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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 03 Aug 2012 (Friday) 16:43
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16-35L II soft between center and extreme corners

 
Daan37
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Aug 03, 2012 16:43 |  #1

I noticed reduced sharpness in the area between the center and extreme corner of my 16-35L II.

Full picture, 16-35L II on 5D2 @ 25mm, f/5.6 (RAW conversion in LR 3.6 @ default values)
http://farm9.staticfli​ckr.com …06512486_aeb6dc​d213_b.jpg (external link)

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.
http://farm8.staticfli​ckr.com …06512832_153b38​51ba_b.jpg (external link)

100% crop upper left corner - notice that the extreme edge of the frame is sharpest (roof tiles).
http://farm9.staticfli​ckr.com …06513268_d6f250​8c21_b.jpg (external link)

100% crop upper right corner - notice how the extreme edge of the frame is sharpest (brick building)
http://farm8.staticfli​ckr.com …06513694_db0f81​48e7_b.jpg (external link)

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.


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Saint728
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Aug 03, 2012 19:18 |  #2

That is all you will get from the corners with the Canon 16-35mm f/2.8L II lens. The Canon 17-40 has the same or slightly better corners at f/8. I had both but sold the 16-35 because I never shot it at f/2.8. If you want something better in the corners, have a look at the Zeiss Distagon T* 21mm f/2.8 ZE.

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Cheers, Patrick


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Aug 04, 2012 00:32 as a reply to  @ Saint728's post |  #3

Don't know, but with the varying distances to the objects, I would guess DOF. Everything you pointed out being less sharp is further away. Even though you tried with the 24-105, perhaps the focus point was not in exactly the same place. I have seen slight differences in DOF between lenses away from the center (I guess due to trying to correct for distortion, CA ect..).

So the only way to really confirm this would be to shoot something flat.


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Daan37
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Aug 04, 2012 01:11 |  #4

Saint728 wrote in post #14811207 (external link)
That is all you will get from the corners with the Canon 16-35mm f/2.8L II lens. The Canon 17-40 has the same or slightly better corners at f/8. I had both but sold the 16-35 because I never shot it at f/2.8. If you want something better in the corners, have a look at the Zeiss Distagon T* 21mm f/2.8 ZE.

Take Care,
Cheers, Patrick

The (extreme) corners aren't the issue... they are actually sharper than what is between them and the center. And that shouldn't be the case IMO.


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Daan37
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Aug 04, 2012 01:14 |  #5

ejenner wrote in post #14812241 (external link)
Don't know, but with the varying distances to the objects, I would guess DOF. Everything you pointed out being less sharp is further away. Even though you tried with the 24-105, perhaps the focus point was not in exactly the same place. I have seen slight differences in DOF between lenses away from the center (I guess due to trying to correct for distortion, CA ect..).

So the only way to really confirm this would be to shoot something flat.

The tree in the background is farther away from the center than the buildings to the side. If it were DOF (what I assumed at first too) the tree should have been soft too.

On the placement of the focal point... the 24-105L was tested against the 16-35L II from exact the same (fixed) tripod position. Focus on the center was also exactly the same.

If I shoot something flat like a brick wall, the softness half way the frame is there too.

I think I'll sent it in :(


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rick_reno
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Aug 04, 2012 11:08 |  #6

i'd send it in, something sounds out of whack in it.




  
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Wilt
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Aug 04, 2012 11:39 |  #7

Before you jump to any conclusions, set up your camera on a tripod in front of a large flat wall or fence with the camera parallel to that flat surface. Then take photos and compare sharpness at different points in the frame. But keep in mind, while evaluating results, that

  • the focus plane is sometimes NOT a flat plane because some lenses have field curvature
  • it is normal for there to be reduced lens resolution at the Edge of frame, compared to Center of frame


I shot this photo to prove to someone that many lenses indeed have flat plane of focus, not curved fields.
IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/IMG_6883.jpg

And you can see that the grasscloth detail on the wall is uniformly sharp.

