p.1 #1What do you think about this centering test?
Jannik Peters reviewed the Zeiss Loxia 2.8/21 on my blog but he has a decentered copy. When he spoke with a Zeiss representative about the issue he was asked how he tested his lens for de-centering and he answered that he used the Gletscherburch method. Apparently the Zeiss representative ridiculed the method and questioned that Jannik's copy of the Loxia 21 was actually decentered.
The site is in German so a short translation from me:
1) look for an object which has fine details and is at least 20m away, optimally a few hundred meters
2) put the camera on a tripod activate mirror lockup and selftimer or remaote release
3) put the object in the center of the image and focus on it. From now on deactivate AF and do not touch the focusing ring.
4) if your lens isn't sharp in the corners from it's widest aperture stop down to an approriate aperture
5) fix exposure
6) now put the object from step 1 in each of the four corners and take four pictures. The sample image in the link illustrates this step well.
7) when you compare the images the object should show the same sharpness in each of them
Now my question is what you think of the method and if you see any reason to question it or know a better method. To me it is a good method because it eliminates any alignment errors from the user which can easily happen if you use your cupboard for testing. I also wouldn't know a better method so both Jannik and I were a bit flabbergasted by the reaction from Zeiss.
p.1 #2What do you think about this centering test?
A few years ago I bought a CV 15mm f4.5 LTM and a CV 21mm f4 LTM at a reasonable price. However, both lenses were heavily decentered. I've disassembled and reassembled them a lot of times until they were to my liking.
In order to test them I've used exactly the same procedure you outlined above. The procedure worked very well for me.
p.1 #3What do you think about this centering test?
For long lens, I can see the merit of this testing. For WA and SWA, I feel this method might be difficult to excude, given it also introduce perspective distortion. especially with lens has FC and coma, sharpness judgement can be difficult and prone to human error. This will introduce complication unneeded IMO.
To have a infinity horizon diagonally cross the frame and Simple focus at center infinity to inspect corner evenness is more robust approach to me.
Phillip Reeve wrote:
Jannik Peters reviewed the Zeiss Loxia 2.8/21 on my blog but he has a decentered copy. When he spoke with a Zeiss representative about the issue he was asked how he tested his lens for de-centering and he answered that he used the Gletscherburch method. Apparently the Zeiss representative ridiculed the method and questioned that Jannik's copy of the Loxia 21 was actually decentered.
The site is in German so a short translation from me:
1) look for an object which has fine details and is at least 20m away, optimally a few hundred meters
2) put the camera on a tripod activate mirror lockup and selftimer or remaote release
3) put the object in the center of the image and focus on it. From now on deactivate AF and do not touch the focusing ring.
4) if your lens isn't sharp in the corners from it's widest aperture stop down to an approriate aperture
5) fix exposure
6) now put the object from step 1 in each of the four corners and take four pictures. The sample image in the link illustrates this step well.
7) when you compare the images the object should show the same sharpness in each of them
Now my question is what you think of the method and if you see any reason to question it or know a better method. To me it is a good method because it eliminates any alignment errors from the user which can easily happen if you use your cupboard for testing. I also wouldn't know a better method so both Jannik and I were a bit flabbergasted by the reaction from Zeiss....Show more →
p.1 #4What do you think about this centering test?
I did not know that someone has actually put a name to this method that I have been using for over 20 years to test a lens for de-centering but glad that I am not the only one.
I had a couple of copies of a Voigtlander 21/4 lens that were de-centered. The third copy was spot on when I supplied the test shots the shop did not want to know either and questioned the method used but could not disprove my findings or come up with another method.
The test as far as I am concerned works perfectly as long as you focus at something that is at infinity. Perspective distortion will be evident with wide angle lenses but a trained eye will be able to distinguish that immediately particularly if images of all four corners are taken.
Because the image is taken at infinity this method is far more reliable than taking an image of a wall or test chart as this will have to be aligned perfectly which is almost impossible to do in a non professional setting.
p.1 #5What do you think about this centering test?
This test works very well, i do it on all new lens purchases.
But I would recommend not to stop the lens down, as suggested in 4)
Decentering is seen best when shot wide open.
p.1 #6What do you think about this centering test?
