EF verses EFS?

I am in the midst of obtaining a new rebel xt body and wondering about the EF"S" designation?

EF lenses works for any camera (1D's, 5D, 300D/350D/400D and 10D/20D/30D, etc).

EF-S lenses only works for 300D/350D/400D and 10D/20D/30D.

What actually makes the difference of the EFS though?

The EFS' stick into the camera further than an EF. They will interfere with the movement of the mirror if used on a FF camera.
I think the S stands for "short," as in a short er distance 'tween the glass and the sensor.

EF-S DOES NOT work on the 10D.

why would they make a S lense then if many just use EF anyways?

Aside from the physical constraints, the EF-S lenses produce a smaller image on the sensor---big enough for the 1.6X cameras, as Petra already stated. However, even if they are altered to fit in a 1.3X or 1X body (1D, 1Ds, 5D), there would be serious vignetting of the image.

I recall when the first Rebel was introduced (300D), people were cutting off the projection on the back of the lens so they would fit all models. Nutty!

Because of the 1.6 crop factor on Non-full Frame cameras... Becasue your working w/ a FOV of 1.6x a Lenses Focal Length, the EF-S lenses try to bridge a gap in popular, traditional Full Frame Focal Lengths.

Example.
A EF 16-35mm f/2.8L on a rebel has a FOV of 25.6-56mm
But on a Full frame it is a true 16-35mm
So the EF-S 10-22mm Has a FOV of 16-35mm

But I'm not sure the information above is correct.
EF-S work on the 350D, 400D, and 20D. I'm not sure about the 30D
They do not work on a 10D

slyone wrote in post #2256246
why would they make a S lense then if many just use EF anyways?

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 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 mount is different 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. Also, the 35mm film frame would have a dark circle around the edges and the image inside the circle.

Now that you have some understanding of what the EF-S lenses are all about, note that there are NO long lenses with the EF-S design as they simply aren't needed. They would duplicate EF series lenses that already do quite well on APS-C camera bodies.

An additional tidbit - focal length is focal length, regardless of the format of the camera (film frame or digital sensor size) the lens may be attached to. A 50mm EF lens will provide precisely the same image when mounted to an XT as an 18-55mm "kit" lens adjusted to be at 50mm mounted on the same XT body.

EF-s Lenses are worthless to me!
I can't use them on either DSLR I own
Oh well

John_B wrote in post #2256424
EF-s Lenses are worthless to me!
I can't use them on either DSLR I own
Oh well

You could with judicious application of a hacksaw to the back of the lens.

slyone wrote in post #2256177
What actually makes the difference of the EFS though?

Two things, firstly the image circle will only cover the APS-C sensor and will cover a full frame camera like the 5D.

Secondly, the S stands for short back focus, the means the lens rear element can stick too far back to be used on earlier cameras as it will interfer with the mirror movement. The EF-S lenses will not mount onto a full frame camera or early APS-C cameras that are not compatible.

However all cameras can use the EF lenses, so many working with APS-C cameras have plans to move to a full frame camera at some point and so shun the EF-S lenses.

On the plus side the EF-S lenses tend to be smaller and lighter than the EF equivalent, but not obviously cheaper. There are some very good EF-S lenses like the 10-22, 60mm macro and the new 17-55 f2.8 IS, the others are more of the level of comercial zooms.

The one lens that can not be covered in some way by EF lenses is the EF-S 10-22.

slyone wrote in post #2256246
why would they make a S lense then if many just use EF anyways?

Simply because it is cheaper to make lenses with smaller image circles.

For example, if they can make a 35mm EFS with a smaller image circle coverage and call it a 'normal lens' for the APS-C format camera, and offer it at a lower price than the 35mm EF lens, it makes some sense especially if they can also save in other areas of production cost.

In the case of wide angle lenses particularly, where shorter focal lengths are needed wtih APS-C to achieve the same field of view as FF cameras, EFS makes the most sense. Steller performers like the 10-22 EFS would probably be absurdly expensive if it had to have an image circle large enough to accommodate 35mm film and FF dSLR!

The EF-S mount does two things.

First, it allows the rear lens element to be positioned closer to the sensor which is an advantage when designing lenses for a small sensor, especially for wide angles, but also for zoom lenses.

Second the EF-S mount prevents mounting the lens of EF only cameras. The image circle is not big enough to cover a full frame sensor and the position of the rear element could cause contact with the mirror when it flips.

Thanks everyone for your perspectives! I know nada! Have a xt coming today and have been looking at the vast array of products(lenses) available, that's all. My neighbor offered to sell me his nifty 50 f/1.8 w/uv and neutral density for 65.00. I also have a 100.00 credit w/Dell (whose lenses are already inflated 30%!) will be needing a 200-300 zoom for next year's HS football and soccer games(the dreaded Friday night/low light) I currently use the Pro1 P/S 28-200Lf/2.4-3.5