[henrynghc]

17-40 4L & 17-55 2.8 is usm其成像,質素 有大分別嗎?
Iam using 500D

[Obi-Wan]

go see

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?FLI=0&API=0&Sample=0&FLIComp=0&APIComp=0&LensComp=100&CameraComp=453&SampleComp=0&Lens=491

[henrynghc]

thanks!

[yiu0920]

請問個網點睇架?

[hcdo]

Dear Mr.Obi-wan,
can you please explain in simple.For I am a beginner,thanks.

[Obi-Wan]

select the input lens, e.g. 17-40, select the body
do this for the next lens
the result will be shown
e.g. If u want to 17-50 vs 17-40 on 50D @ f4 and 17mm
the result is
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=398&Camera=474&Sample=0&FLIComp=0&APIComp=0&LensComp=100&CameraComp=474&SampleComp=0&FLI=0&API=1

u move the mouse across the frame, of the black white lines, will can compare which one is better, the result shows

the upper part (= center of an image)
u can see the lines are sharp at the no. 28 for the 17-55 & 30 for the 17-40, this show that image sharpness is more or less the same for the 2 lenses with the the 17-40 wins a little bit

the lower part (= corner of an image)
the 17-55 is definitely much better than the 17-40

[Obi-Wan]

u can also check
http://www.xitek.com/info/showarticle.php?id=1689

for details of the ISO 12233 chart meaning

[hcdo]

Mr. Obi-Wan,thanks a lot.