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Daan37
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Aug 04, 2012 13:43 |  #8

Wilt, I did shoot a brick wall (just like you shot your wall) and the sharpness isn't evenly distributed.


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Wilt
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Aug 04, 2012 13:58 |  #9

Daan37 wrote in post #14813908 (external link)
Wilt, I did shoot a brick wall (just like you shot your wall) and the sharpness isn't evenly distributed.

Can you post that on POTN, so we can see what you are experiencing?


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Lowner
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Aug 04, 2012 14:42 |  #10

Wilt wrote in post #14813506 (external link)
Before you jump to any conclusions, set up your camera on a tripod in front of a large flat wall or fence with the camera parallel to that flat surface. Then take photos and compare sharpness at different points in the frame. But keep in mind, while evaluating results, that
  • the focus plane is sometimes NOT a flat plane because some lenses have field curvature
  • it is normal for there to be reduced lens resolution at the Edge of frame, compared to Center of frame

I shot this photo to prove to someone that many lenses indeed have flat plane of focus, not curved fields.
QUOTED IMAGE

And you can see that the grasscloth detail on the wall is uniformly sharp.

I see that the LHS is not quite sharp while the RHS is.


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Wilt
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Aug 04, 2012 15:31 |  #11

Lowner wrote in post #14814059 (external link)
I see that the LHS is not quite sharp while the RHS is.

That could well be. When I took the shot rather hurriedly, I was more after the illustration of 'flat plane of focus' rather than 'curved field of focus' (the debate within that thread), and I didn't really take the time to ensure parallelism between the wall and the sensor.
In using the same shot again, in this thread, I was illustrating the principle of flat wall as a target but not necessarily perfect execution! :)


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Daan37
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Aug 04, 2012 15:52 |  #12

After looking more carefully at some images it might indeed be a rather heavy field curvature at work here. It looks like the focus plane bends towards the corners from the center in the shape of a cut through oval. Definitely not flat. I wonder if this is normal for this type of lens. Maybe there is sample variation between lenses in the amount field curvature? I am not sure, but it also seems that at certain focal lengths the field is curved more in a mustache-like shape.

Unfortunately I can't post very big. In order to see the focus plane clearly I have to zoom in quite a bit (100% crops).


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Wilt
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Aug 04, 2012 16:05 |  #13

Daan37 wrote in post #14814261 (external link)
After looking more carefully at some images it might indeed be a rather heavy field curvature at work here. It looks like the focus plane bends towards the corners from the center in the shape of a cut through oval. Definitely not flat. I wonder if this is normal for this type of lens. Maybe there is sample variation between lenses in the amount field curvature? I am not sure, but it also seems that at certain focal lengths the field is curved more in a mustache-like shape.

Unfortunately I can't post very big. In order to see the focus plane clearly I have to zoom in quite a bit (100% crops).

photozone.de has noted curvature of field in the earlier Tamron 17-50 (not VC version) but it does not comment on that being an issue in the 16-35mm.


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jdizzle
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Aug 04, 2012 18:23 |  #14

I always thought the 16-35 was impressive until I picked up the Zeiss 21, 17 TS and 24 TS II. ;)




  
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Lowner
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Aug 05, 2012 02:50 |  #15

Daan37 wrote in post #14814261 (external link)
After looking more carefully at some images it might indeed be a rather heavy field curvature at work here. It looks like the focus plane bends towards the corners from the center in the shape of a cut through oval. Definitely not flat. I wonder if this is normal for this type of lens. Maybe there is sample variation between lenses in the amount field curvature? I am not sure, but it also seems that at certain focal lengths the field is curved more in a mustache-like shape.

Unfortunately I can't post very big. In order to see the focus plane clearly I have to zoom in quite a bit (100% crops).

A totally flat focal plane is not possible, it exists as a theoretical target only. Given that naturally the plane will be a sphere centred on the camera, any flattening will be by introducing more glass, more distortion. As technology gets better, so the flat field gets better, but it presumably will never actually get there.


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16-35L II soft between center and extreme corners
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