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Problem with 24-105mm F:4 G OSS lens


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#1 denniswcr

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Posted 09 January 2018 - 06:58 PM

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When I saw the introductory photos taken with the Sony a7RM3 outfitted with the new 24-105 F:4 G OSS I was very impressed and felt it was time for me to change from my Nikon D800 to the Sony mirror-less system.I purchased an a7RM3 withthe new 24-105 G, the 100-400 F:4.5 GM and the 16-35 F:2.8 GM.This combination provides a nice overall system with a nice walk around lens.

I proceeded to run some quality tests on the system with all of the lenses and have found a problem with the 24-105.I photographed an old lens test chart that I had put together in my film days.It uses the NBS 1952 lens resolution charts.The charts are placed in the center and corners of the frame.

The 100-400 GM and the 16-35 GM both tested very well with 80 lines/mm everywhere in the frame, center and corners.I tested the lenses at min, max and central focal lengths.

The 24-105 G, however, is quite different.It tested very well with 80 lines/mm across the frame at min and max focal lengths, I was quite delighted.When I went to 60mm the results were not good at all and when I tried stopping down to F:8 the results were even worse.The problem I see is that the left side of the frame is very soft while the center and right side test okay.The NBS test charts have a thin lined circle in the center and that thin line becomes doubled when it is tangent to a radius drawn from the frames center.I returned the lens to B&H and they replaced it with another new one.The second lens exhibits the same problem.Since my other two lenses test okay, and the 24-105 tests okay at min and max focal lengths I feel quite certain that the problem is with the 2 lenses tested and not the camera body.

I am beginning to wonder if I just got units from a bad run or if there is a mechanical design error in the zoom rails causing misalignment.I realize that for a great many photos this is not too great a problem, but when photographing flat surfaces it does show up.When I shot a brick wall, left side softness was quite apparent in the mortar and brick texture.I am thinking seriously of sending the second lens back and getting the 24-70 F:2.8 GM even though it is very heavy and does not have OSS. 

 

Has any one on the Forum seen a similar problem?



#2 tinplater

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Posted 09 January 2018 - 11:36 PM

Just for fun, after reading your post, I took a photo of my stucco wall with a horizontal crack and at F4 60mm the left side is marginally sharper than the right.However this was just hand held shooting my wall without tripod, etc.To this point I have been totally happy with the lens, and in more carefully controlled tests it outperformed my Sigma (Canon mount adapted).



#3 Jaf-Photo

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Posted 10 January 2018 - 06:57 AM

In nu experience, decentering in zooms show up more at certain focal lengths at certain focal distances and certain f-stops. So, your results would not be unusual for a decentered zoom. Whether this lens would be constructed to be decentered at certain settings, I doubt it. In any case you should do something about it, having the lens returned, replaced or realigned. Over time, the annoyance would just grow on you.

On a side note, I once had a Canon camera where the sensor was misaligned. It would only be prominent with some lenses at certain settings. The problem went away after Canon realigned the sensor.

#4 denniswcr

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Posted 10 January 2018 - 12:03 PM

In nu experience, decentering in zooms show up more at certain focal lengths at certain focal distances and certain f-stops. So, your results would not be unusual for a decentered zoom. Whether this lens would be constructed to be decentered at certain settings, I doubt it. In any case you should do something about it, having the lens returned, replaced or realigned. Over time, the annoyance would just grow on you.

On a side note, I once had a Canon camera where the sensor was misaligned. It would only be prominent with some lenses at certain settings. The problem went away after Canon realigned the sensor.

Thanks for that information



#5 denniswcr

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Posted 11 January 2018 - 09:35 PM

For those that would like to view the test file here is a link to a JPG of it on Microsoft OneDrive.  https://tinyurl.com/yb5cmmo7


The JPG was made from the RAW file in PhotoShop CC. Once you see the file click on it to see the image not a thumbnail. Then click "View Original" to bring up the file as uploaded.Now you can click anywhere on the image to see a magnified view, and compare the left side, center, right side.The file can also be downloaded if you wish to view in PS.



#6 denniswcr

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Posted Yesterday, 06:02 PM

I received the Sony 24-70mm F:2.8 GM lens to replace the 24-105 F:4 G.This lens works as it should, 80 lines/mm corner to corner at all focal lengths.I really would have preferred the 24-105 as a general shooting lens but could not seem to get a good one.




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