Difference betweet EF & EF-S Lens

I see that the EF-s Lens are for Digital cameras but what is the big difference between the two? Is one better than the other?

The S is for "short back focus" which means in practical terms that the image circle is only sufficient to cover the smaller sensors of the XXd/XXXd lines (20D-40D/300-400D) and will only mount to these cameras.

Unless you intend on upgrading to a 1-series or full-frame 5D you'll probably never notice a difference... at this stage there are no EF-S lenses designated as "L" but look at the quality you get out of a 10-22 or 60mm macro and man, they may as well be apart from the weather-sealing and build quality

The APS-C cameras have a smaller sensor than a 35mm film frame. If you limit the lens selection to those lenses designed to fill a 35mm frame (such as Canon’s EF series lenses), you will find that there are no ultra-wide-angle lenses for the APS-C camera. The shortest zoom lens focal length in the EF lens family is 16mm. There are two primes that are a bit shorter, and one of those is a "fisheye" lens. NONE of these lenses are what the average photographer would call "affordable".

To design an ultra-super-wide-angle lens such as a 10mm (non-fisheye) lens for a 35mm camera is a VERY expensive proposition, which is why there are none.

By making some changes to the design criteria - reducing the "film" area to be covered by the lens, and allowing the lens to project deeper into the mirror box (move the rear element of the lens closer to the "film"), it becomes much more economically possible to design lenses for the task. Thus, the EF-S family of lenses was born, the “S” standing for Short back focus. The EF-S lens mount is purposely designed to be different from the standard EF lens mount so that you cannot mount the EF-S lenses on cameras that were not specifically designed for them. If you modified the mount of an EF-S lens to be able to put it on a 35mm film camera, there would be a high probability that the mirror would crash into the rear element of the lens at certain focal lengths (the mirrors in the APS-C cameras are significantly smaller than those in 35mm cameras and “full-frame” DSLR’s). Also, the 35mm film frame would have a dark circle around the edges and the image would be inside the circle (known as severe vignetting).

Now that you have some understanding of what the EF-S lenses are all about - note that there are no long focal length lenses with the EF-S design as they aren't needed - you need to understand that focal length is focal length is focal length. An EF 50mm prime lens designed for a 35mm camera, when used on an APS-C camera, will provide you with EXACTLY the same image size as an EF-S 18-55 lens set to 50mm. If you could cobble together a mount for a Hasselblad 50mm lens and use it on a 20D, you would again have the same size image as a result.

NO CHARACTERISTIC of any lens changes when you mount it on different format cameras. Focal length (or focal length range for zooms) never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image.

EF-S lenses, by the way, will only fit on the Digital Rebel series cameras (300D, 350D, and 400D), the 20D, 30D, and the 40D as of this writing.

As Skip said, EF-S lenses take advantage of small image circle and closer back focus to provide short focal length lenses without breaking the bank. These shorter focal length lenses are very much needed incidentally on smaller format cameras as the typical ranges offered for 135 format are not wide enough on the smaller format.

A 17-40 is an ultra wide lens on 135 format, and there were (prior to EF-S and 3rd party equivalents) no options at all for APS-C until the various 10-XX lenses arrived.

A 24 or 28 - XX zoom is your basic wide to normal zoom on 135 format, which is an unsatisfying range on APS-C. Early 10D shooters pressed the 17-40L into service to replace this much needed range until the EF-S 17-55, 18-55 and Tamron 17-50 arrived on the scene.

OK, Thanks for the great info. I would guess then buy the ranges you need in the ef-s series lens that you want to use then when you get the $$ buy the "L" series then. I have a rebel right now and was just told that I am getting a XTi sometime in the next month as a gift. I do not shoot enough yet to justify a EOS-5D yet but would like to consider purchasing one within the next 2 years. I did not understand the differences between the two, until now, but want to spen my money wisely also with looking at the future.

Don't underestimate the EF-S 17-55 and EF-S 10-22. Canon won't put a red ring on an EF-S lens but these two are optically stellar. Also don't make the mistake of thinking an L lens is needed in all situations. Many non-L prime lenses are more than adequate.

Yes, two formats in the Canon range can be a little bit of a pain. If you are dead sure of getting the 5D in the very near term then you might want to buy lenses with an eye towards using them on the 5D later. But then....it might be better to just save up and try to get the 5D first. Even if you buy a lens like the 17-40L now (making a passable wide to normal zoom) it will fulfill a totally different role (ultra wide angle zoom) on a 5D so your total lens kit would need a big re-juggle if you change regardless.

If the 5D is only a distant maybe, be careful shunning smaller format lenses. Doing so will cost you the ultra wide range and force compromises on your most used wide to normal range.

It might be better to keep in mind that 1. You can sell lenses just like you can sell bodies when you change formats and 2. You might find you can do everything you need on an APS-C body for years to come.

SkipD wrote in post #4289163
The APS-C cameras have a smaller sensor than a 35mm film frame. If you limit the lens selection to those lenses designed to fill a 35mm frame (such as Canon’s EF series lenses), you will find that there are no ultra-wide-angle lenses for the APS-C camera. The shortest zoom lens focal length in the EF lens family is 16mm. There are two primes that are a bit shorter, and one of those is a "fisheye" lens. NONE of these lenses are what the average photographer would call "affordable".

To design an ultra-super-wide-angle lens such as a 10mm (non-fisheye) lens for a 35mm camera is a VERY expensive proposition, which is why there are none.

By making some changes to the design criteria - reducing the "film" area to be covered by the lens, and allowing the lens to project deeper into the mirror box (move the rear element of the lens closer to the "film"), it becomes much more economically possible to design lenses for the task. Thus, the EF-S family of lenses was born, the “S” standing for Short back focus. The EF-S lens mount is purposely designed to be different from the standard EF lens mount so that you cannot mount the EF-S lenses on cameras that were not specifically designed for them. If you modified the mount of an EF-S lens to be able to put it on a 35mm film camera, there would be a high probability that the mirror would crash into the rear element of the lens at certain focal lengths (the mirrors in the APS-C cameras are significantly smaller than those in 35mm cameras and “full-frame” DSLR’s). Also, the 35mm film frame would have a dark circle around the edges and the image would be inside the circle (known as severe vignetting).

Now that you have some understanding of what the EF-S lenses are all about - note that there are no long focal length lenses with the EF-S design as they aren't needed - you need to understand that focal length is focal length is focal length. An EF 50mm prime lens designed for a 35mm camera, when used on an APS-C camera, will provide you with EXACTLY the same image size as an EF-S 18-55 lens set to 50mm. If you could cobble together a mount for a Hasselblad 50mm lens and use it on a 20D, you would again have the same size image as a result.

NO CHARACTERISTIC of any lens changes when you mount it on different format cameras. Focal length (or focal length range for zooms) never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image.

EF-S lenses, by the way, will only fit on the Digital Rebel series cameras (300D, 350D, and 400D), the 20D, 30D, and the 40D as of this writing.

Not entirely, Skip.

With lenses designed for larger formats you use only the central, best corrected part, generally, of any lens. That's the good news.

However when using lenses which are designed for a much larger format, resolution is less than it would be for a much smaller format, because resolution is, amongst others, linked to image size. Between APS-C and FF it doesn't matter much, because we haven't run into real physical resolution limits yet, but it can make a difference with, e.g., MF lenses, and will make a difference for sure with lenses for even larger formats .

Kind regards, Wim