Yes.
Canon EOS film cameras uses EF-mount lenses. All Canon EOS Digital cameras will also accept EF-mount lenses.
yes
Absolutely yes. Canon EOS 450D has the same mount as Canon EOS 400D, wich is EF and EF-S.
Yes, with a FD to EOS adapter.
Some popular Canon film cameras are the Canon EOS Rebel 2000 with 28-80mm lens, Cannon EOS ELAN 7E with 20-90mm lens, and the Canon EOS Rebel G Film SLR Camera kit with 35-80mm lens. You can buy these on any website.
EOS EF-S and EF... The Canon Rebel EOS is compatible with over 60 Canon EF/EF-S lenses A super high-end lens good for this camera would be one of the canon 70 200 lens. You can see a review of it at: http://canonlensreviews.net/canon-ef-70-200mm-2-8l-is-ii-lens-review/
Yes, the Canon EOS 400D has both EF and EF-S lens mounts. Therefore, the TS-E 90mm WILL fit on the camera because it has an EF lens mount.
Yes, you can. Any EF and EF-S lens will work on 20D.
That depends on the lens you put on the camera.
EOS is Electro-Optical System. It controls the optics of a lens through electronic system.
Canon EF-S 17-55 f2.8 is a nice normal zoom lens.
Yes, if you purchase the 'EOS' version of this lens (the one intended for Canon) it will fit just like any other 'EOS' lens would. I have the 500D and it fits fine, but a Google search will show others successfully using the Samyang 8mm fisheye with other Canons e.g. 450D.
yes all Canon cameras are compatible via lenses to each other