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Archive 2010 · Nikon 14-24/2.8 - some questions (full res images!)

  
 
Bobu
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p.1 #1 · p.1 #1 · Nikon 14-24/2.8 - some questions (full res images!)


I have some questions regarding the Nikon 2.8/14-24mm lens. I used this lens on a Canon 5D II for about one year (with 16-9-adapter).
Most of the pictures are very good: great contrast and very good sharpness, even in the extreme corners. But once in while I get a picture where some corners or some edges are really soft.

This happens mostly at 14mm focal length, with apertures between 2.8 and 5.6 and a focus point at close distances (between2 and 5 meters). Strange is, that only some corners appear soft while others (and the center) are still very sharp. The camera was always mounted on a tripod with mirror lockup and live-view-focusing.
Here are two full-res examples (probably at f/5.6). On the first pictures you can clearly see, that the upper left and upper right corners/edges are soft, while the rest of the image is pretty sharp. On the second image you can see that the right edge is soft, everything else looks sharp.
When I take pictures of a flat wall I don't see any differences between the corners and everything looks pretty good at f/5.6.

Is this strange behavior typical for this lens? Any ideas what's the reason for this is?

By the way Nikon tested this lens twice with the result that everything is perfectly within the spec.

Boris

#1:
http://farm5.static.flickr.com/4095/4793542517_4bde3322a3_o.jpg

#2:
http://farm5.static.flickr.com/4143/4793475165_c60f850311_o.jpg



Jul 14, 2010 at 01:39 PM
wayne seltzer
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p.1 #2 · p.1 #2 · Nikon 14-24/2.8 - some questions (full res images!)


Looks/sounds like the result of field curvature. I can try recreating this scenario with my copy later today after work if get time. I usually shoot landscapes at f8, have Mark's original adapter, and usually focus father away closer to infinity since the DOF is so large with the lens, especially at 14mm.
Try taking shots at f5.6 but keep moving the focus point from near to far and see the difference of sharpness in the borders and corners. You could use Liveview to focus and see when the borders/corners become sharp.



Jul 14, 2010 at 06:00 PM
Andi Dietrich
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p.1 #3 · p.1 #3 · Nikon 14-24/2.8 - some questions (full res images!)


this looks like a DOF issue, stop down to f11 and use a higher ISO setting, like 1600.


Jul 14, 2010 at 06:00 PM
Bobu
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p.1 #4 · p.1 #4 · Nikon 14-24/2.8 - some questions (full res images!)


It seems, that the problem has something to do with (limited) DOF.
But all objects at close distances (even in the lower corners) are sharp. At the same time all objects at middle and far distances in the center are sharp. Only objects at middle (to far) distances at the edge of the frame are soft.
It could be the result of a strong field curvature of this lens, but then this should also be clearly visible in brickwall shots.

Wayne, it would be great if you could try to recreate this scenario with your lens.

Thanks,

Boris



Jul 14, 2010 at 11:57 PM
edwardkaraa
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p.1 #5 · p.1 #5 · Nikon 14-24/2.8 - some questions (full res images!)


Definitely DOF issue. Nothing to worry about imo. Ironically I think this is accentuated by this lens' flat field curvature. Lenses with pronounced curvature like my Zeiss 16-35 can sometimes give you unbelievable depth that cannot be obtained by simply stopping down. They perform poorly in brick wall tests though.


Jul 15, 2010 at 12:08 AM
Bobu
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p.1 #6 · p.1 #6 · Nikon 14-24/2.8 - some questions (full res images!)


edwardkaraa wrote:
Definitely DOF issue. Nothing to worry about imo. Ironically I think this is accentuated by this lens' flat field curvature. Lenses with pronounced curvature like my Zeiss 16-35 can sometimes give you unbelievable depth that cannot be obtained by simply stopping down. They perform poorly in brick wall tests though.


Thanks Edward, but i still don't understand what's going on. If the lens has a flat field curvature shouldn't be the center and edges at middle distances have the same level of sharpness?
I would rather sucpect a strong field curvature, where the edges are focused to a closer distance than the center.

Boris



Jul 15, 2010 at 12:22 AM
edwardkaraa
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p.1 #7 · p.1 #7 · Nikon 14-24/2.8 - some questions (full res images!)


