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10-17-2019, 06:31 PM   #1
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SMC Pentax-DA 16-45mm F4 with K3 - focus seems to fall off

I bought my 16-45 lens as part of my starting kit when I picked up my K10D back in 2007. It was my only lens for quite a while, and (up until recently) I've been happy with the results. Mostly I shoot landscapes/wildlife, but about once or twice a year I do get a call to take photos of people in some capacity (portraits or events)

This past September I took a group photo for an event at my daughter's school. It had to be outside in available light, and I needed a fast shutter speed as it was a group of 130 people, so I shot at ISO1600, 1/320 at f7.1 zoomed out to 18mm. It looked decently in focus on the LCD... then at home in Lightroom I noticed that the focus seems to fall off on the edges.

In another "forced to use evening available light" setting, I photographed a group of 30 people at 1/50 sec f/4, ISO800 16mm and again, the focus falls off on the edges. I was trying to avoid increasing the ISO because I thought that was the source of the blurryness in the first group shots, but as the light decreased I increased the ISO and the blurry effect seems to be pretty much the same.

The pictures are OK for phone viewing or printing 4x6 or 8x10, however zooming in showcases the aberration.

After the second group event, I thought maybe it was a problem with low light, maybe I needed a smaller f/stop to find an optimal focal point for the lens, however I tested it in the daylight and I can still see the aberration even shooting at f/8 at ISO400 in bright sun.

That brought me to this forum, and I've been reading through the mixed reviews of this lens on the reviews page. Some people say it is sharp edge to edge, some people are describing the same aberration I'm experiencing.
I then realized, I've changed camera bodies twice since purchasing this lens... K10D to K5 and now I shoot K3. Also, when I got the K3 I was also given a 31mm prime lens for Christmas, and I've been pretty much shooting all my landscapes with that lens... so I haven't been using the 16-45 outside of occasionally needing the wide angle for group shots.

I'm wondering... is it possible this lens is not good with the new K3? If so, why would that be? Has anyone else noticed something similar?

---------- Post added 10-17-19 at 06:38 PM ----------

OH and to add to this... the shots that I did in the same light at 22mm do not have this focus flaw, it's just the ones that are zoomed out to the maximum.

10-17-2019, 06:55 PM   #2
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QuoteOriginally posted by jadeddo Quote
I'm wondering... is it possible this lens is not good with the new K3? If so, why would that be? Has anyone else noticed something similar?
It is possible that the extra pixels are exposing weakness at the wide end that were not obvious before. I suspect that if you downsample in post processing to 16Mpx, the results will look essentially the same as what you got with the K-5.


Steve

(...had to retire my DA 18-55/3.5-5.6 when I got the K-3...)
10-17-2019, 07:13 PM   #3
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If I recall the 16-45 also suffers from barrel sag sometimes. Check yours at 16mm and see if it is wobbly. The lens seems more variable than most.
10-17-2019, 07:38 PM   #4
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QuoteOriginally posted by UncleVanya Quote
If I recall the 16-45 also suffers from barrel sag sometimes. Check yours at 16mm and see if it is wobbly. The lens seems more variable than most.
This. I've seen reviews of this lens where the owner sent it in because the pictures started to look soft, and after adjusting and I guess tightening internals, the lens was as good as it was when newer. Mine has the wobble and it does seem to affect the wider focal lengths a bit.

10-17-2019, 07:43 PM   #5
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QuoteOriginally posted by stevebrot Quote
It is possible that the extra pixels are exposing weakness at the wide end that were not obvious before. I suspect that if you downsample in post processing to 16Mpx, the results will look essentially the same as what you got with the K-5.


Steve

(...had to retire my DA 18-55/3.5-5.6 when I got the K-3...)
The reason I'm researching this is because I was wondering if I need to replace it or retire it. I really don't want to shoot with a lens if I have to reduce the image size in order for the image to look good.

