A recent discussion at a popular web site reveals the continuing confusion over the differences between Canon EF and EF-S lenses. Bad advice from camera stores does not help.<\/p>\n
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Here is part of the question:<\/p>\n
I’ve been told that the EF lenses will fit the EF-S mount, but that some sort of calculation will have to be applied to offset the shutter speeds or aperture settings. I don’t understand this and was wondering if it was just something my local camera shop told me to get me to cough up more money for EF-S lenses. Can anyone enlighten me? <\/em><\/p>\n Some of the answers that followed the question were helpful, and some were just plain wrong. I am asked similar questions on a frequent basis, so I thought it would be helpful to post my answer to the above question:<\/p>\n You don’t have to recalculate exposure in terms of apertures and shutter speeds with either EF or EF-S lenses. And the field of view of equivalent EF or EF-S lenses will be the same on the same digital camera body, so you don’t have to recalculate that either. A 30mm EF lens will give you the same field of view as a 30mm EF-S lens, provided they are on the same camera body. The advice from the camera store is suspicious.<\/p>\n One difference between EF and EF-S lenses is mechanical. EF-S lenses will not fit on some EOS digital bodies (like the D30, D60, 10D, and 1D series cameras). Don’t confuse the D30 with the 30D. (What was Canon thinking with such similar names?) EF-S lenses don’t fit on EOS film bodies either.<\/p>\n EF-S lenses will fit on the Canon 20D, 30D, and the recent digital Rebels. Canon digital cameras that take EF-S lenses have a white square next to the red circle on the lens mount surface. EF-S lenses also have a white square for alignment purposes when mounting the lens on the body.<\/p>\n EF-S lenses are optically different in that they project a smaller image circle than EF lenses, but that won’t matter at all on any Canon body it is designed (mechanically) to fit (more at the link below).<\/p>\n EF lenses fit on all EOS film and digital bodies. Even though the image circle of EF-S lenses is smaller than EF lenses of the same focal length, the equivalent focal lengths are the same. In other words, a 50mm EF lens and a 50mm EF-S lens have the same focal length (despite the difference in the size of the image circle – more info at the link below).<\/p>\n The focal length of a lens does not change whether you put the lens on a film camera, a “full frame” digital camera, a digital camera with a smaller image sensor, or even a medium or large format camera. A 50mm focal length lens is always a 50mm focal length lens no matter what camera you put it on. Field of view is another matter.<\/p>\n A smaller sensor digital camera, like all the the Canon D-SLR bodies (except for the Canon 1Ds and 5D which are “full frame”) will not show as much of the image circle as a 35mm film camera (or a full frame digital camera) so the field of view is cropped, or smaller. A 50mm lens on a small sensor Canon D-SLR has the same field of view as an 80mm lens on a 35mm film camera, so it LOOKS like the focal length changed. The focal length of the lens didn’t change at all. Just the cropping of the image. This is usually called the field of view (FOV) crop.<\/p>\n