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09-19-2021, 11:16 AM   #1
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Can IBIS soften a part of an image? Pentax K-3

Hello!

I noticed a strange behavior on my K-3 - a part of an image is noticeably softer than the the rest.

Long story short:

I've bought a DA 50-135 more than half a year ago and it turned out to be decentered - I noticed a consistent softness throughout the zoom range, which only affected one side - the left. The center was sharp, right side a bit less, but acceptable, and the dar to the left the worse it got. I send it to service where the supposedly changed 2nd lens group, did some calibration and sent it back to me after 2 moths. I tested it again and that day everything looked fine. Then my gear spent most of the time in a closet.

Now I recently acquired a DA 18-55 WR and this problems seems to be back. Before that however I finally took my Pentax out of the closet a few weeks ago I took some pictures. Later that day looking on them on my computer I noticed that the left side is much softer that the right, what got me. I was expecting delivery of the DA 18-55, so I thought I'll take them both to a "field test". My first field test was taking photos of a wall at a distance of ~10m, on tripod, self-timer, LV, 5 focus points (center + corners). Both of them showed no decentering issue (DA 18-55 was more uneven, but it's acceptable in its class). Then I took them to a park, when I had a chance to take photos where lenses' focus distance was set to exact or near infinity. Same story as above - tripod, self-timer, LV, and the results where the same - both seemed to achieve similar sharpness when comparing two opposite sides.

Things got strange when I took the camera out of the tripod and shot handheld. Then I noticed that a few photos had that kind of "de-centering" issue (both lenses). I think that the common ground for both lenses is that the IBIS was enabled in the photos, that were shot handheld, but it's not the case where every shot with IBIS ON was defected. There is a few days left for my DA 50-135 repair warranty, so I would like to know if that could be a body issue (particularly IBIS; Pentax K-3) or it's lenses'.

Currently I have a problem with taking a photo on command, that would show this issue. I took additional tests, but so far I have trouble to point out the deciding factor here.

Do anybody have any knowledge of this type of issues? Is there a way to accurately test it, so I can be sure where's the devil?

Any help would be appreciated.


Last edited by Coven; 09-19-2021 at 12:17 PM.
09-19-2021, 12:46 PM   #2
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Use center point only AF when doing your hand-held tests.

Question...Are you using horizon correction, by any chance?


Steve
09-19-2021, 01:03 PM   #3
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Nope. All shots were done in Manual mode and RAW format. I indeed used center focus point. I always try to get as perpendicular as I can to my subject when I'm testing lenses.

Here's comparison on one of the first photos I saw this effect. I think I have the highest ratio between good and bad shots that day (when I firstly grabbed my gear after a long time).
https://imgur.com/a/VbFMvuN

Last edited by Coven; 09-19-2021 at 01:23 PM.
09-19-2021, 03:54 PM   #4
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An you manually focus using live view handheld and test that way?

09-19-2021, 07:18 PM   #5
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QuoteOriginally posted by UncleVanya Quote
An you manually focus using live view handheld and test that way?
Did you see the examples provided on imgur?


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09-19-2021, 07:58 PM   #6
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QuoteOriginally posted by stevebrot Quote
Did you see the examples provided on imgur?


Steve
Sort of?. 1) I don't use that service so I don't have a login. 2) I use an ad blocker that it doesn't like. I did see a 3 part image (one large and two smaller images) but couldn't figure out how they related to each other exactly. I think I'm seeing left and right side of the image - but I don't have context enough to know what it should look like at this distance.
09-19-2021, 08:51 PM   #7
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QuoteOriginally posted by UncleVanya Quote
Sort of?. 1) I don't use that service so I don't have a login. 2) I use an ad blocker that it doesn't like. I did see a 3 part image (one large and two smaller images) but couldn't figure out how they related to each other exactly. I think I'm seeing left and right side of the image - but I don't have context enough to know what it should look like at this distance.
Blurred one is left horizon sharp one from the hard right.

09-19-2021, 11:07 PM - 1 Like   #8
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QuoteOriginally posted by Coven Quote
Do anybody have any knowledge of this type of issues? Is there a way to accurately test it, so I can be sure where's the devil?
I've checked your images. The devil is zooming-in 100% on very far distant trees. Far distant tree target isn't a good choice to test a lens, there is atmospheric haze and far features details are smaller than pixel pitch. And image details on the left side are further away from the camera than image details on the right, explains why the right side looks "sharper", tree leaf visible on the right, but mushy on the left due to distance. If you want to test the lens , use a newspaper flat on a wall with lens axis perpendicular to the wall.
Anyway, I don't see left or right being pixel sharp, at that distance the camera can't resolve most detail in the scene, both sides are blurred to some degree due to tendency of all lenses to resolve less at edges relative to center, zooms tend to be worse than prime lenses in terms of center to corner sharpness drop.
Is the resolution on the left side limiting when you print your photos? If yes, I would consider using a prime lens, or getting a larger format camera (Pentax K1 or 645z). Trying to improve on this 50-135 lens sharpness isn't going to get you much return on time spent.

Last edited by biz-engineer; 09-19-2021 at 11:13 PM.
09-20-2021, 07:18 AM   #9
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QuoteOriginally posted by Coven Quote
Nope. All shots were done in Manual mode and RAW format. I indeed used center focus point. I always try to get as perpendicular as I can to my subject when I'm testing lenses.

Here's comparison on one of the first photos I saw this effect. I think I have the highest ratio between good and bad shots that day (when I firstly grabbed my gear after a long time).
Imgur: The magic of the Internet

Sorry, that image (and its magnified crops) are quite useless for checking whether you have a problem. You really would be better photographing a brick wall or a rock face that filled the frame so that details are clearly bigger in the image than pixel size. Or perhaps a monumental inscription.

Have another go.
09-20-2021, 08:48 AM   #10
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What I expected to see was a set of two identical shots. Shot 1 made with tripod using all the same settings other than self timer and tripod vs Shot 2 handheld with IBIS. I then expected to see a comparison of both right sides and both left sides showing that the IBIS enabled shot was decentered vs the tripod one. Obviously the shutter speed selected needs to be high enough to work reliably in the handheld version.
09-20-2021, 04:09 PM   #11
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I would check the camera mount and make sure you don't have a loose screw or two on one side.
09-20-2021, 05:03 PM   #12
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I have never seen such focus problem cause by SR with my K3.
I had seen a similar problem with K3 and my old DA15 which the left/right edge noticeably softer. But it was lens curvature effect. My problem with DA15 had nothing to do with SR. It had to do with where I select to focus. Once I select to focus on the right place, there were no blur problem anywhere on the image.

As many has already said, I think it might be a good idea to do a few more test shots with the same scene one on a tripod, one not - SR on / off and let us know where is the focus point and what is the focal range. Ideally don't use subject can be swayed by the environment.

Last edited by tokyoscape; 09-20-2021 at 05:14 PM.
09-20-2021, 07:43 PM   #13
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My da 50-135 has always seemed rock solid image size.
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