Pentax K-3II and Sigma 17-70mm AF issues?

12345 · 01-12-2022, 06:25 PM

I've been a happy Pentax user for many years now, and recently acquired a K-3II to replace my aging K-5II. I love the new camera, (had to get used to the different back-button AF location though), but there's one problem that kinda bugs me....

My K-5II and my Sigma 17-70 f/2.8-4 HSM Macro lens got along wonderfully; photos were tack sharp, AF was snappy, etc... I expected if anything that my new K-3II would do even better, seeing as it has improved AF from the K-5 series. However, that doesn't seem to be the case. I shot a wedding with the K-3II and Sigma combo shortly after acquiring my new camera, and was quite disappointed that a rather high percentage of the shots turned out slightly out-of-focus!

I've noticed since then as well that the K-3II and 17-70mm combo just struggles to lock focus. Often it'll "focus" but when I enlarge the photo I see that it's slightly OOF. That's not to say that it's incapable of focusing. Some shots are spot on! But there are enough that aren't that it rather concerns me!

Any ideas what could be the problem, and what I can do to fix it? I have another potential wedding gig coming up, and I'd like to be more confident in my camera.
Thanks in advance!

**jumbleview** · 01-12-2022, 06:37 PM

Is OOF consistent? In other words is it always back focus or front focus? Did you try Auto Focus Fine Adjustment.

stevebrot · 01-12-2022, 09:40 PM

Originally posted by 12345

However, that doesn't seem to be the case. I shot a wedding with the K-3II and Sigma combo shortly after acquiring my new camera, and was quite disappointed that a rather high percentage of the shots turned out slightly out-of-focus!

Is this the same used lens that was found to have a non-functional zoom ring shortly after purchase?
Sigma 17-70mm broken zoom ring? - PentaxForums.com.

Is it being used with OS turned on or off? How are your battery levels when this happens?

How is your previously owned K-3II with other lenses. (A possible cause might be a PDAF sensor mirror and/or sensor that needs cleaning.)

Steve

12345 · 01-13-2022, 11:50 AM

Originally posted by stevebrot

Is this the same used lens that was found to have a non-functional zoom ring shortly after purchase?
Sigma 17-70mm broken zoom ring? - PentaxForums.com.

No, I had forgotten about that one!

This is the 17-70mm f/2.8-4 HSM version that I've had for years. It's a non OS version. I usually keep my battery close to full, but I haven't noticed any differences whether the battery was fully charged or low.

Good question about other lenses... I don't recall any particular issues with other lenses. I've used my 400mm and 50mm several times with it, and didn't notice anything particularly strange, but that only represents probably 5-10% of real-life usage, so I might have overlooked something. My 17-70mm is on the camera 90% of the time.

12345 · 01-13-2022, 11:51 AM

Originally posted by jumbleview

Is OOF consistent? In other words is it always back focus or front focus? Did you try Auto Focus Fine Adjustment.

That's a good question, and one that I began to think of as I made this post.

I'll have to do some more "scientific" testing, and see if I can identify any patterns.
Thanks!

12345 · 01-13-2022, 12:10 PM

I just used pulled up LR and filtered all images by K-3II and 17-70mm lens. Based on a quick evaluation, I'd say it's definitely a front-focus issue. Every time the photo is blurred, the background is even more blurry, which leads me to believe that it was focusing slightly in front of the subject. Next to use a tripod and focus chart to double-check...

01-12-2022, 06:25 PM	#1
12345 Veteran Member Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 520	Pentax K-3II and Sigma 17-70mm AF issues? I've been a happy Pentax user for many years now, and recently acquired a K-3II to replace my aging K-5II. I love the new camera, (had to get used to the different back-button AF location though), but there's one problem that kinda bugs me.... My K-5II and my Sigma 17-70 f/2.8-4 HSM Macro lens got along wonderfully; photos were tack sharp, AF was snappy, etc... I expected if anything that my new K-3II would do even better, seeing as it has improved AF from the K-5 series. However, that doesn't seem to be the case. I shot a wedding with the K-3II and Sigma combo shortly after acquiring my new camera, and was quite disappointed that a rather high percentage of the shots turned out slightly out-of-focus! I've noticed since then as well that the K-3II and 17-70mm combo just struggles to lock focus. Often it'll "focus" but when I enlarge the photo I see that it's slightly OOF. That's not to say that it's incapable of focusing. Some shots are spot on! But there are enough that aren't that it rather concerns me! Any ideas what could be the problem, and what I can do to fix it? I have another potential wedding gig coming up, and I'd like to be more confident in my camera. Thanks in advance!

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01-12-2022, 06:37 PM	#2
jumbleview Site Supporter Join Date: May 2012 Location: Concord, CA Posts: 1,069	Is OOF consistent? In other words is it always back focus or front focus? Did you try Auto Focus Fine Adjustment.

01-12-2022, 09:40 PM	#3
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by 12345 However, that doesn't seem to be the case. I shot a wedding with the K-3II and Sigma combo shortly after acquiring my new camera, and was quite disappointed that a rather high percentage of the shots turned out slightly out-of-focus! Is this the same used lens that was found to have a non-functional zoom ring shortly after purchase? Sigma 17-70mm broken zoom ring? - PentaxForums.com. Is it being used with OS turned on or off? How are your battery levels when this happens? How is your previously owned K-3II with other lenses. (A possible cause might be a PDAF sensor mirror and/or sensor that needs cleaning.) Steve

01-13-2022, 11:50 AM	#4
12345 Veteran Member Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 520 Original Poster	Originally posted by stevebrot Is this the same used lens that was found to have a non-functional zoom ring shortly after purchase? Sigma 17-70mm broken zoom ring? - PentaxForums.com. No, I had forgotten about that one! This is the 17-70mm f/2.8-4 HSM version that I've had for years. It's a non OS version. I usually keep my battery close to full, but I haven't noticed any differences whether the battery was fully charged or low. Good question about other lenses... I don't recall any particular issues with other lenses. I've used my 400mm and 50mm several times with it, and didn't notice anything particularly strange, but that only represents probably 5-10% of real-life usage, so I might have overlooked something. My 17-70mm is on the camera 90% of the time.

01-13-2022, 11:51 AM	#5
12345 Veteran Member Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 520 Original Poster	Originally posted by jumbleview Is OOF consistent? In other words is it always back focus or front focus? Did you try Auto Focus Fine Adjustment. That's a good question, and one that I began to think of as I made this post. I'll have to do some more "scientific" testing, and see if I can identify any patterns. Thanks!

01-13-2022, 12:10 PM	#6
12345 Veteran Member Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 520 Original Poster	I just used pulled up LR and filtered all images by K-3II and 17-70mm lens. Based on a quick evaluation, I'd say it's definitely a front-focus issue. Every time the photo is blurred, the background is even more blurry, which leads me to believe that it was focusing slightly in front of the subject. Next to use a tripod and focus chart to double-check...