You can also use a flat surface with a geometrically symmetric pattern. That makes it easy to line up the lens perpendicular to the surface. Since it allows you to shoot at much shorter distance, any decentering will be more clearly visible because of shorter DOF.
p.1 #8What do you think about this centering test?
If the method is to take a photo of an infinite object at best center focus and compare the resolution in the 4 corners it is fine. If it is more complicated I would need a clear explanation of what is done to tell if you if it has validity.
I think it is quite pompous to name such a test after yourself, however.
p.1 #9What do you think about this centering test?
Brandon Dube wrote:
If the method is to take a photo of an infinite object at best center focus and compare the resolution in the 4 corners it is fine. If it is more complicated I would need a clear explanation of what is done to tell if you if it has validity.
I think it is quite pompous to name such a test after yourself, however.
thanks for chiming in.
It is referred to as the Gletscherbruch Test in German forums because that site offers a clear and rather foolproof explanation of the method. So the name was attributed by others not by the site itself. But your summary is to the point.
p.1 #10What do you think about this centering test?
zhangyue wrote:
For long lens, I can see the merit of this testing. For WA and SWA, I feel this method might be difficult to excude, given it also introduce perspective distortion. especially with lens has FC and coma, sharpness judgement can be difficult and prone to human error. This will introduce complication unneeded IMO.
To have a infinity horizon diagonally cross the frame and Simple focus at center infinity to inspect corner evenness is more robust approach to me.
Phillip Reeve wroteJannik Peters reviewed the Zeiss Loxia 2.8/21 on my blog but he has a decentered copy. When he spoke with a Zeiss representative about the issue he was asked how he tested his lens for de-centering and he answered that he used the Gletscherburch method. Apparently the Zeiss representative ridiculed the method and questioned that Jannik's copy of the Loxia 21 was actually decentered.
The site is in German so a short translation from me:
1) look for an object which has fine details and is at least 20m away, optimally a few hundred meters
2) put the camera on a tripod activate mirror lockup and selftimer or remaote release
3) put the object in the center of the image and focus on it. From now on deactivate AF and do not touch the focusing ring.
4) if your lens isn't sharp in the corners from it's widest aperture stop down to an approriate aperture
5) fix exposure
6) now put the object from step 1 in each of the four corners and take four pictures. The sample image in the link illustrates this step well.
7) when you compare the images the object should show the same sharpness in each of them
Now my question is what you think of the method and if you see any reason to question it or know a better method. To me it is a good method because it eliminates any alignment errors from the user which can easily happen if you use your cupboard for testing. I also wouldn't know a better method so both Jannik and I were a bit flabbergasted by the reaction from Zeiss.
The critical point is of course in determining how much of a difference between the corners is too much. Distortion, field curvature and coma are of course affecting and wide angle to varying degrees but I don't really see why they should be a problem, they should affect each corner the same.
I think the Lens Rentals method is a good double check, I think using multiple methods to determine if a lens has de-centered elements is far better than to rely on just one.
Note: Yes I know the closer to infinity you set focus the less of an issue this becomes due to increased DOF.
p.1 #14What do you think about this centering test?
It should be off by the same amount, and yes, closer to infinity gives you more DOF vs 5m.
It's not ideal, but it's the best & cheapest method we all have at our disposal.
It's the only thing I can see why the Zeiss techs don't like that method.
p.1 #15What do you think about this centering test?
I read the test description in the original link - sounds good to me! It is also expressed in there that the decentering should be visible even when the aperture is stopped down a bit. This should balance out any potential slight error from plane of focus shift as expressed above.
p.1 #16What do you think about this centering test?
Phillip Reeve wrote: zhangyue wroteFor long lens, I can see the merit of this testing. For WA and SWA, I feel this method might be difficult to excude, given it also introduce perspective distortion. especially with lens has FC and coma, sharpness judgement can be difficult and prone to human error. This will introduce complication unneeded IMO.
To have a infinity horizon diagonally cross the frame and Simple focus at center infinity to inspect corner evenness is more robust approach to me.
