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Archive 2012 · 16-35L II DOF observations
  
 
Daan B
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p.1 #1 · 16-35L II DOF observations


I was comparing the 24-105L, 35L and 16-35L II at comparable focal lengths / apertures. One thing I noticed is that the 16-35L II has a much shorter DOF for a given aperture when compared to the other lenses. It also seems that the DOF lies a bit more forward, whereas the DOF with the 24-105L and 35L is more to the back. There are no AF calibration issues. The center is sharp for all lenses. MF and AF give the same results.

Another thing that is really weird is that 28mm the 16-35L II has really sharp extreme corners and center, but the area in focus that lies in-between is relatively soft. So, the extreme corners are sharper than the corners It almost looks like at 28mm there is so much field curvature that the area in focus has the shape of half a circle: sharp in the center and then dropping off to the extreme corners very rapidly.

I wonder what is going on here?



Aug 03, 2012 at 12:48 PM
Monito
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p.1 #2 · 16-35L II DOF observations


Daan B wrote:
Another thing that is really weird is that 28mm the 16-35L II has really sharp extreme corners and center, but the area in focus that lies in-between is relatively soft. So, the extreme corners are sharper than the corners It almost looks like at 28mm there is so much field curvature that the area in focus has the shape of half a circle: sharp in the center and then dropping off to the extreme corners very rapidly.


The 16-35 L Mark II is covered by Canon DPP DLO (Digital Lens Optimizer) so it can be corrected easily.

The MTF diagrams have dips that then rise closer to the corners before dropping off like almost all lenses do since the corners are near the edge of the image circle. The "Tele" end, which would be around 28 mm on that lens, has three curves that rise at the corners.






Aug 03, 2012 at 01:10 PM
dsjtecserv
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p.1 #3 · 16-35L II DOF observations


Your impression of different depth of field extent and distribution is probably a result of differences in the characteristics of the image and the lenses, such as the noted differences in edge sharpness, rather than an actual DoF difference. Depth of field is a function of the focal length, aperture, etc., and is independent of differences in lens design, so there shouldn't be any actual difference in the DoF results you see.

Dave



Aug 03, 2012 at 02:02 PM
Daan B
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p.1 #4 · 16-35L II DOF observations


dsjtecserv wrote:
Your impression of different depth of field extent and distribution is probably a result of differences in the characteristics of the image and the lenses, such as the noted differences in edge sharpness, rather than an actual DoF difference. Depth of field is a function of the focal length, aperture, etc., and is independent of differences in lens design, so there shouldn't be any actual difference in the DoF results you see.


Well, there is a difference for sure. The 16-35L II is sharp across the frame (left, right and center), the area in (sharp) focus just doesn't reach as deep as the other lenses do at comparable fl's and apertures. The lenses where tested on a fixed camera/tripod position, so the result should be the same like you have said. But they aren't.



Aug 03, 2012 at 02:46 PM
form
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p.1 #5 · 16-35L II DOF observations


That sounds extremely odd since MY 16-35 II behaves like an ultrawide, with crappy corners until at least f/5.6-f/8 and deep DoF @16mm at even the widest aperture.


Aug 03, 2012 at 03:07 PM
dsjtecserv
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p.1 #6 · 16-35L II DOF observations


Daan, for the three lenses you listed, the only focal length they have in common is 35 mm. Is that the focal length at which you did the comparison? For any other focal length, the zooms would obviously have different depth of field from the 35 prime.

Also, the comparison can only be made if all lenses are focused at exactly the same distance, preferably in the center of the frame. I agree that field curvature could create differences for surfaces away from the center, but that should not be significant unless the focus distance is very short.

Dave



Aug 03, 2012 at 03:26 PM
Daan B
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p.1 #7 · 16-35L II DOF observations


form wrote:
That sounds extremely odd since MY 16-35 II behaves like an ultrawide, with crappy corners until at least f/5.6-f/8 and deep DoF @16mm at even the widest aperture.


Mine does too, except for 28mm.



Aug 03, 2012 at 04:30 PM
Daan B
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p.1 #8 · 16-35L II DOF observations


dsjtecserv wrote:
Daan, for the three lenses you listed, the only focal length they have in common is 35 mm. Is that the focal length at which you did the comparison? For any other focal length, the zooms would obviously have different depth of field from the 35 prime.


There is also 24mm. I did the comparison at 24mm and 35mm for the 16-35 and 24-105. The 35L was tested only at 35mm obviously. But it showed the same performance as the 24-105L @ 35mm. All were tested against each other using the same fixed position and at comparable focal lengths and apertures. But the 16-35L II actually had a tighter framing than the 24-105L @ comparable fl's.

Also, the comparison can only be made if all lenses are focused at exactly the same distance, preferably in the center of the frame.

They were.

I agree that field curvature could create differences for surfaces away from the center, but that should not be significant unless the focus distance is very short.

