Quote Originally Posted by neuroanatomist View Post
If you put any lens labeled 200mm on your camera, and set it to 200mm if it's a zoom lens, you'll get essentially the same picture. Doesn't matter if it's EF-S, EF, or L.
If this is true, then at least some numbers must be incorrect (converted). As I said before, I’ve been surfing around a lot on this subject and found some images. For example at Wikipedia they have this image:

From this illustration I can see, that EF lens which is made for full frame 35mm cameras gives on APS-C sensor cameras more zoom at the same focal length. Correct?

Another great illustration at BobAtkins:

To get the same field of view as a 28mm lens on the full frame camera, you'd need a shorter focal length lens when used with the APS-C crop sensor. That's illustrated by the green lines in the image above. In the case of EOS DSLRs, the focal length would need to be 17.5mm.
These both images and explanations make sense to me, but I'm really confused by neuroanatomist’s statement. If EF-S and EF lenses give the same results at the same focal lengths, then it means that illustrations above are incorrect. But they look quite logical to me. Still, if both images and neuroanatomist are true, then it means numbers on either EF-S or EF lenses are incorrect. With this theory it means EF-S focal length at 200mm is actually less to project the same image on a smaller sensor. Which means that EF-S lens at 200 mm is actually 200/1,6=125mm and Canon writes on a camera not true focal length, but equivalent of 35mm. Could this be true?