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07-24-2016, 04:14 AM - 1 Like   #1
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Help needed figuring out D FA 28-105

I admit I'm flummoxed. I have tried all my lenses on the K-1, and they all perform as expected or better ... except for the D FA 28-105.

With that lens, I do get many shots that look great. However, some look weirdly maniacal when I zoom in, particularly images of foliage or bare branches. For example, here's a pretty simple image (28mm, 1/125 sec, f/7.1, ISO200):



But here's a crop zooming in on the branches, leaves and rushes:



It looks demented, disturbing! In fact, it looks like a slightly shifted double image. I keep getting this from the 28-105, but from no other lens.

Can anybody suggest a reason? Has anyone seen similar behaviour with their copy of this lens? No filter is attached.

07-24-2016, 05:07 AM   #2
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Hi Paul,

If you look at the quick review I posted of the 28-105 when it and the K-1 first came out [lens review], I got similar results fully open that lacked microcontrast and sharpness. The overall result when not pixel-peeped looks great, especially for closer shots with pleasant bokeh backgrounds. Though even stopped down the fine detail is lacking on landscapes.

For me it is very much like the 18-135 on the K-5: a convenient lens that can produce pleasing results some of the time at 16mp. The 28-105 on the K-1 has the advantage of 36mp from which to down-sample from, and hence a consequently better keeper rate.

If the weather is not great, I use the 28-105, otherwise I much prefer the results I get from old F series primes; they out resolve the sensor most of the time and have that certain Pentax magic.

On the plus side with other standard zooms, the 28-105 has light weight, small size, WR, fast/quiet focus and price. I have not got the D FA 24-70 to compare against, but I have got an old Sigma 24-70 that is much bigger and heavier, but a bit better in the IQ department.

Chris
07-24-2016, 05:20 AM   #3
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You weren't using a tripod or support with SR still turned on were you? I think that can produce results like this.....

My test results (on K-1) don't show this odd unsharpness, it DOES look like your image shows image or sensor movement.
07-24-2016, 05:23 AM   #4
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QuoteOriginally posted by phoebus Quote
If you look at the quick review I posted of the 28-105 when it and the K-1 first came out [lens review], I got similar results fully open that lacked microcontrast and sharpness.
Thanks Chris. However, I think it's more than that. If you look at the yellow reeds at the centre bottom, it is apparent that there's a double image. I can also see that in the green reeds if I look carefully.

The image was taken hand-held at 1/125 sec with SR on. But if there's something screwy going on with the SR, why is it only with this lens?

07-24-2016, 05:42 AM   #5
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QuoteOriginally posted by Paul the Sunman Quote
Thanks Chris. However, I think it's more than that. If you look at the yellow reeds at the centre bottom, it is apparent that there's a double image. I can also see that in the green reeds if I look carefully.

The image was taken hand-held at 1/125 sec with SR on. But if there's something screwy going on with the SR, why is it only with this lens?
Could this be a pixel shift resolution problem? Have you tried to turn it off with this lens?
Have a nice day.

---------- Post added 07-24-16 at 05:48 AM ----------

https://www.dpreview.com/reviews/k1-pixel-shift-resolution-updated-field-test

I found this article, and i really think this could be the issue with pixel shift.
I guess sometimes it's better to turn it off. Or it's a combination of camera versus lens.

It could also be a question of post processing software issue.

Have a nice day.

Last edited by ygagne1008; 07-24-2016 at 05:53 AM.
07-24-2016, 06:18 AM   #6
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Paul - is it only happening at certain shutter speeds? For intance, if you keep the shutter speed considerably higher or lower, do you still get the problem? How about SR - does it only happen with it on, or off too?

I'm wondering if this is shutter induced. Have a read of this article - interesting... EDIT: Also, this article. Both are related to the K-7, but I suspect the problem is possible in any camera.

Last edited by BigMackCam; 07-24-2016 at 06:36 AM.
07-24-2016, 06:27 AM   #7
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I think it is due to SR
07-24-2016, 07:06 AM   #8
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QuoteOriginally posted by phoebus Quote
Hi Paul,

If you look at the quick review I posted of the 28-105 when it and the K-1 first came out [lens review]Though even stopped down the fine detail is lacking on landscapes.

For me it is very much like the 18-135 on the K-5: a convenient lens that can produce pleasing results some of the time at 16mp. The 28-105 on the K-1 has the advantage of 36mp from which to down-sample from, and hence a consequently better keeper rate.

Chris
I couldn't disagree more, Chris. The 28-105 is leaps and bounds better than the DA 18-135, and I own a really nice copy of the DA. Corner sharpness, bokeh, color rendition--the D-FA wipes the floor with the DA. My 2 ¢

07-24-2016, 07:14 AM   #9
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125 is not very fast if you are looking for crops from dense foliage while trying to avoid any movement interruption. A tripod test may tell more about the difference shooting at any speed, handheld or during use of tripod. In dense areas the contrast is sometimes a challenge, due to plain lack of it.
07-24-2016, 07:25 AM   #10
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QuoteOriginally posted by phoebus Quote
For me it is very much like the 18-135 on the K-5: a convenient lens that can produce pleasing results some of the time at 16mp.
I wrote a user review pf the D FA 28-105mm lens at DPReview.

I found this lens to have very high image quality right to the corners of my K-1, even when I pixel-peep.

So does ePHOTOzine in their review of it.

QuoteOriginally posted by Fat Albert Quote
I couldn't disagree more, Chris. The 28-105 is leaps and bounds better than the DA 18-135, and I own a really nice copy of the DA. Corner sharpness, bokeh, color rendition--the D-FA wipes the floor with the DA. My 2 ¢
I haven't compared the 28-105mm with that lens, but I agree with your general assessment of it.
07-24-2016, 08:41 AM   #11
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That looks like motion blur to me, but here is some helpful advice from Matt Damon:

07-24-2016, 08:43 AM   #12
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Looks like motion blur. From the examples shots of the reviews, what i can see of the difference in sharpness from reviewers is where the focus was done. On FF, DoF is thinner and it can easily alter sharpness of some of the image areas as long as the lens isn't focused beyond the hyperfocal distance.
07-24-2016, 08:47 AM   #13
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If you want to test a lens, use a tripod and lock up the mirror...
07-24-2016, 09:05 AM   #14
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I vote for motion blur.

1/125, handheld, 28mm and viewing practically a 100% crop with a 36 MP camera, and you are going to see camera shake blur, if not some subject motion blur too. As the D800 Technical Guide emphasizes [PDF 2.5MB]:
"At the high resolutions offered by the D800/D800E [ie 36MP], even the slightest camera shake can result in blur".

Even with Pentax SR enabled.
07-24-2016, 09:10 AM   #15
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Motion blur can be an unintended consequence of increased pixels. Somebody told me that, I didn't think it up myself.
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