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Archive 2013 · Lens test and field curvature
  
 
kevindar
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p.1 #1 · p.1 #1 · Lens test and field curvature


I am testing a new lens that I purchased, an on one side of the frame (right side) it appears to be focusing much closer, or at least have the close objects in sharp focus, and far objects not sharp. even at f11, its not quite as sharp as it should be? is it a decentered element?
I shot this with the tamy 24-70 at 24, f4, and canon 24-105. the focus point is the house across the street. I focused where the rocks passed fire hydrant are.
scene for reference





Tamy on top, Canon on bottom
Extreme left (street sign)













now extreme right, seems to be in close enough focus plane, but tamy struggles except the close up tree is very sharp











and finally, R foreground. (bottom r corner), where tamy does very well.












here is the softer right side at f11, 24 mm











the problem continues at 28 and 35 mm, and gone at 50 and 70.
what is the problem? should I send it in for an exchange? thanks for looking and any thoughts.








Jul 10, 2013 at 06:51 AM
johnctharp
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p.1 #2 · p.1 #2 · Lens test and field curvature


I can't really help you answer the question, as much as I'm just curious as to what other people have to say.

From what I can see, the Tamy is sharper and has much better LoCA control, but it almost looks like it is focusing two images very close together on the sensor; like one is ever so slightly misaligned with the other, in the backgrounds. It reminds me of what a '3D' movie looks like without 3D glasses on, really, just not as extreme.



Jul 10, 2013 at 10:05 PM
kevindar
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p.1 #3 · p.1 #3 · Lens test and field curvature


the tamron is definitely sharp, except on the right side, for far object up until close to 50. I think there is a decentering issue, and I will probably need to replace the lens.


Jul 10, 2013 at 11:11 PM
johnctharp
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p.1 #4 · p.1 #4 · Lens test and field curvature


I definitely would, now that I've looked at your example shots again. Even with it's softer image and LoCA, the 24-105L seems to have much better bokeh rendering. And realistically, I wouldn't want to use an image like that; I wouldn't accept image quality like that from any lens, let alone a new, expensive workhorse zoom .

Go try as many as you need to and get yourself a good one. I've seen the sample images in many reviews, so I know that there are good ones out there! Don't give up .



Jul 12, 2013 at 05:24 PM
skibum5
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p.1 #5 · p.1 #5 · Lens test and field curvature


Sadly it really seems to be something tricky to avoid with the wider zooms. Every single 24-70 II I looked at see,Ed to place the region within the DOF differently across the frame!


Jul 12, 2013 at 08:45 PM
David Baldwin
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p.1 #6 · p.1 #6 · Lens test and field curvature


Just a brief observation, for what its worth.

I've had lenses which as part of their necessary design compromises do have field curvature. But what I would say is that in a properly assembled lens of that type the corners might be less than perfectly sharp but CRUCIALLY all four corners would display exactly the same amount of softness. If the corners vary that is an assembly issue, not a field curvature one as it shows the lens is not assembled symmetrically - assuming of course the lens settings are not changed between the four shots and that you move the camera (on a tripod) so that the corner of the frame comes to rest on the same object for each test exposure (if you see what I mean).



Jul 13, 2013 at 11:19 AM
 

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kevindar
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p.1 #7 · p.1 #7 · Lens test and field curvature


David, you are exactly correct. My 16-35II definitely has a field curvature, with a closer focusing near the edges and corners. I makes the foreground a little sharper. but its uniformely so. this lens seems to curve in only on the right side. I got a second copy. i will compare them and post.


Jul 13, 2013 at 03:05 PM
kevindar
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p.1 #8 · p.1 #8 · Lens test and field curvature


So I am on my second copy now. I did a brick wall test, and at 24, neither of them are as sharp as my 24-105 in the far corners, but both are better in the near corner. the second copy is actually even worse in the R side and right upper corner at 24, slightly better at 35. Its funny b/c I think all the tests done by the digital picture, dxo, dpreview etc, check the lens in studio at close focus distance, where the sharpness is much better in the corners. I am starting to think this is certainly not a great landscape lens. my 24-105 seems to perform better at far objects (more than 20 feet) at all focal lengths at f5.6 on, sometimes f4 on. on the flip side, for people photography, the lens seems to perform very well, within 10-15 feet, with excellent sharpness.


Jul 14, 2013 at 12:18 AM
skibum5
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p.1 #9 · p.1 #9 · Lens test and field curvature


kevindar wrote:
So I am on my second copy now. I did a brick wall test, and at 24, neither of them are as sharp as my 24-105 in the far corners, but both are better in the near corner. the second copy is actually even worse in the R side and right upper corner at 24, slightly better at 35. Its funny b/c I think all the tests done by the digital picture, dxo, dpreview etc, check the lens in studio at close focus distance, where the sharpness is much better in the corners. I am starting to think this is
...Show more

You could try placing focus a bit deeper or somewhat shallower than with the 24-105 and see how it works then for distant scenes. I'm surprised to hear the Tamron 24-70 VC might be worse thant he 24-105 since I had a nasty time getting 24-105 to fit real world distant, complex landscape scenes (my tamron 28-75 2.8 actually behaved better), but it could be and if so then especially glad I got the 24-70 II (although I am a bit troubled that ALL copies I tried placed DOF differently compared to each other copy, often noticeably so copy to copy to copy; my current copy is generally superb but I feel it probably slightly pushes back the plane of focus at the bottom left and brings it slightly forward top right, but otherwise excellent (and for scenes not having very deep upper right or near lower left it is 100% crisp corner to corner on 5D3 at 24mm) and the f/2.8 center frame performance is outstanding, best of all the copies, already noticeably sharper 70mm f/2.8 center frame than the 70-200 f/4 IS or even 70-300L IS are at 70mm f/4).



Jul 14, 2013 at 03:23 AM
kevindar
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p.1 #10 · p.1 #10 · Lens test and field curvature


thanks skibum for your suggestion. I actually compared the all three extensively agian (the two copies of 24-70, and the 24-105). My first copy is clearly decentered. compared to the second copy, it is softer on the right side at every focal length and every F stop. then I compared the better copy to 24-105, and even the second copy is slightly decentered, again doing slightly worse on the right side at 24 and 35, even stopped down, same or better on the left. at wider focal lengths it does better on the foreground, buy a good margin actually. also it has better contrast. a crop of top left and top right are very different on the tamron. here is the example.
this is the better copy of tamron. 24 F4. I intentionally slightly tilted the camera up. should not make a difference at f4 24mm.






here are the 4 corners of tamron you can see how poor the right upper side is, compared to left





here are the canon. I would say very uniform.






Tamron does better in 3/4 corners, but a lot worse on the top right. its not just even the corner, the sides never quite get as sharp even at f8.



Jul 14, 2013 at 03:56 AM
timpdx
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p.1 #11 · p.1 #11 · Lens test and field curvature


The second set of pics of the warehouse wall really shows the problem you are having. (god knows there is a ton of that warehouse pebble texture crap in SoCal). I would be sending that Tammy back.


Jul 14, 2013 at 04:34 AM





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