---------- Post added 10-17-19 at 07:55 PM ----------

QuoteOriginally posted by UncleVanya Quote
If I recall the 16-45 also suffers from barrel sag sometimes. Check yours at 16mm and see if it is wobbly. The lens seems more variable than most.
I'm not sure how much sag there needs to be for it to require repair... it definitely feels a little wiggly when it is out all the way. I never really paid close attention to it before, but my 50-135 doesn't extend out when it zooms, whereas the 16-45 doubles in length. Maybe it is just worn out after 12 years of being lugged around.
10-17-2019, 11:55 PM   #6
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Apart from the possible impact of lens barrel wobble, I wouldn't be surprised if what you're finding is also an indication of field curvature.

I'm lacking practical experience with the DA16-45, and I don't recall any express mention of field curvature in reviews of this lens, but it's not a thing unheard of in zoom lenses of its kind. (If I remember rightly, the Tamron SP AF 17-50mm F2.8 XR Di II LD Aspherical [IF] shows a considerable amount of field curvature at the short end.)

Does the sharpness drop towards the edges become less severe if you deliberately focus a little more "into" the scene? (That should be a way to test.) But then again, if this was a major issue, you would have probably noticed it earlier, and independent of the camera body used.
10-18-2019, 12:57 AM   #7
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I used a 16-45 (which I still have) with my K-5 (which I no longer have) and the two matched well. There was barrel wobble for sure but it never seemed to make a huge difference. If there was edge distortion because of the wide angle of view - which there was - it was a worthwhile trade-off for the wide view; those extra 2mm made a difference from the kit lens.

Whatís interesting is the shift from the 16MP K-5 to the 24MP K-3 where as noted above, the latterís higher resolution would tend to show up defects more clearly. The reverse is also true because I bought my 20-40 in mid-2015 before our California road trip and while it was an improvement over the 16-45 in many ways, I wasnít blown away by the difference on the K-5. On the K-3II however, which I got in 2016 it was clearly better, the extra resolution allowing it to shine. I havenít gone back to the 16-45 on the K-3II but I suspect that it would show up the defects as noted.

10-18-2019, 10:05 AM   #8
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QuoteOriginally posted by Madaboutpix Quote
Apart from the possible impact of lens barrel wobble, I wouldn't be surprised if what you're finding is also an indication of field curvature.

I'm lacking practical experience with the DA16-45, and I don't recall any express mention of field curvature in reviews of this lens, but it's not a thing unheard of in zoom lenses of its kind. (If I remember rightly, the Tamron SP AF 17-50mm F2.8 XR Di II LD Aspherical [IF] shows a considerable amount of field curvature at the short end.)

Does the sharpness drop towards the edges become less severe if you deliberately focus a little more "into" the scene? (That should be a way to test.) But then again, if this was a major issue, you would have probably noticed it earlier, and independent of the camera body used.
I'm pretty sure some of it is field curvature, and I think it has been there before, but I didn't care too much about it because my subjects are usually landscapes. It was only when I needed to shoot a group of people that I paid that close of attention to the edges. My growing suspicion is that this is a situation of people's faces + shooting on my K3 that has brought this to light.

My next test will be to take a shot at each f/stop to see if that helps improve the edges.

For what it's worth... a friend of mine was also shooting the group - she has a full frame Canon and she rented a high end wide lens to shoot. Her shots came out much sharper with less grain (as would be expected) and at first I thought my lens was entirely busted. However, she shot super wide and cropped in, and when I look at her original RAW files I can see a similar focal loss on the edges because of the shallow depth of field. She just cropped the aberrations out. It was after I noticed that when I started thinking it might just be inherent to wide angle zooms. I still want to figure this out, because I like to know WHY things work the way they do, but I also think that a prime lens is going to yield better results than a zoom.

---------- Post added 10-18-19 at 10:17 AM ----------

QuoteOriginally posted by microlight Quote
I used a 16-45 (which I still have) with my K-5 (which I no longer have) and the two matched well. There was barrel wobble for sure but it never seemed to make a huge difference. If there was edge distortion because of the wide angle of view - which there was - it was a worthwhile trade-off for the wide view; those extra 2mm made a difference from the kit lens.

