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FM Lens test for Centering (Mount tilt / swing)

  
 
Maknof
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p.7 #1 · p.7 #1 · FM Lens test for Centering (Mount tilt / swing)


Jonas B wrote:
At first glance i wouldn't be too happy about an expensive prime performing like that. A second look tells me the exposure difference between the images is close to two full stops and it make it harder to judge. But, to me it seems as left side is better, you may have some swing or a slightly decentered element....
.

Fred Miranda wrote:
It looks like you used shutter speed priority and therefore the exposures are not equal.
I would advice shooting in manual exposure and make sure I turn IBIS 'off'.


Thank you, i forgot both autoiso and AE Lock, i made a 2nd try with less light and
result is the same, i have ibis always off, it is a 100% crop, the electric tower is 700-750 feet far


For reference FE28 @ f/2.5 i framed differently only to make the tower touch the corner and shot the test faster and for me it perform very well.



I prepare a pack to send back this Loxia to Amazon.



May 16, 2021 at 03:52 PM
Fred Miranda
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p.7 #2 · p.7 #2 · FM Lens test for Centering (Mount tilt / swing)


Maknof wrote:




Thank you, i forgot both autoiso and AE Lock, i made a 2nd try with less light and
result is the same, i have ibis always off, it is a 100% crop, the electric tower is 700-750 feet far


For reference FE28 @ f/2.5 i framed differently only to make the tower touch the corner and shot the test faster and for me it perform very well.



I prepare a pack to send back this Loxia to Amazon.


I would exchange it.



May 16, 2021 at 04:01 PM
Duowing
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p.7 #3 · p.7 #3 · FM Lens test for Centering (Mount tilt / swing)


Here's my second 35 GM. I'm looking for some feedback. Is this a keeper or am I over analyzing these crops. This one is definitely better than my first copy.





Sorry for any multiple edits people suffered through as I tried to relearn how to embed photos.



May 25, 2021 at 02:30 PM
hasenbein
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p.7 #4 · p.7 #4 · FM Lens test for Centering (Mount tilt / swing)


The two upper ones are exposed lower, so comparison is difficult. Please always expose evenly between the 4 images!


May 25, 2021 at 11:12 PM
weirdo021
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p.7 #5 · p.7 #5 · FM Lens test for Centering (Mount tilt / swing)


Hi, tried this for the first time on my 35 GM. Does my lens look good?

Test pic 1
Test pic 2
Test pic 3
Test pic 4



May 26, 2021 at 01:13 AM
Maxbot
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p.7 #6 · p.7 #6 · FM Lens test for Centering (Mount tilt / swing)


Thanks Fred for sharing the info on the decentering test, I've used it a fair few times over the years to check my lenses. I just tested my 35 GM today, and I noticed something I have never seen before. Two of the corners appear slightly softer than the other two @ 1.4, but stopped down to 2.8 the four corners appear identical. Just wondering whether this is a normal phenomenon, thanks!


Jun 16, 2021 at 08:49 PM
lifeandmylens
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p.7 #7 · p.7 #7 · FM Lens test for Centering (Mount tilt / swing)


Bought a mint copy of a Leica 90-280 from a dealer. Just arrived...decentered! Will be going back

I like this test because it shows you on the first try if it's decentered or not. I, however, duplicated it about 10 times just to be sure..all the same results. And a ~$6k lens it better be near perfect






















Dec 07, 2021 at 04:25 PM
lifeandmylens
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p.7 #8 · p.7 #8 · FM Lens test for Centering (Mount tilt / swing)


Just posting in case it helps anyone. My post right above this was an example of a decentered lens I wouldn't be happy with. Exchanged it for this one and you can see the difference.












Dec 10, 2021 at 03:47 PM
yeyiren
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p.7 #9 · p.7 #9 · FM Lens test for Centering (Mount tilt / swing)


OMG, I just find the problem is my camera's mount is crooked..most of my lens can get the infinity on the right, but on the left, I need turn back a bit to get the infinity


Dec 30, 2021 at 10:59 PM
keepcoding
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p.7 #10 · p.7 #10 · FM Lens test for Centering (Mount tilt / swing)


yeyiren wrote:
OMG, I just find the problem is my camera's mount is crooked..most of my lens can get the infinity on the right, but on the left, I need turn back a bit to get the infinity


Which camera?
Have you repeated the test without flipping the camera upside down?



Dec 31, 2021 at 02:04 AM
 


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yeyiren
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p.7 #11 · p.7 #11 · FM Lens test for Centering (Mount tilt / swing)


sony A7R3. So many test, no well centering lenses, but the same trend. So I doubt the camera.

It is easy to test the mount I think, you can feel the difference between the peak focus at the extreme right and left of the image.

For example, the right could be focused on the infinity stop of the focus ring, but the left will meet the infinity before the stop.



Dec 31, 2021 at 03:40 AM
Fred Miranda
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p.7 #12 · p.7 #12 · FM Lens test for Centering (Mount tilt / swing)


bump as I'm getting a lot of questions about this lately.