Focus distance was about 5 to 7 meters (approx). I don't have an explanation either. The MTF charts that Monito posted may have something to do with it.



Aug 03, 2012 at 04:33 PM
Daan B
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p.1 #9 · 16-35L II DOF observations


Let me see if I can post a sample later on.


Aug 03, 2012 at 04:37 PM
jerrykur
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p.1 #10 · 16-35L II DOF observations


I am not surprised at this observation. Each zoom lens is a set of design choices made to get the lens perform well across it's entire focal length range. Pushing a lens to it limits, say <= 28 mm on the 24-105 is where I would expect any design compromises to be most obvious.




Aug 03, 2012 at 04:50 PM
 

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Daan B
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p.1 #11 · 16-35L II DOF observations


On the reduced sharpness in the area between the center and extreme corner I would like you to see the following example.

Full picture, 16-35L II on 5D2 @ 25mm, f/5.6 (RAW conversion in LR 3.6 @ default values)






100% crop center - notice how sharp the tree in the background is. This tree is farther away from the center than the buildings to the left and right. Focus is on the wooden fence.






100% crop upper left corner - notice that the extreme edge of the frame is sharpest (roof tiles).






100% crop upper right corner - notice how the extreme edge of the frame is sharpest (brick building)






What to make of this? At about f/11 sharpness becomes more evenly distributed.

BTW I took the same shot with the 24-105L and it showed the extreme corners softer, but both the whole roof and brick buildings are sharp. More what I would expect from a WA point of view.



Aug 03, 2012 at 09:02 PM
Gunzorro
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p.1 #12 · 16-35L II DOF observations


Daan -- I see what you are saying. Mine doesn't behave that way. I have good sharpness across the great center of the image, but even at f/8, my corners are soft. Mine is much better after sending to Canon for adjustment. I'd rather have soft corners/edges than an unsharp band 2/3 out from center.

I say, send it in with a couple prints or USB stick of your problems.

Or take it back and try another version.



Aug 03, 2012 at 10:00 PM
trumpet_guy
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p.1 #13 · 16-35L II DOF observations


I suspect there is some non-flatness of field in this case, Daan. Try varying the focus just a tiny bit and you might find that the locations of the sharp and soft sections reverse.


Aug 04, 2012 at 04:08 AM
Cphoto1954
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p.1 #14 · 16-35L II DOF observations


There are good and bad versions of this lens. I had an excellent copy that I recently sold but it took a few to get there. So if you can return it do so and try another one.


Aug 04, 2012 at 05:31 AM
Daan B
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p.1 #15 · 16-35L II DOF observations


Gunzorro wrote:
Daan -- I see what you are saying. Mine doesn't behave that way. I have good sharpness across the great center of the image, but even at f/8, my corners are soft. Mine is much better after sending to Canon for adjustment. I'd rather have soft corners/edges than an unsharp band 2/3 out from center.

I say, send it in with a couple prints or USB stick of your problems.

Or take it back and try another version.


Too late to take it back. I'll run this by CPS. See what they have to say. IMO They should swap it for another copy that works like it should work.



Aug 04, 2012 at 06:08 AM
Daan B
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p.1 #16 · 16-35L II DOF observations


trumpet_guy wrote:
I suspect there is some non-flatness of field in this case, Daan. Try varying the focus just a tiny bit and you might find that the locations of the sharp and soft sections reverse.


I have other shots under different circumstances. Even flat shots of a brick wall. But the issue remains.



Aug 04, 2012 at 06:09 AM
indiawilds
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p.1 #17 · 16-35L II DOF observations


I am satisfied with the 16-35 f2.8L II lens. Didn't notice the problems you are facing. The 24-105 is a different lens all together. When I am filming barebones handheld, the 24-105 I pick up the 24-105 for its IS.


Aug 04, 2012 at 11:02 AM
Monito
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p.1 #18 · 16-35L II DOF observations


Welcome to FM, indiawilds.



Aug 04, 2012 at 11:48 AM
indiawilds
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p.1 #19 · 16-35L II DOF observations


Monito,
Thanks for the welcome.



Aug 04, 2012 at 03:38 PM
Daan B
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p.1 #20 · 16-35L II DOF observations


trumpet_guy wrote:
I suspect there is some non-flatness of field in this case, Daan. Try varying the focus just a tiny bit and you might find that the locations of the sharp and soft sections reverse.


On second thought you might be right. I checked the focus plane on several images and it seems the plane bends towards the corners from the center in half an oval-like shape. Or even some kind of mustache-like shape, where the extreme corners are (almost) as sharp as the center. It is definitely not flat! Would you consider this amount of field curvature normal for this type of lens? Or maybe there is sample variation among lenses, and I got one that has more field curvature than other copies? Or maybe it points towards some kind of defect?



Aug 04, 2012 at 08:55 PM
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