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by E.J. Peiker on Mon Mar 24, 2008 8:09 pm
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You can see that the 100-400 data is very suspect as it only attains maximum sharpness dead center and falls off in dramatic fashion immediately as you move away from center. By the time you are only 5mm from center, the lens already has significantly poorer performance than any other. The others don't do this and even the 300/2.8 with 2x holds up much better. It also suggest that this would be a highly variable lens since repeatability of something so close to the edge of a major performance drop off in the center would be very susceptible to even the slightest manufacturing variances. I have worked with lenses that have this charachteristic in photolithography over the years and they have very poor repeatability and require constant tuning to give acceptable results.
 

by Ed Cordes on Mon Mar 24, 2008 8:23 pm
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While I am certainly not an expert on these charts, it seems that the 100-400 produces worse bokeh than the prime.

Thanks E.J. for starting this interesting thread.
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by liquidstone on Mon Mar 24, 2008 10:35 pm
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Scott Fairbairn wrote:So from the MTF charts, the 100-400 is better in the center of the frame than the f5.6 prime AND the 300 +1.4x ???

From my reading of Canon's MTF charts, the 100-400 should outperform the 400 5.6L in the center of the frame at 400 mm wide open in all respects except bokeh. Whether that's true in real life with all or most copies of the 400 zoom and prime is IMHO the bone of contention. Many users and testers of both lenses come out with differing experiences, and admittedly, many of these are in favor of the prime.

I submit however that the possibility of an optimal copy of the zoom matching an optimal copy of the prime at 400 mm f/5.6 (except bokeh) is there..... it might not be probable, but certainly possible.


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by Cameron Galle on Mon Mar 24, 2008 10:48 pm
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Ok - what are the x & y axis on these charts? & what's with the multiple lines... a chart without a key is one of my bugbears...
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by E.J. Peiker on Mon Mar 24, 2008 10:51 pm
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The x axis is distance from center so 0 is dead center, the y axis is a representation of the capability of resoving line pairs. 1 is perfect, and 0 is no resolution at all.
 

by Gray Fox on Tue Mar 25, 2008 7:52 am
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Cameron Galle wrote:Ok - . . .what's with the multiple lines... a chart without a key is one of my bugbears...
Canon's EF Lens Work, Optical Terminology & MTF Characteristics contains an explanation of their MTF charts, which are calculated rather than measured. See pages 202-203 and page 209. The curves labeled "S" (solid curve) represents lens performance in the sagittal direction, i.e. radial outward from center, and the "M" lines (dashed curve) represents performance in the meridional orientation, sometimes called tangential. Think concentric circles, at right angles to sagittal. The table of contents for the entire book may be found at EF Lens Work III
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by Patrick Cox on Tue Mar 25, 2008 8:08 am
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Thanks for the link Michael.

Can someone tell me the point of the M lines vs the S lines? Why do you need two line orientations and what performance difference do they depict? (I understand that the S lines and the M lines are perpendicular to one another but I don't understand what that tells you about the lens.)

I noticed that the dashed lines (S I believe) seem to fall off faster than the solid (M) lines.

Thanks!
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by Gray Fox on Tue Mar 25, 2008 9:15 am
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Patrick Cox wrote:Can someone tell me the point of the M lines vs the S lines? Why do you need two line orientations and what performance difference do they depict? (I understand that the S lines and the M lines are perpendicular to one another but I don't understand what that tells you about the lens.)

I noticed that the dashed lines (S I believe) seem to fall off faster than the solid (M) lines.
Patrick, the short answer is that both are provided because, based on the realities of optics, they are likely to be different. It is a relevant point because sometimes people gloss over those pesky little dashed meridional lines, the ones that usually lie below the solid (sagittal) curves. For a typical subject that contains elements oriented every which way, the performance of the lens is some complex function of both sets of lines, i.e. performance lies between the two curves, not at the top one. For another explanation of MTF, see Michael Reichmann's Luminous-Landscape Understanding Series article on MTF: Understanding MTF There's also a useful archived thread on sagittal vs meridional MTF on Photo.net: Photo.net Sagittal vs Meridional MTF thread, especially Struan Gray's explanation about 10 or 15 posts down.
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by Ed Cordes on Tue Mar 25, 2008 11:57 am
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So, taking into account the rate at which the dotted lines fall off on the zoom compared to the prime and Michael's comment above re "For a typical subject that contains elements oriented every which way, the performance of the lens is some complex function of both sets of lines" we can see why the zoom does not produce images that appear as sharp as the prime.
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by GeneO on Tue Mar 25, 2008 8:21 pm
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Well speaking of anecdotal, the MTF have at best a loose connection with reality - they are based on theoretical models of the lens, and not measurements. They also don't take into account the quality of production or sample variation. In additon, everyone always seems to ignore the meridonal curves, which are just as important as the sagittal, and these are worse for the 100-400.