Phillip Reeve wroteJannik Peters reviewed the Zeiss Loxia 2.8/21 on my blog but he has a decentered copy. When he spoke with a Zeiss representative about the issue he was asked how he tested his lens for de-centering and he answered that he used the Gletscherburch method. Apparently the Zeiss representative ridiculed the method and questioned that Jannik's copy of the Loxia 21 was actually decentered.
The site is in German so a short translation from me:
1) look for an object which has fine details and is at least 20m away, optimally a few hundred meters
2) put the camera on a tripod activate mirror lockup and selftimer or remaote release
3) put the object in the center of the image and focus on it. From now on deactivate AF and do not touch the focusing ring.
4) if your lens isn't sharp in the corners from it's widest aperture stop down to an approriate aperture
5) fix exposure
6) now put the object from step 1 in each of the four corners and take four pictures. The sample image in the link illustrates this step well.
7) when you compare the images the object should show the same sharpness in each of them
Now my question is what you think of the method and if you see any reason to question it or know a better method. To me it is a good method because it eliminates any alignment errors from the user which can easily happen if you use your cupboard for testing. I also wouldn't know a better method so both Jannik and I were a bit flabbergasted by the reaction from Zeiss.The critical point is of course in determining how much of a difference between the corners is too much. Distortion, field curvature and coma are of course affecting and wide angle to varying degrees but I don't really see why they should be a problem, they should affect each corner the same.
Coma is very small in wide-angles. They are usually limited by astigmatism and oblique spherical aberration.
p.1 #19What do you think about this centering test?
Phillip Reeve wrote: zhangyue wroteFor long lens, I can see the merit of this testing. For WA and SWA, I feel this method might be difficult to excude, given it also introduce perspective distortion. especially with lens has FC and coma, sharpness judgement can be difficult and prone to human error. This will introduce complication unneeded IMO.
To have a infinity horizon diagonally cross the frame and Simple focus at center infinity to inspect corner evenness is more robust approach to me.
Phillip Reeve wroteJannik Peters reviewed the Zeiss Loxia 2.8/21 on my blog but he has a decentered copy. When he spoke with a Zeiss representative about the issue he was asked how he tested his lens for de-centering and he answered that he used the Gletscherburch method. Apparently the Zeiss representative ridiculed the method and questioned that Jannik's copy of the Loxia 21 was actually decentered.
The site is in German so a short translation from me:
1) look for an object which has fine details and is at least 20m away, optimally a few hundred meters
2) put the camera on a tripod activate mirror lockup and selftimer or remaote release
3) put the object in the center of the image and focus on it. From now on deactivate AF and do not touch the focusing ring.
4) if your lens isn't sharp in the corners from it's widest aperture stop down to an approriate aperture
5) fix exposure
6) now put the object from step 1 in each of the four corners and take four pictures. The sample image in the link illustrates this step well.
7) when you compare the images the object should show the same sharpness in each of them
Now my question is what you think of the method and if you see any reason to question it or know a better method. To me it is a good method because it eliminates any alignment errors from the user which can easily happen if you use your cupboard for testing. I also wouldn't know a better method so both Jannik and I were a bit flabbergasted by the reaction from Zeiss.The critical point is of course in determining how much of a difference between the corners is too much. Distortion, field curvature and coma are of course affecting and wide angle to varying degrees but I don't really see why they should be a problem, they should affect each corner the same.
My question about this testing are:
A, lens with Astigmatism and coma is hard to judge critical focus at extreme corner this way . For lens having astigmatism, you potential have two focusing location having similar in focus perceptive plane or any optimized focusing between judged by you, hence prone to human error.
B, The focus and recompose error should be negligible in this case, but focusing use corner by moving around camera focal plane is problematic to me, especially for WA and SWA, because it alter light angle hit on the sensor with cover glass which change lens FC and Astigmatism characteristic as well.
Anyway, the difference itself seem strong enough to indicate the decenter but it is really not a optimized way with unnecessary complication IMO.
I think the Lens Rentals method is a good double check, I think using multiple methods to determine if a lens has de-centered elements is far better than to rely on just one.
The plane of focus will not be an issue at infinity - hence why the test will not work if you focus at something that is too close.