Is an Ef 24mm angle as wide as an EF-S 24mm angle when mounted on a cropped frame?

Remember, an EF 24-105 mm on a "cropped" camera body (such as the 4Ti) is actually a 38.4mm x 168 mm focal length lens. Therefore, the FOV with the lens set to 24mm on the full frame camera would be different than the FOV with the lens set to 24mm on the "cropped" body camera. As I understand it (and boy, could I be wrong!) as the focal length changes so does the field of view. The EF-S lens is simply a lens that will only fit onto the cropped body camera, not the full frame. Nevertheless, at 24mm, the lens focal length is still actually 38.4mm, not 24mm. Therefore, see above.

Hi all,

I finally got my canon 17-55 :D

I took a couple of picture soon after unboxing the lens and came to realise that this was the lens i was looking for.

I liked the instant and ultra silent focusing, its sharpness and liked the fact that this lens is not as bulky as I had imagined it to be. But most of all, I loved the fact that I could carry on taking pictures in lower lighting conditions.

With regard to colour, it remains to be seen if, as frequently stated in many lens reviews, this piece of glass reaches the standards achieved by other L series lenses, such as the 24-70. Truth be said, I use an old 350D and my computer screen is not calibrated, so I cannot really tell. However, when i adjusted the white balance of some of the images that i took on adobe bridge, I managed to achieve that pop out effect, which I believe is the direct result of high-quality lenses.

Having that said, i found out that when the focus ring reaches either end, the rubber piece on the outside keeps 'loosely' turning. Is this normal? This surprised me a bit, coming from a relatively high-end camera.

The "loose" focus ring is part of the USM with FTM (Full Time Manual Focus). You can always turn the focus ring, even while AF is on, that's why it has to be loose so that you don't accidentally work against the AF motor.

Oh so that's the reason why it feels kind of 'loose'.

Well, now I can proceed with giving the thumbs up to ebay seller who sold me the lens.

Many thanks ahab1372 and all the others for your kind advise.

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Originally Posted by Steve in HB

As I understand it (and boy, could I be wrong!) as the focal length changes so does the field of view. The EF-S lens is simply a lens that will only fit onto the cropped body camera, not the full frame. Nevertheless, at 24mm, the lens focal length is still actually 38.4mm, not 24mm. Therefore, see above.

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Boy, you are wrong... :) At least partially. Now if the focal length actually did change, then the field of view would change accordingly. However, the focal length can't change, since it's a physical characteristic of the lens itself. It has nothing to do with the camera it's mounted on. Instead, the field of view changes because the smaller sensor in the APS-C camera doesn't see as much of the subject as a full frame sensor would, if it was sitting behind the same lens. This is the same as would happen if you look at something with your naked eye, then look at the same thing through the core of a toilet paper roll. In the second case you see far less, but nothing has changed inside your eye. Regarding lenses not really having the focal length they are marked with, the EF-S 17-55 mm f/2.8 IS USM is a known offender. The wide end is more like 18 mm than 17. At these focal lengths, the difference of 1 mm is quite noticeable. As far as focusing goes, the 17-55 mm would rather be better than the EF-S 15-85 mm f/3.5-5.6 IS USM, since the max aperture of f/2.8 allows the center point to use the high-accuracy sensor pairs instead of just the regular ones.

Think back to the days of slide film (or read about it on Wikipedia...). Remember the little white cardboard frames to mount each slide? Imagine holding one of those up near your eye and looking through it:

The outside "rectangle" is analogous to how big the sensor would be for full-frame cameras.
The inside "rectangle" is analogous to how big the sensor would be for crop-frame cameras.

EF lenses are lighting up the whole outside rectangle during the shot, but the crop-frame sensor is "discarding" the cardboard portion.
24mm is still 24mm. However, EF-S lenses don't bother to (always) cast light on the "discarded" portion.