17-40L vs 18-55 reach vs crop

[scott_milso]

If you needed all the reach you could get, which would produce a

better photo the 18-55 at 55mm f/5.6 OR the 17-40L at 40 then cropped

to equal the 55's reach at same f stop?

I understand there's a difference between crop and focal length in

terms of perspective.

[peter_white2]

I think I'd rather use the 17-40. Of course the only time the cropping would be an issue is if you were printing very large. At 8x10 you should be pretty close to full res with the lens at 40mm.

[mormegil]

Actually, there is no difference between crop and focal length when it comes to perspective.

 

Perspective is purely a function of distance from the subject.

 

The reason you tend to get different perspectives with different focal lengths is because you change your distance to fill the frame, which changes your perspective.

[mendonphoto]

Two important variables: aperture & contrast.

 

I'd take the 18-55mm at 55mm and f/11 and no direct sunlight (or other potential for flare) over any 40mm cropped. But, I'd take an expensive lens at 40mm, f/5.6 (or faster), and with sun in the frame over the 18-55mm even if I had to crop to an equivalent focal length of 55mm.

[extreme artists]

I would use the 17-40 and get closer, if I couldn't I would stich the 24-70 on.

[jeff_d]

the 18-55 is reportedly such a piece of junk that i would not deal with it. i have the 17-40L, and on a 20d, it is sharp as a tack. If softness is an issue, i would always use the L, or just buy a 50 prime, thier cheap.

[dogbert]

an example of what you get with such a piece of junk.

[jeff_d]

one good exposure doesnt prove anything to me, but i will admit it looks like a good exposure. From what i have read about it has been absoloutely horrible. i will still put it up against the L any day even without using it. There frankly is not going to be any comparison. the only thing going for it is its price. I dont think you can even buy it on its own.

 

http://www.photo.net/equipment/canon/efs18-55/