk II has a 1.3 crop factor, the 1Ds Mk II has a full frame sensor.
2. Yes, for all lenses, even EF-S lenses. EF-S are just lighter and smaller because they have less glass.
3. Yep.
4. Same as with any other lens.

Like I said, ignore it, just put lenses on and see what happens.