I believe there is a lot of sample variation in the zoom, partly because of its type of construction. I have owned both and was the recipient of one of the softer copies of the 100-400 (at 400mm wide open). I could never use it wide open with confidence.

If you did a sample of both the priime and the 100-400, for example looking at FM reviews, I wager you will see lots of reports of "soft" 100-400, and virtually none for the 400/5.6L. Having said that I think there is a little bit of a bias against the 100-400 because it is the pototypical wildlife starter lens, and thus some of those "soft" reports are attributable to user error. However I have known quite a few experienced photographers, besides myself, that have had honest-to-god "soft copies" @ 400mm/f5.6.

What I do hear from many, which is purely anecdotal, is that newer 100-400 are of better quality because Canon has improved QC on their production. I am suprised somebody didn't state that here :)


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by Tsmith on Tue Mar 25, 2008 10:42 pm
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Awesome job on this EJ. Now makes me reconsider the 300 f/4L IS _ :?
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by Steve Mason on Wed Mar 26, 2008 1:33 pm
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I just picked up my 400 5.6, cue the bad weather.
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by bjs on Thu Mar 27, 2008 7:15 pm
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GeneO wrote:...everyone always seems to ignore the meridonal curves, which are just as important as the sagittal, and these are worse for the 100-400...
I'm not sure the data supports your assumption. According to Photozone, the center sharpness measures at 1670 and the border sharpness at 1592. This is only a 5% reduction which matches the sagittal lines MUCH better than the meridonal ones.
 

by GeneO on Thu Mar 27, 2008 7:54 pm
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bjs wrote:
GeneO wrote:...everyone always seems to ignore the meridonal curves, which are just as important as the sagittal, and these are worse for the 100-400...
I'm not sure the data supports your assumption. According to Photozone, the center sharpness measures at 1670 and the border sharpness at 1592. This is only a 5% reduction which matches the sagittal lines MUCH better than the meridonal ones.
And exactly how do they measure the sharpness?
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by Royce Howland on Thu Mar 27, 2008 8:02 pm
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It's not surprising that the Photozone lp/ph measurements track the sagittal lines on the MTF chart. As I understand it the data values come from using Imatest to analyze a test chart that consists essentially just of radial type lines, which is also what the sagittal MTF line is based on. The meridional MTF line involves concentric lines centered on the optical axis; these are not part of the test chart used by Photozone from what I can tell...

http://www.photozone.de/lens-test-faq
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by GeneO on Thu Mar 27, 2008 8:03 pm
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Exactly :)
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by Patrick Cox on Thu Mar 27, 2008 8:53 pm
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I am out of my league in this technical discussion but doesn't photozone also use 1.6x crop cameras only for testing and Canon's MTF charts are most likely based on a FF 35mm sensor size. This would account for some difference in edge falloff as well I believe.

Pat
 

by E.J. Peiker on Thu Mar 27, 2008 9:12 pm
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Patrick Cox wrote:I am out of my league in this technical discussion but doesn't photozone also use 1.6x crop cameras only for testing and Canon's MTF charts are most likely based on a FF 35mm sensor size. This would account for some difference in edge falloff as well I believe.

Pat
Yes, which makes PZ tests invalid for anyone using a 1 series or a 5D - I pointed that out about 4 pages ago :lol: ;)
 

by bjs on Thu Mar 27, 2008 10:15 pm
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Royce Howland wrote:It's not surprising that the Photozone lp/ph measurements track the sagittal lines on the MTF chart. As I understand it the data values come from using Imatest to analyze a test chart that consists essentially just of radial type lines, which is also what the sagittal MTF line is based on. The meridional MTF line involves concentric lines centered on the optical axis; these are not part of the test chart used by Photozone from what I can tell...

http://www.photozone.de/lens-test-faq
I believe you are incorrect Royce. The test target in their link is not oriented in the sagittal direction. Rather it is oriented to be halfway inbetween sagittal and meridional orientation (ie 45degrees to both) and thus responds to both.
 

by bjs on Thu Mar 27, 2008 10:29 pm
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E.J. Peiker wrote:
Patrick Cox wrote:I am out of my league in this technical discussion but doesn't photozone also use 1.6x crop cameras only for testing and Canon's MTF charts are most likely based on a FF 35mm sensor size. This would account for some difference in edge falloff as well I believe.

Pat
Yes, which makes PZ tests invalid for anyone using a 1 series or a 5D - I pointed that out about 4 pages ago :lol: ;)
No. Since APS sized cameras are smaller than 35mm, one only has to ignore the extra information that Canon's lense charts provide. Pat's concern is not a factor here, just map the Photozone numbers to the correct point(s) on the MTF graph.
 

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