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FM Lens test for Centering (Mount tilt / swing)

  
 
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p.8 #1 · FM Lens test for Centering (Mount tilt / swing)


Ix4224 wrote:
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
...Show more

Perform the upside-down method outlined in this thread and analyze the outcomes. I consistently achieve high reliability, indicating that if a lens displays decentering, it does so consistently.



Mar 09, 2024 at 10:31 AM
Fred Miranda
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p.8 #2 · FM Lens test for Centering (Mount tilt / swing)


@yukosteel designed an excellent 3D-printed tool to aid in decentering tests on a tripod. It's a tripod bracket for the Leica M camera, allowing 360-degree camera rotation around the lens's central axis while maintaining focus on the same target when mounted on a tripod ball head.

Download and printed from here: https://www.printables.com/model/897351-tripod-bracket-for-360-degrees-lens-axial-rotation






















Jun 01, 2024 at 09:24 AM
aman74
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p.8 #3 · FM Lens test for Centering (Mount tilt / swing)


Going to try and head out today as it’s the only day predicted to be above freezing and/or not raining or snowing for awhile, and I’d like to get this done soon in case a lens exchange is needed.

I’m a little unsure of how far I’ll need to be for infinity focus, but pretty sure most of these locations will be ok to test between 20-70 from 1.4 to 6.3. (Different max apertures on 6 different lenses).

-I’m assuming too far is also bad? Seems to make sense to me assuming limited resolution (61mp)

-as long as at infinity do all areas we will be looking at need to be close to a similar plane of focus?

-anything need to be done to account for field curvature?

-any chance locking AF would be ok? MF could be a little difficult

I’m going to post some skyline photos that I should be able to get to, some safer areas than others and varying access, but hopefully one suits or I can find something else to photograph.

Hopefully the sample pics post here easily, if not I’ll try and follow-up in a bit after I figure it out (haven’t posted pics here before).

I’m going to try and include pics with a foreground element just so it somewhat lets you know the distance the photographer was from the skyline. A pure skyline we wouldn’t know if a long tele was used.

Last one is an example of one I assume would be too far.

Thanks much!

Well, most all uploads failed for “image size could not be determined”?



Jan 17, 2025 at 10:28 AM
aman74
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p.8 #4 · FM Lens test for Centering (Mount tilt / swing)


Just easier to link the article that shows the locations. I was thinking 1,2,3, and 5

6, I assume is too far?

https://clevelandtraveler.com/cleveland-skyline-views/



Jan 17, 2025 at 10:59 AM
aman74
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p.8 #5 · FM Lens test for Centering (Mount tilt / swing)


Tried today, but the first location was closed, so caused an issue getting to another location in good time. Between the light going down, the cityscape not being quite at infinity, the brutal weather on the lake, etc…I didn’t get it done unfortunately.

Tomorrow will be upper 30’s, but bad rain/snow, then more very cold weather.

I have a couple more questions and really need to make sure I get this done in time. It’s been a journey, quite stressful. Still learning the camera doesn’t help either. A lot of money tied up, with a meager income, so if someone wouldn’t mind PM’ing me to help just a tiny bit it would be much appreciated.



Jan 17, 2025 at 07:51 PM
aman74
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p.8 #6 · FM Lens test for Centering (Mount tilt / swing)




hasenbein wrote:
Not suitable.

Since lenses have more or less field curvature, it doesn't suffice to focus in the middle and then tilt the camera to the 4 corners, leaving focus as is. With the subject in each corner, you have to focus anew (preferable via manual focusing via focus magnifier in EVF) to optimum sharpness each time. The degree to which this optimum achievable sharpness is different in each corner tells you the degree of decentering.


I guess I’m a little lost on this as according to my understanding of the instructions, not refocusing and moving the central target image to each of the 4 corners is what we are supposed to be doing?



Jan 30, 2025 at 12:35 AM
aman74
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p.8 #7 · FM Lens test for Centering (Mount tilt / swing)




Fred Miranda wrote:
Hi all,
I have posted my personal lens decentering/test technique in another thread but it's difficult for some members to find it. I reposted it here so it's easy to bookmark or link to it.

