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02-02-2014, 10:07 AM - 1 Like   #1
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Compare Notes? - K3 AF wierdness (cont.)

Hi all,

First, this is not a thread about blurry photos, its a thread about mis-focused photos. There was a previous thread that outlined another user's experience entitled "K3 AF Weirdness".

The Issue:
I would like to compare notes with you. I have a K3 (latest firmware) using various lenses (FA31, DA 20-40, 50-135). Its strange, but I have been feeling like an unusually large number of shots have been mis-focused where I know I properly selected the AF point. At narrower apertures, it could be misunderstood as blurry, but wide apertures (i.e., 2.0) tell the story well. For clarity, I am shooting raw in manual mode, minimum 1/180 of a sec, on and off tripod, single user-selected AF point.

My initial attempted solution:
When I first noticed the issue, I decided that perhaps the lenses needed alignment, so I used focus-tune and lensalign to determine the correct AFA position. When I printed the focus-tune reports, it was very clear that many shots were "way" off base. For example, in focus-tune, a perfect shot will have a reported focus value of 0. Lets say that I set the AFA in the camera to -3 and I shoot a series of photos. While most will have a reported focus value in the same range (for example, 100, 110, 90), I was getting a large number of shots that fell out of that general range (for example, 275, -100). Since I shot a large number in the series for each AFA camera setting, I threw out the outliers and determined the correct AFA camera setting with those that were remaining (for most lenses, an AFA setting of -1 or -2 worked). The results.....Stunning sharpness, except for those photos that are mis-focused. In other words, the more frequent appearance of "outliers" were impacting the photos I take in real life.

Real life impact example:
Shooting a person (from directly in front of them and at floor level), whom is resting their head on their crossed arms (they are laying down parallel to my position such that it is effectively like a head and shoulder framed shot). Focusing the single AF point on the eye, some shots have the eye in focus, others have their elbow (a few inches closer than their eye) in focus. To be clear, I am shooting at an aperture of 2.0 to to 2.4 which has a limited DOF field. Thus the problem is easy to detect because accurate focus is critical under these circumstances.

My ask:
Tell me your experiences. I have to decide whether to send the camera back for a replacement. I think the K3 is the most solid and sophisticated APC camera out there. I have been on the fence about switching after 7 years with Pentax. I want to stay. However, this is not helping

02-02-2014, 12:12 PM   #2
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I find that generally the K3 focuses on what I point it at. That being said, a few suggestions before sending it back:

The center point focus fills the space between the arcs you see in the viewfinder. I noticed when I was setting mine up that the viewfinder and the actual center point were not the same. You can check this in live view; set up on a tripod, aim at something clearly defined with the viewfinder, then hit the live view button to see where the center is. If it is off and what you are focusing on lands on the real boundary of the focus point, that may be the cause. What to do from there is up to you; I just mentally adjust. I tend to send my gear in for cleaning and adjustments every so often, and I'll ask them to fix that for me, but in the mean time it is fine.

Once that is out of the way, I would do a simple test. Tripod, focus repeatedly on something, and see if it is repeatable. If not, I'd suggest getting a replacement.

If everything hardware wise seems ok, then look very closely at your technique. I've described the focus mechanism on the K-3 as accurate but not prescient. It tends to focus on what you point it at. That can be good or bad
02-02-2014, 12:35 PM   #3
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QuoteOriginally posted by loganross Quote
Hi all,

First, this is not a thread about blurry photos, its a thread about mis-focused photos. There was a previous thread that outlined another user's experience entitled "K3 AF Weirdness".

The Issue:
I would like to compare notes with you. I have a K3 (latest firmware) using various lenses (FA31, DA 20-40, 50-135). Its strange, but I have been feeling like an unusually large number of shots have been mis-focused where I know I properly selected the AF point. At narrower apertures, it could be misunderstood as blurry, but wide apertures (i.e., 2.0) tell the story well. For clarity, I am shooting raw in manual mode, minimum 1/180 of a sec, on and off tripod, single user-selected AF point.

My initial attempted solution:
When I first noticed the issue, I decided that perhaps the lenses needed alignment, so I used focus-tune and lensalign to determine the correct AFA position. When I printed the focus-tune reports, it was very clear that many shots were "way" off base. For example, in focus-tune, a perfect shot will have a reported focus value of 0. Lets say that I set the AFA in the camera to -3 and I shoot a series of photos. While most will have a reported focus value in the same range (for example, 100, 110, 90), I was getting a large number of shots that fell out of that general range (for example, 275, -100). Since I shot a large number in the series for each AFA camera setting, I threw out the outliers and determined the correct AFA camera setting with those that were remaining (for most lenses, an AFA setting of -1 or -2 worked). The results.....Stunning sharpness, except for those photos that are mis-focused. In other words, the more frequent appearance of "outliers" were impacting the photos I take in real life.

Real life impact example:
Shooting a person (from directly in front of them and at floor level), whom is resting their head on their crossed arms (they are laying down parallel to my position such that it is effectively like a head and shoulder framed shot). Focusing the single AF point on the eye, some shots have the eye in focus, others have their elbow (a few inches closer than their eye) in focus. To be clear, I am shooting at an aperture of 2.0 to to 2.4 which has a limited DOF field. Thus the problem is easy to detect because accurate focus is critical under these circumstances.