I withdraw my earlier comments. Having inspected the photos thouroughly (they took a long time to download and I wasn't patient enough the first time), I can see the following:

In both images Center is sharp both at near and far distances. As we move to the edges the focus is shifting to the foreground, rendering longer distances unsharp.

Typical workings of field curvature. Usually the field curvature is the strongest at the widest zoom setting and gets better as you zoom in. That is why most reviewers found this zoom stellar as compared to the Zeiss 21/2.8 as at this FL the curvature should be practically inexistent.

Interesting to see the field curvature being in a reversed U shape. The Zeiss 16-35 has the exact opposite as it is U shaped. In your photos the far away borders would have been sharp and the foreground blurred.



Jul 15, 2010 at 03:03 AM
Bobu
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p.1 #8 · p.1 #8 · Nikon 14-24/2.8 - some questions (full res images!)


edwardkaraa wrote:
I withdraw my earlier comments. Having inspected the photos thouroughly (they took a long time to download and I wasn't patient enough the first time), I can see the following:

In both images Center is sharp both at near and far distances. As we move to the edges the focus is shifting to the foreground, rendering longer distances unsharp.

Typical workings of field curvature. Usually the field curvature is the strongest at the widest zoom setting and gets better as you zoom in. That is why most reviewers found this zoom stellar as compared to the Zeiss 21/2.8 as at this FL
...Show more

Thanks Edward, that makes sense. But it also makes this lens (@14mm) at bit difficult to use for me, at least under field conditions where you often don't have enough time to thoroughly check for corner sharpness with liveview (for example due to quickly changing light conditions or heavy rain like in these two pictures).

Boris



Jul 15, 2010 at 11:54 AM
wayne seltzer
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p.1 #9 · p.1 #9 · Nikon 14-24/2.8 - some questions (full res images!)


Edward, glad you agree with me now.

Boris,

I didn't get a chance to try and recreate this with my copy last night, but maybe tonight.
I have shot landscapes with this lens successfully at 14mm at f8 and have not seen this problem before.
I think it may have to do with your focus pt. being too close. Trying taking shots with the focus pt. near or at infinity pt. and see what you get. It should be much better than this with good sharpness from front to back and across the frame. Once you figure out what focus distance range is the optimum for this type of shot, then you just remember it for those times when you don't want to check via liveview.



Jul 15, 2010 at 12:51 PM
edwardkaraa
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p.1 #10 · p.1 #10 · Nikon 14-24/2.8 - some questions (full res images!)


Completely agreed with Wayne. Focusing at infinity should help improve the edges. Interesting issue nonetheless.


Jul 15, 2010 at 02:40 PM
Specularist
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p.1 #11 · p.1 #11 · Nikon 14-24/2.8 - some questions (full res images!)


There may be field curvature and depth-of-field issues here, but there's also another significant factor: subject movement. The vegetation in both photos is clearly moving in the wind. I'd therefore be cautious about using these samples to draw conclusions about the lens.


Jul 15, 2010 at 03:34 PM
wayne seltzer
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p.1 #12 · p.1 #12 · Nikon 14-24/2.8 - some questions (full res images!)


I was also thinking the same thing about the trees moving on the left side in the first picture but in the 2nd photo the flowers in the middle foreground are clearly sharper than the ones in the lower left and right corners and sides and they would be probably be moving the same amount if there was wind movement so I discounted that idea.


Jul 15, 2010 at 04:11 PM
wayne seltzer
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p.1 #13 · p.1 #13 · Nikon 14-24/2.8 - some questions (full res images!)


BTW, I should send my camera and copy of the 14-24G to Edward as he has the official field curvature testing sofa.


Jul 15, 2010 at 04:14 PM
Bobu
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p.1 #14 · p.1 #14 · Nikon 14-24/2.8 - some questions (full res images!)


In will be offline until monday. So if there are any further ideas regarding field-curvature or some test-images from Wayne I will answer on monday.

By the way, I'm pretty sure, that subject movement is not a significant factor in these images. Just look at the trees in the center.

Boris



Jul 16, 2010 at 06:59 AM





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