Warning: If you already love your lenses, don't put them through this test. You may get disappointed

------------

Here is a testing method I developed a while back that gives me consistent results and takes less than a minute to perform. Since you will be shooting your target at infinity distance, alignment isn't crucial and therefore won't be a variable to worry about. (Like when using test
...Show more

Are figures one and three supposed to come out in vertical format? I’m guessing not by looking at the full frame shots shown at the bottom.

I have an A7rV with all guide lines on in the VF. I’m taking an image with a target item in the center and then both moving and rotating the camera counter-clockwise to put the target in the top left corner and taking the diagonal line from that target and lining it up with an easy to continue to find item in the frame, so that I can be consistent. The camera is never vertical.

I notice the instructions don’t say to move the camera to get the target into the corner, but if we just rotate the camera the target will obviously just stay in the center.

I’d really appreciate someone’s help. I’m quickly running out of time and don’t know what else to do. Weather here is giving me limited opportunity, along with finding appropriate subjects far enough away, and dealing with disability and life in general.

I know I’m not the only one to have been a bit confused on the directions (not blaming the directions), just that I’m new to digital, have a lot on my plate just learning that. I even joined up with a paid account to contribute, couldn’t get the pics from my links above to load, but still figured it was what I wanted to do to give to the site anyhow.

Help much appreciated. I can’t afford to get stuck with subpar lenses so really need to get some proper tests done asap.

I can’t tell ya how much someone helping or even reaching out on DM as well would be appreciated. I’ve already made one attempt in the frigid cold to two sites that didn’t work out.



Jan 30, 2025 at 12:47 AM
Jonas B
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p.8 #8 · FM Lens test for Centering (Mount tilt / swing)


aman74 wrote:
Are figures one and three supposed to come out in vertical format? I’m guessing not by looking at the full [...]

I can’t tell ya how much someone helping or even reaching out on DM as well would be appreciated. I’ve already made one attempt in the frigid cold to two sites that didn’t work out.


I think you might be over-thinking this. It really isn't complicated. I can try to help, let's see if it works.
Here is an example:

Set you camera to manual focusing, low ISO (perhaps a tripod is needed) and possible lens correction settings to off.






Above: The whole picture. The black building in the center is, measured on map, about 550 meters away and it's a common apartment building. The image is taken a bright day using an A7CR, a 50mm lens at f/2, handheld, focus and exposure values are locked. A 100% crop looks like this:






Above: 100% crop of the center of the image, nothing strange.

Then I change one setting: Exposure compensation 1.5 stop up, or brighter, to compensate for vignetting. Now I take four more images now with the top of the building in each corner of the viewfinder. I don't turn the camera upside down or anything else.(That's not a critical extra finesse, we keep it simple and skip it for now.)

After getting the images i check the five images in a raw converter and enlarge the point of interest to either 100% or 200% depending on the size of the target I found. Preferably check the images in RawTherapee (to see the images without any corrections) and perhaps also your favourite converter.

Here is the 100% crop of the lower left corner just to illustrate what the difference between center and corner can look like:





Above: 100% crop of the lower left of the image, nothing strange. What we are looking for is differences between the four corner crops.

In this case with the A7CR and a Sigma 50i (50/2 Contemporary DG DN) there was no problem. The other corners were pretty much the same as the one showed above. A good result and perhaps better than the average lens. You'll see flaws when testing!

So, I don't do it exactly the same way as Fred, keepcoding or hasenbein does it. The idea however is the same and in my experience it works well enoght to judge if the lens is good enough and to be kept or returned. If I may say so, just go ahead and don't be too worried about the size of the target. Just make sure it is distant enough, I would say not closer than 100 meters or so. I hope this is to some help and good luck with the lens!

EDIT: Some details: low ISO, in-camera corrections and choice of raw converter was added.

Edited on Feb 05, 2025 at 11:22 AM · View previous versions



Jan 30, 2025 at 04:19 AM
aman74
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p.8 #9 · FM Lens test for Centering (Mount tilt / swing)


Hi all, got some pics taken and posted, please have a look and offer your thoughts, I’m in a bit of a rush at this point. Thanks much.

