EF-S 17-55mm f/2.8 IS USM - Focal Length Confusion

ryllz wrote:

Hi All,

I am very new to DSLR photography and have just recently purchased the T4i with the 40mm 2.8 lens.  To upgrade the lens kit that came with my camera 18-55, I am contemplating purchasing the 17-55 2.8 based on all the reviews I have read here and other sites.

My question is this: If the EF-S 17-55 was specifically made for the APS-C DSLRs and is not compatible with the FF cameras then why would the equivalent focal length still be at 27-88mm on the APS-C DSLR??  This confuses me a whole lot and i've read quite a bit.  I still have not found the explanation.

Based on my question above then what type of camera should I buy to take advantage of the actual 17-55mm focal length that I am planning to buy (obviously not an APS-C and this does not work on a FF so what are my other choices??)

Please forgive this very amateur question but it confuses me to no end.

Thanks in advance for the responses.

Ryll

I think that the confusion is in that the equivalence is, in part, for people whose reference is to film and full frame.  For some people moving from film to APS-C, the conversion helps them to understand the field of view.  17-55 on a crop camera (APS-C) provides the same field of view as would a 27-88 on a full frame or 35mm film camera.    If you took an image using 35mm or full frame camera and a 50mm lens, the same image (using the same lens) from an APS-C camera would look as if the full frame/film image had been cropped...equivalent to taking the same image on a full frame/35mm camera with an 88mm lens....distance form subject being constant.  Thus APS-C cameras are called crop cameras.  You have the right camera for the 17-55. It just helps some folks moving from 35mm to know that the "crop factor" is 1.6, and that a lens, for instance the 17-55, provides the equivalent that a 27-88 lens  would on a full frame/35mm camera (although no one makes that focal range, nearest is 24-70).

Enjoy the 17-55 - it is indeed an excellent lens.

Best,