With the EF-S lenses do you still have to use the 1.6X factor with the 20D or if a EF-s says 20mm then it is 20 mm???

You still use 1.6x for the conversion factor.

You still apply the crop factor. The digital lenses reduce the image circle by cropping, not by reducing the magnification.

So if I buy a 20mm EF-s Lens will it appear the same as a 20mm lens on a 35mm SLR. will it be just as wide??

A 20mm EF-S lens (say for your 20D) will functionally serve similarly as a 32mm focal length on a standard 35mm film camera.

20 x 1.6 = 32

However, keep in mind that you are NOT getting a longer focal length and you are not "zoomed in closer" - the sensor is smaller and simply recording less of the overall "image" as compared to what a 35mm film camera would capture.

In other words... It is still a 20mm lens... you have an increase in the perceived focal length by using the 20mm on a DSLR rather than a Film SLR. (It's simply a 20mm lens on a digital sensor that is smaller than the equivalent technology used in a standard 35mm film camera. )

Does that make more sense than all the tech talk?

Just take a few steps backwards and you will never notice the difference.

CDesperado wrote:
True, but the implications of all of that are not particularly obvious.

http://www.stevesforums.com/forums/v...25&forum_id=65

http://www.photo.net/learn/optics/dofdigital/

For most purposes there's little harm in simply multiplying by 1.6 to get the 35mm equivalent and leave it at that.

With the proliferation of different sensor sizes I'm actually in favour of starting a movement whereby we quote the angle-of-view of the lens instead of the focal length.