I have one album up so far on Flickr. It’s for my 28-60 at 28, 40, and 60 performed with Fred’s method. Then one set just focusing on the center and moving the target to the corners. That was at 28.

https://flic.kr/s/aHBqjC1op6

I don’t see any large differences comparing corner to corner here. Not sure if overall performance aside from the decentering/tilt test is as expected. It’s seems like it’s a good one….aside from the top left corner darkening more than the rest?

Here is the album for the 20-70 @20, 28, 35, and 50 (I noticed the same darkening mentioned about the 28-60, but since on this one it seems to effect both top corners it seems perhaps it’s not a flaw with the 28-60 top left corner, but perhaps more just the shooting conditions?

https://flic.kr/s/aHBqjC1oHn

This is for the 24 GM, top left dark again, baffling to me, I’m sure someone here will have an explanation. If it was a sensor or mount misalignment I’d expect the photos to be off in other ways as well. In this series I also did a mid-frame test since it’s a faster lens and Fred had suggested that at one point. The one merely labeled “mid” is the center shot as anytime I changed what I was testing for like mid-frame or edges or switched the other testing method I took a new center shot.

https://flic.kr/s/aHBqjC1tFW

50 1.2 GM Fred’s test and a Mid-field test

https://flic.kr/s/aHBqjC1v6W

Sorry for any labeling confusion, this took many days between shooting, learning a new camera, and then trying to do this with just LR on my phone with no card reader, etc… ( I could write a book with all the issues that popped up with that including why does LR CC add sharpening and denoise to all imports), that alone took forever to undo, not to mention I had to upload to Sony’s Creator App and then transfer to LR where it then proceeds to change the file name.

Thanks much for looking.



Feb 05, 2025 at 02:49 AM
Jonas B
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p.8 #10 · FM Lens test for Centering (Mount tilt / swing)


aman74 wrote:
Hi all, got some pics taken and posted,


...or a whole bunch of images, lol.

Hi,
I got a little dizzy by looking at so many leaning images. The second 28mm series was nice! ;-)

I have no experience with any of the tested lenses. The lateral CA at the wide end of the zoom lenses felt a bit much and that with correction for CA applied. Perhaps its totally normal and then again, the wide end, well, some CA is to be expected.

28-60mm:
@28 The CA... otherwise OK to my eyes
@40 and 60 mm, OK

20-70mm zoom:
Hmm. I'm not sure what to think. What does normal images look like?
@20mm: right side worse
@28mm: right side worse
@35mm: the same
@50mm: left side now clearly worse.
I have no idea about if this is normal or not for this lens.

24GM:
OK. There is a midframe drop but it's not that bad.

50GM:
OK. Yes, there is a slight midframe drop here as well but, again, probably OK.

All in all I think your lenses are OK and should be kept and used for imagemaking! But, let's see if you get any comments on the 28-70 G lens!

I notice I missed a couple of things in my earlier post in this thread. Use a tripod if needed to get low ISO! High ISO is normally OK but not so good when checking "sharpness". Turn off in-camera lens corrections. Preferably check the images in RawTherapee (to see the images without any corrections) and perhaps also your favourite converter.
I'm sorry for that and will edit my post (#8 on this page).



Feb 05, 2025 at 11:17 AM
 


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aman74
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p.8 #11 · FM Lens test for Centering (Mount tilt / swing)


@Jonas B

I can get into details another time, and try and redo some tests, though by then I’ll be past my return period.

In the meantime the most pressing issue seems to be the darkened corner(s) since it’s happening across all lenses, mostly and much stronger in the top left corner and sometimes to a lesser degree in the top right corner.

That’s not something I would know what to make of, and wondering if I need to exchange the camera body ASAP?

The 20-70 is known to be weak in the corners from at least 20-28 so not sure how to evaluate it exactly.

The 24 gm I thought would be a little sharper? I may have a focus error there.

On the slow zooms I probably should have dropped the shutter speed a bit more to get to ISO 1600. Was a gloomy day. Fred mentioned really focusing on a super high shutter speed over ISO concerns so I leaned that way.

