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Old Sep 1, 2005, 11:28 AM   #21
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NHL wrote:
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This comparison has been posted many times already:
http://www.stevesforums.com/forums/v...mp;forum_id=65

... and with their respective MTF's:
http://www.stevesforums.com/forums/v...mp;forum_id=65
The thread linked above not say anything like "the 17-85 is considerably better sharpness wise than the 17-40". And the MTF doesn't show that either, not least because it doesn't contain a sharpness curve for the 17-40. The contrastis also not clearly superior, and you could read the 17-40 contrast curve at 17mm, f/8 as being clearly superior.

Moreover, can anyone confirm the source and accuracy of the 17-85 MTF? - because that's not on Canon's US or UK sites at this time. (I even tried Canon's Japan site, but could only find the lens, not its MTF.)

If the 17-85 is "considerably better sharpness wise than the 17-40", then it should be easily and often demonstrated with sample pictures -- where are they?
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Old Sep 1, 2005, 11:41 AM   #22
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Here's the EF-S 17-85mm: http://www.canon.com.hk/En/Product/P...p;tag_id=10515

and here the EF 17-40mm: http://www.canon.com.hk/En/Product/P...p;tag_id=10161

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Old Sep 1, 2005, 12:28 PM   #23
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Madwand wrote:
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The contrastis also not clearly superior, and you could read the 17-40 contrast curve at 17mm, f/8 as being clearly superior.
I don't know about you but I see a BIG difference here:
(the sharpness curves if plotted are always below the contrast curves)




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Old Sep 1, 2005, 12:40 PM   #24
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Hunting some more on Canon Japan's site, I was able to find the pages for both lenses, including full MTF's.

http://cweb.canon.jp/ef/lineup/wide_...f4l/index.html

http://cweb.canon.jp/ef/lineup/ef_s/..._56/index.html

Here are the zoom-ins for the MTF curves:

http://cweb.canon.jp/ef/lineup/wide_...0_f4l/mtf.html

http://cweb.canon.jp/ef/lineup/ef_s/...f4_56/mtf.html

Points to note:

The previous MTF's for the 17-40 did not show any sharpness curves, so as far as I'm concerned, arguments about it being "considerably sharper" on that basis were flawed.

Japan's contrast curves for the 17-40 are significantly better wide open, explaining why the US and HK, partial MTF curves look so funny in that regard (for an f/4 lens). This also brings into question why the curves are different in different countries and adds some doubt about their overall accuracy.

Comparing the 17-40 and 17-85 at the telephoto ends is silly --you'd get muchmore realistic and meaningful results by comparing the 17-85 at 85 with 70-200 f/4 L at 70.

In comparing the 17-40 and 17-85 in detail at 17mm, I see only aspect in which the 17-85 is slightly superior -- meridonial sharpness wide open at the edge (around 0.66 vs. 0.69). In most other respects, including saggital performance wide open and performance at f/8, the 17-40 is superior. You need to be careful to compare performance at 13, not at 15 on the 17-40's curves for these nit picks.

http://luminous-landscape.com/tutori...ding-mtf.shtml

I think that these results are remarkable, in favour of the 17-85 as the underdog being so close to the 17-40, but saying that the 17-85 is "considerably sharper" is false and a gross exaggeration.

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Old Sep 1, 2005, 2:14 PM   #25
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Madwand wrote:
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Comparing the 17-40 and 17-85 at the telephoto ends is silly --you'd get muchmore realistic and meaningful results by comparing the 17-85 at 85 with 70-200 f/4 L at 70.
I agree 100% and already have noted to that fact in the same post last year:
"but IMO only the left charts should be compared, with the right charts: one tele is twice the range of the other and it's like apple and orange comparison there, plus that's a pretty good MTF considering the 2nd one is an 'L'!"
http://www.stevesforums.com/forums/v...mp;forum_id=65




Quote:
The previous MTF's for the 17-40 did not show any sharpness curves, so as far as I'm concerned, arguments about it being "considerably sharper" on that basis were flawed.
Not really if all you had at the time was the MTF from the other Canon site - The contrast of the EF 17-40 there was already at the same level as the sharpness curve of the EF-S 17-85... Wonder why the sharpness curve wasn't plotted: if it was higher (a miracle) then Canon would have advertised it would they? At 10-40 (vs 5-10) lp/mm reading the sharpness curve is bounded to be below the EF 17-40 contrast curve (which is below the EF 17-85 sharpness curve)...


The point is well taken though based on the new set of MTF curves (good find) - Correction noted!
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