Feb 17, 2024 at 03:11 PM
David Baldwin
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p.7 #13 · p.7 #13 · FM Lens test for Centering (Mount tilt / swing)


If I buy a new lens I wait for the next clear night, and photograph the stars (on a tripod). I set the aperture to wide open, and use an exposure length just short enough to prevent the stars appearing to move. This is a quick test but it really allows all four corners to be compared in one exposure. Differences in the corners will be very easy to see.


Feb 18, 2024 at 06:51 PM
chiron
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p.7 #14 · p.7 #14 · FM Lens test for Centering (Mount tilt / swing)


Fred Miranda wrote:
bump as I'm getting a lot of questions about this lately.


Fred,

What is the rationale for turning the camera upside down for half the shots rather than simply shooting all four corners right side up?

The problem (at least for me) with turning the camera upside down is that it makes it harder to hold the camera steady while releasing the shutter. I think that may affect the results with the upside down shots.



Feb 18, 2024 at 08:00 PM
Fred Miranda
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p.7 #15 · p.7 #15 · FM Lens test for Centering (Mount tilt / swing)


chiron wrote:
Fred,

What is the rationale for turning the camera upside down for half the shots rather than simply shooting all four corners right side up?

The problem (at least for me) with turning the camera upside down is that it makes it harder to hold the camera steady while releasing the shutter. I think that may affect the results with the upside down shots.


You can also do that. When I flip it upside down, I can see the corners more clearly because they match the exact same pattern, like a mirror image. I also can easily see the progression from mid-zone to extreme corners. Some fast lenses may show similar corner performance but could have decentered mid-zones.



Feb 18, 2024 at 08:06 PM
RT--
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p.7 #16 · p.7 #16 · FM Lens test for Centering (Mount tilt / swing)


Instead of shooting with the camera upside down, shoot vertically; two corners with the grip up, and the other two with the grip down.

If you don't flip the camera, it will be difficult to compare the images unless your target is a siemens star.



Feb 19, 2024 at 12:39 PM
Fred Miranda
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p.7 #17 · p.7 #17 · FM Lens test for Centering (Mount tilt / swing)


lifeandmylens wrote:
Bought a mint copy of a Leica 90-280 from a dealer. Just arrived...decentered! Will be going back

I like this test because it shows you on the first try if it's decentered or not. I, however, duplicated it about 10 times just to be sure..all the same results. And a ~$6k lens it better be near perfect


It happens with high-end lenses as well including tight tolerance Leica lenses. With zoom lenses, it's nearly impossible to achieve perfect centering at all focal lengths. You may think your lens is perfectly centered but that's until you get a higher MP body and see it's not the case.



Feb 23, 2024 at 05:13 PM
highdesertmesa
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p.7 #18 · p.7 #18 · FM Lens test for Centering (Mount tilt / swing)


Fred Miranda wrote:
You can also do that. When I flip it upside down, I can see the corners more clearly because they match the exact same pattern, like a mirror image. I also can easily see the progression from mid-zone to extreme corners. Some fast lenses may show similar corner performance but could have decentered mid-zones.


Could you fully elaborate on decentered midzones? If midzone is defined as the four intersections of the rule of thirds, do they usually show as decentered at two intersections on the same side of the frame? Can you have only one of the four intersections decentered? Can they happen with sharp center and all four sharp corners?



Feb 23, 2024 at 06:38 PM
Fred Miranda
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p.7 #19 · p.7 #19 · FM Lens test for Centering (Mount tilt / swing)


highdesertmesa wrote:
Could you fully elaborate on decentered midzones? If midzone is defined as the four intersections of the rule of thirds, do they usually show as decentered at two intersections on the same side of the frame? Can you have only one of the four intersections decentered? Can they happen with sharp center and all four sharp corners?


With fast lenses, the shape of their field curvature can sometimes cause false positives. This means that the very corners may appear equally sharp, while there are differences in the mid-zone. It's not necessarily that the lens is decentered at the mid-zone, but rather that's the area where tilt or swing is noticeable.



Feb 24, 2024 at 05:19 PM
Ix4224
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p.7 #20 · p.7 #20 · FM Lens test for Centering (Mount tilt / swing)


I just got a new lens and going through this decentering test but I'm having issues with consistency. I'm performing the test right-side up only instead of doing the upside down method as I thought this would be more consistent.

I've run through the lens many times (about a dozen) using a different distant building/sign/pole each time and I'm getting very inconsistent results. Sometimes I'll see that top left corner is a bit softer, sometimes it's the bottom right corner and other times all corners look roughly equal.

I'm making sure to use electronic shutter, IBIS off, manual exposure only and handheld at high shutter speeds (>1/1000).

Am I doing something wrong here? The distance for each subject has varied a bit (I don't have a good super far distance subject to use) so I wonder if it's some combination of field curvature + the amount of movement to the corners from the initial center picture has varied.



Mar 05, 2024 at 09:12 PM
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