I do see the differences between sides in some examples, mostly the zooms, but since most lenses, especially zooms, are not going to be perfect, and all zooms are said to have some tilt, the differences in corners relative to each other seemed small (?) compared to some examples of lenses I’ve seen posted, but I’m no expert, and this is a torture test and a different type of experience needed to evaluate, so really appreciating you and hoping for more opinions here. I see the thread getting read and the photo albums so really hoping.



Feb 05, 2025 at 04:54 PM
aman74
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p.8 #12 · FM Lens test for Centering (Mount tilt / swing)


I don’t know if this will help solve the issue of the darkened corners or not. Exposures all the same.

First set is the “standard” way with the 50 1.4 gm, second is the 20-70 Fred’s way.

Seeing the amount of sky above the buildings the standard way made me think about it, but do it Fred’s way that’s not so much a factor, so I posted both sets.

These are RAWs from Sony’s app, my Flickr posts are sent from the Sony app to Lightroom. I really have no idea what settings Sony applies and the relationship between that and sending them to LR. First impressions seem to imply they look better out of the Sony app.

Scratch that, whatever happened between transferring RAW files from the Sony app to files on my phone, exporting them to another folder as jpegs, and then exporting to here, seems to have hurt the image quality in a big way. That won’t matter for this particular posting though.










































Feb 05, 2025 at 11:14 PM
Jonas B
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p.8 #13 · FM Lens test for Centering (Mount tilt / swing)


I thought you should get more replies.
Maybe starting one or two new threads for the zoom lenses? Like "20-70/4 G - Is this normal?"



Feb 06, 2025 at 07:57 AM
Jonas B
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p.8 #14 · FM Lens test for Centering (Mount tilt / swing)


About the dark upper left corner.
I think it's normal, something about light, angles and particles in the air or, well something. When at home, take a shot at something white evenly, or as evenly as possible, lit surface. Perhaps a fridge door, a grey wall, a white t-shirt, use your 50mm lens, set it to infinity, +1.5 exposure comp, and a large aperture. Shutter speed and ISO doesn't matter, in fact a long shutter making the image totally blurry is no drawback. Now go close to the subject, make it fill the image completely.

Is the upper left still significantly darker than the rest of of the image?



Feb 06, 2025 at 08:58 AM
aman74
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p.8 #15 · FM Lens test for Centering (Mount tilt / swing)


Yeah, can’t say I’m not a little disappointed, but I saw a lot of others post as well and not hear anything so I don’t feel singled out. Some did say they’d help, but maybe they got busy.

Perhaps another thread if I can find the energy. Your time has been appreciated. It’s been a journey over here, dealing with a daunting new system and getting these tests done, then the transfer and PP on not exactly the right or easiest devices….all while in treatment for a tumor, and then my mom ends up in the hospital twice.

In looking over the thread and seeing other people’s posts, which most the pics are gone or they didn’t get feedback, but the one’s that did and deemed good mine seem to be the equal of or surpass and the one’s that were definitely off you can really see it. Some were closer calls. I also just don’t have the experience.

I’m gonna do more testing when weather and life permits, even if my return date is over.

Jonas B wrote:
I thought you should get more replies.
Maybe starting one or two new threads for the zoom lenses? Like "20-70/4 G - Is this normal?"




Feb 06, 2025 at 03:50 PM
aman74
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p.8 #16 · FM Lens test for Centering (Mount tilt / swing)


Ok, I’ll try that. I guess it’s the scene then you’re referring to with that phenomenon? When I’ve seen it in other tests it’s usually because they didn’t lock exposure. It’s just weird that since it’s the same target shot it just happens mostly there and somewhat on the top right as well. When I lighten it up it compares much more favorably with the other corners.

The noise is definitely an issue.

The 24 I think is a misfocus as I had to use AF and the focus point, even at its smallest, may not have hit perfectly accurate. I think that lens is probably capable of being a bit sharper? I know it’s not the equal of the new GM’s in sharpness, but I think could do a bit better, though some say it’s more of a character lens and don’t rate it. Some love it. That one was used so not as much of a hurry to confirm.