Whatís interesting is the shift from the 16MP K-5 to the 24MP K-3 where as noted above, the latterís higher resolution would tend to show up defects more clearly. The reverse is also true because I bought my 20-40 in mid-2015 before our California road trip and while it was an improvement over the 16-45 in many ways, I wasnít blown away by the difference on the K-5. On the K-3II however, which I got in 2016 it was clearly better, the extra resolution allowing it to shine. I havenít gone back to the 16-45 on the K-3II but I suspect that it would show up the defects as noted.
I've been looking at the 20-40 as a possible replacement, and I've seen some mixed reviews on it but I wonder if that has to do with the camera bodies they are shooting on. Some of the reviews don't mention the camera, and it didn't dawn on me until this week that the camera body could make that much of a difference. (My brain still thinks in film, the 35mm opening is a 35mm opening... vs. DSLRs with higher capacity sensors)
My primary hesitations are that my 16-45 is really good if I stay between 20-45, and in that regard I already have a 20-40. Plus, I have the 31mm prime, and I have consistently used that over my zoom on landscapes. If it turns out that the edges are just going to have this aberration, I can keep that in mind when I shoot, frame the image wider and crop in when I edit. If a lower f/stop helps as well, then that might be the solution for the rare wide-angle situations.
10-18-2019, 10:38 AM   #9
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While prime lenses do often show better corner-to-corner sharpness, this is not necessarily and always the case, particularly in the wide-angle department. For example, among the DA Limiteds (beautifully-rendering lenses, all of them) both the DA15 and the DA20-40 are somewhat notorious for pronounced field curvature. One is a compact prime lens, one is a zoom. Good copies of the DFA15-30 and the DA*11-18, of which particularly the latter may be of interest to you as an APS-C shooter, are known to deliver an amazingly consistent sharpness across the frame that would have been thought impossible ten, fifteen years ago.
10-18-2019, 10:43 AM   #10
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If you want ultrawide I suggest you look on the forum. There is a 10-20 sigma for sale that looks like it would fit the need and while I can't comment on the price - you should look for yourself. The other option is the Pentax 12-24 f/4. Not as sexy as the new 11-18 but much much cheaper and very good.
10-18-2019, 11:30 AM   #11
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QuoteOriginally posted by Madaboutpix Quote
Apart from the possible impact of lens barrel wobble, I wouldn't be surprised if what you're finding is also an indication of field curvature.
That was my thought, though I did not say it explicitly. It is not unusual for field curvature to be essentially undetectable under critical evaluation* of a lower resolution capture (say 16 Mpx), but be much more obvious at 24 Mpx.


Steve

* Meaning 1:1 full resolution (I don't like the term "pixel peeping"). The higher the pixel density, the greater the magnification to display 1:1, hence the enhanced ability to detect missed focus and field curvature. Unless displaying large, the field curvature may not be much of a problem. FWIW, a drop in edge/border sharpness was noted with the DA 16-45/4 at 16mm and f/4 on the K10D (10 Mpx) by Klause at OpticalLimits back in 2007. I would imaging such is more obvious with today's cameras.
10-18-2019, 01:03 PM   #12
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I popped outside this morning and ran an f/stop test with the lens out to 16. It's not a perfect test (I really need a bright sunshine day for that, and here in the PNW we're enjoying Nature's Soft Box cloud cover) As I dropped the f/stop my shutter speed increased, and by the time I got to f/22 I was out at 1/13 of a second. I don't have time to break out my tripod right now, and it is windy anyway so there's going to be background movement at that speed no matter what, HOWEVER, my shutter speeds were fast enough in the middle to avoid camera shake, and I can see a very visible improvement on edge sharpness right at f/11. It's still not *perfect*, but it is definitely noticeable.

So I feel the lens is still quite usable on the K3, but if I'm going to go wide, I should keep the f/stop in mind for improved sharpness at the edges.

Thank you EVERYONE for all your input!
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