My ask:
Tell me your experiences. I have to decide whether to send the camera back for a replacement. I think the K3 is the most solid and sophisticated APC camera out there. I have been on the fence about switching after 7 years with Pentax. I want to stay. However, this is not helping
Could the problem be that you are using AF-A. Ed, at Photouniverse suggested in one of his videos (sorry, I cant recall which one specifically) that in AF-A the camera can get confused and may choose AF-C when AF-S would be more appropriate. That could explain why the focus shifted from your subjects eye to elbow. Setting to AF-S could be more reliable in most cases unless you're shooting action. I've only had my K3 for a short time and I almost always use AF-S so I have not experienced this.
02-02-2014, 12:40 PM   #4
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Thanks guys. The issue persists whether I select center point or another point. The lensalign method, is fairly scientific when followed carefully and my results are pretty inconsistent. I am in AFS mode...I should have mentioned this in my original note.



It seems to me, I have to exchange it.

02-02-2014, 01:15 PM   #5
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That is a pity. Sorry I cant think of any thing else. I misunderstood what you meant by AFA settings. I'm not familiar with Lensalign or focus compensation in general. I'm fortunate in that I can honestly say I have rarely had focusing issues unrelated to user error. My Tamron 70-200 doesn't focus well in live view, that's about it.
02-02-2014, 02:08 PM   #6
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Nikons are known to focus differently in incandescent light than daylight. Could this be (part of) the issue?

M
02-02-2014, 02:21 PM   #7
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QuoteOriginally posted by MJSfoto1956 Quote
Nikons are known to focus differently in incandescent light than daylight. Could this be (part of) the issue?
The K-5 was noted to suffer from this. (Perhaps the K20D too?) I believe it was corrected in the K-5II & later.

Dan.
02-02-2014, 06:13 PM   #8
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Perhaps do some more testing to figure this out.

As an idea, can I suggest that you set up half a dozen decent focus targets you can use to test shooting with 'Select' AF point mode. Maybe use a bunch of small pieces of white cardboard 4-6 inches wide with thick solid black crosses on them (or use those target discs you see on crash test vehicles ) as your focus targets. Set them up at different distances from the camera in a close pattern, but using the sort of general subject distance you normally work with. Then see how accurately you can AF on each target within the group by pointing specific focus points at each target using 'Select' AF point mode. Use only one lens, only AF-S, avoid tungsten light, and make sure you have your AF set to focus (not release) priority. And place the targets within the area actually covered by the AF points, of course:



Then evaluate how accurately the selected AF point is able to lock onto each target. Also see what happens if you use different focus modes (AF-S, AF-C), as well as Auto - 27 points and Zone Select - 9 points (this may help reveal some AF logic).

02-02-2014, 08:46 PM   #9
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Try using a flat target.


Steve
02-03-2014, 07:54 AM - 1 Like   #10
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Hi everyone. I am the person who wrote the 'K3 AF Weirdness' post referenced above, and to a 'T' the issues I had are the ones that loganross(and hello to you!) is having. I elected to replace the orig. K3 as it got no better after the new firmware was installed. The replacement camera is a whole 'nother animal! It acts and AF's just like it should and expect. The difference is like night and day. BTW, there are a few posts over at DP Review describing this same issue, but it looks like there are certainly less than 10 K3's in total that I have found on the net with the issue, and might be as low as five bodies, so it certainly is not a wide spread issue. I would hazard the opinion that a replacement will be perfect for you. Feel free to contact me if you need any more info, and good luck!

David
02-28-2014, 08:51 PM   #11
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Original Poster
David,
Thank you for your reply. I tried a second body and had the same issues. While this wasn't the main driver (I focus on the "where I am going" rather than the "why I am leaving"), I have switched to Fuji (now shooting the X-T1 camera and fast primes). Every camera system has its issues, but I have many wonderful photos from my 7 years shooting pentax
03-01-2014, 08:07 PM   #12
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I too had the exact same behavior. 20% of the shots were in focus, 20% front focused. 60% back focused. No matter what INDIVIDUAL micro adjust I used. However, the minute I specified a GLOBAL setting of +10 then suddenly all my shots are "in focus" now. I believe that once the AF unit is beyond a certain adjustment threshold (from the factory) then the system begins to behave erratically. In my case, setting things globally "moved" the unit back into the sweet spot and the system now behaves "as the engineers designed it". Give it a try. You have nothing to lose.

Michael
05-26-2014, 07:23 AM   #13
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Unfortunately our current K3 started the AF weirdness after the latest firmware update a month or so ago, just like the first one did out of the box. it has rendered the camera unreliable so it is going in to CRIS for a look. For specifics read here if interested: https://www.pentaxforums.com/forums/172-pentax-k-3/263409-second-k3-stops-foc...correctly.html

David
05-26-2014, 08:38 AM   #14
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Just to be sure: What settings do you use: AF-S + Sel 1 or?
05-26-2014, 08:43 AM   #15
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I used AFS, spot center AF. Honestly it has been on that setting since I got it and it worked fine. Then this weirdness started up with inconsistant AF and the micro setting I put into each lens no longer valid and in fact they are really off if I could use them at all. That was why I did a full reset to see if that helped but no.
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