The 35gm, 50 1.4 and 1.2 gm’s don’t leave anything to be desired from what I can see, so I didn’t even post the 35 and other 50 for fear of having too much for people to take a look at.

It was really overcast, and there’s some haze from distance, but I don’t think anything from heat differential.

As for the lens correction on on the zooms, that wide end is too wide with it off to get an accurate framing, unless it still shows the corrected image in the Vf when shooting, and the parts it cuts off are pretty bad, and the 20-70 heavily relies on it to where I wouldn’t be using the lens without it on, so I figured it was reasonable to use.

I didn’t mean to leave the CA correction on on the 28-60, but going back and flicking it on and off it seems to do nothing in LR on my phone….but file handling has been its own can of worms between trying to get the images off the cam with no card reader, only having a phone at the moment, Sonys app and LR CC making a mess of the order of the files, even when telling it to sort by date/time.



Jonas B wrote:
About the dark upper left corner.
I think it's normal, something about light, angles and particles in the air or, well something. When at home, take a shot at something white evenly, or as evenly as possible, lit surface. Perhaps a fridge door, a grey wall, a white t-shirt, use your 50mm lens, set it to infinity, +1.5 exposure comp, and a large aperture. Shutter speed and ISO doesn't matter, in fact a long shutter making the image totally blurry is no drawback. Now go close to the subject, make it fill the image completely.

Is the upper left still significantly
...Show more



Feb 06, 2025 at 04:05 PM
Jonas B
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p.8 #17 · FM Lens test for Centering (Mount tilt / swing)


aman74 wrote:
Ok, I’ll try that. I guess it’s the scene then you’re referring to with that phenomenon? [...]
The noise is definitely an issue.
[...] only having a phone at the moment, Sonys app and LR CC making a mess of the order of the files, even when telling it to sort by date/time.

Yes, I'm referring to the scene.
The noise, yes, it's disturbing when checking sharpness, in real world photography I'm not as concerned. Your lenses are short lenses. You should easily be able to get sharp handheld images at lower ISO-values if you don't have a tripod.

But really, i don't
...Show more

?

/Jonas



Feb 06, 2025 at 04:14 PM
aman74
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p.8 #18 · FM Lens test for Centering (Mount tilt / swing)


Yeah, Fred focused on really high shutter speeds as well as some others saying the same, so I didn’t want to deviate too much, but I should have just done another round once I had accomplished all the testing and knew I still had time.

New computer and monitor in the spring so I can really get back into the swing of things.

I have an old Bogen 3021 with a three way head that my hands wouldn’t have appreciated too much

Formatting on your reply didn’t quite work, but I think you’re asking if the upper left is still dark after testing again? I’ve not done the test you recommended yet. I’ll do that tonight to make sure the camera is ok. I’m sure you’re right.

Jonas B wrote:
?

/Jonas




Feb 06, 2025 at 04:38 PM
aman74
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p.8 #19 · FM Lens test for Centering (Mount tilt / swing)


Oh, and I did want to see about the CA on the 28-60. I wouldn’t have expected it on a slow zoom stopped down a step. Weird that LR isn’t picking it up as it’s not LOCA

I’ll try and get some real world shots from both the zooms soon, especially the 20-70 and see what I think.

Jonas B wrote:
?

/Jonas




Feb 06, 2025 at 04:43 PM
weatherproof
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p.8 #20 · FM Lens test for Centering (Mount tilt / swing)


Fred Miranda wrote:
Warning: If you already love your lenses, don't put them through this test. You may get disappointed

------------

Here is a testing method I developed a while back that gives me consistent results and takes less than a minute to perform. Since you will be shooting your target at infinity distance, alignment isn't crucial and therefore won't be a variable to worry about. (Like when using test charts at close distance)

...


Hi Fred, it looks like https://www.fredmiranda.com/forum/ufiles/27/1610727.jpg might be unloadable right now.

Secondly, is it possible to upload a version of the instructions where the "bottom" is noted as one rotates the camera? I can't seem to grasp the star and circle concept.

Thank you!



Jul 28, 2025 at 08:49 PM
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