Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-11-2014, 07:09 PM   #1
Forum Member




Join Date: Aug 2014
Location: Boston
Posts: 73
K-3 AF-C Focus Problems

I've got a new K-3 and Sigma 70-200mm/f2.8 DG HSM OS lens and I'm trying to take photos of cross-country runners. I've been using the K-7 and DA* 50-135mm for the past 5 years and got comfortable using AF-C and the center focus point to capture the runners. Not every photo was in focus, but I could manage to get enough in focus shots to be satisfied.

I was hoping the K-3 would improve the AF performance, but I'm getting worse performance, not better.

I'm using the following settings:
Av priority, SR off, lens OS off, generally 1/500 or faster.
AF-C, center point, SEL-S (center 9-points)
16. 1st frame action in AF-C - Focus Priority
17. Action in AF-C Continuous - Focus Priority
18 - I've tried AF hold off, low, med and high
I've also tried using shutter-release AF and back-button AF, with little difference.

I can see the center AF point light up on the runner, yet I'm getting entire sequences out of focus. It's not camera shake or slow-shutter - the camera just seems slow to recognize that the runner has moved forward and is no longer in focus. You can see the 3rd shot below is very out of focus, but in the 4th shot the camera has tried to refocus. It is still way behind the runner though.

Here's an example of what I mean:

(all f4, 1/1250, 200mm)

50% close-up:


The focus was on the center of the runner's chest throughout the sequence.

I know the K-3 and the lens can do the job. At 100%, you can count his eyelashes. Here's a crop at 50%:


I've got way too many out-of-focus sequences where the runner is simply ahead of the plane of focus, even when the initial shot is pre-focused on the spot where I want to begin the sequence.

With the K-7, I could prefocus, get 2 or 3 shots in focus, then lose 1 or 2 shots while the camera refocused, then get another 1 or 2 shots in focus. With the K-3, I'm getting complete sequences where the runner is never in good focus at all.

I'd really appreciate any thoughts on settings or technique that can help me out.

09-12-2014, 01:54 AM   #2
Pentaxian




Join Date: Jul 2010
Location: Lyngby, Copenhagen
Photos: Albums
Posts: 742
QuoteOriginally posted by MrNPhoto Quote
I can see the center AF point light up on the runner, yet I'm getting entire sequences out of focus. It's not camera shake or slow-shutter - the camera just seems slow to recognize that the runner has moved forward and is no longer in focus. You can see the 3rd shot below is very out of focus, but in the 4th shot the camera has tried to refocus. It is still way behind the runner though.


[ ... snip ... ]

I'd really appreciate any thoughts on settings or technique that can help me out.
I sometimes have the same experiences. The camera stops driving the lens for 3 shots, then makes a huge leap forward and tries to catch up. I seem to remember the K-5 does the same thing.


Two things to try:
1. Drive mode on Medium speed instead of High. This should in theory give the focus system a little more mirror down time.
2. As you acquire the target in the viewfinder and establish a steady pan, try half-pressing the shutter button for a second or two to give the focus system maximum mirror down time to start a good prediction. Only then mash the shutter button fully and begin shooting.


Regards,
--Anders.
09-12-2014, 02:50 AM   #3
Pentaxian
Tjompen1968's Avatar

Join Date: May 2012
Location: Norrköping, Sweden
Photos: Gallery | Albums
Posts: 1,319
Try using SEL-M and Hold to OFF. I find it to do a much better job in tracking than SEL-S, I think the area is to small. Also it is important to get a focus lock on the center before it starts tracking. In the beginning I got the same result as you and was not happy but now I think that I have figured it out because the results are much better. Shot a running train the other day coming towards me at 80 km/h and I took 6 shots while tracking (back button focusing) and 5 of them in focus.
09-12-2014, 04:52 AM   #4
Forum Member




Join Date: Aug 2014
Location: Boston
Posts: 73
Original Poster
QuoteOriginally posted by Tjompen1968 Quote
Try using SEL-M and Hold to OFF. I find it to do a much better job in tracking than SEL-S, I think the area is to small. Also it is important to get a focus lock on the center before it starts tracking. In the beginning I got the same result as you and was not happy but now I think that I have figured it out because the results are much better. Shot a running train the other day coming towards me at 80 km/h and I took 6 shots while tracking (back button focusing) and 5 of them in focus.
Thanks. I'll try SEL-M and hold to off. I had hold on MED for another race where there were lots of people crossing in front of the runners, and it worked well then (the runners were not coming towards the camera).
I do have focus priority set for initial shot and af-c release, and I do see the center focus point flash red on the middle of the runner, yet the first shot (and subsequent shots) are out-of-focus. I can also see through the viewfinder that the runner is no longer in focus, but the camera hasn't tried to adjust the focus. Then it tries to catch up, but by that time the runner has moved, and it's still out-of-focus.

I thought a single runner coming at an angle to the camera would have been a piece of cake for the K-3 + Sigma 70-200, but frankly I had better results with the K-7. I'm happy to adjust my technique or settings, but I didn't expect it to give me problems with this type of shot.

09-12-2014, 01:07 PM   #5
Pentaxian
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
as a side note, I have noticed that sometimes the focus red dot lights up in the viewfinder making you think it has acquired focus, but on occasion there is no corresponding beep confirmation. This leads me to believe that many of the issues we are experiencing might be related to this (annoying) behavior. When the camera beeps the focus is spot on. But when it doesn't (as it sometimes does randomly) I can pretty much guarantee the image won't be in focus upon close examination.

YMMV

Michael
09-12-2014, 01:31 PM   #6
Site Supporter




Join Date: Sep 2012
Photos: Gallery | Albums
Posts: 1,728
QuoteOriginally posted by MJSfoto1956 Quote
as a side note, I have noticed that sometimes the focus red dot lights up in the viewfinder making you think it has acquired focus, but on occasion there is no corresponding beep confirmation. This leads me to believe that many of the issues we are experiencing might be related to this (annoying) behavior. When the camera beeps the focus is spot on. But when it doesn't (as it sometimes does randomly) I can pretty much guarantee the image won't be in focus upon close examination.

YMMV

Michael
I believe it's the green hexagon in the viewfinder, not the red focus point indicator, that confirms the AF lock.
09-12-2014, 01:43 PM   #7
Loyal Site Supporter
clackers's Avatar

Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 8,663
What happens when you put the DA50-135 on the K-3, MrNPhoto?
09-12-2014, 02:29 PM   #8
Veteran Member
awaldram's Avatar

Join Date: May 2008
Location: Hampshire
Photos: Gallery
Posts: 720
QuoteOriginally posted by IchabodCrane Quote
I believe it's the green hexagon in the viewfinder, not the red focus point indicator, that confirms the AF lock.
Correct

Red indicators show focus point selected not AF status
Hexagon shows AF status
Hand shows SR status

09-12-2014, 02:34 PM   #9
Pentaxian
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
QuoteOriginally posted by IchabodCrane Quote
I believe it's the green hexagon in the viewfinder, not the red focus point indicator, that confirms the AF lock.
Indeed it is, but the core point of the issue remains: most people focus on the red dot and when it stops stops blinking they may "think" it is in focus (and based on the ONLY red light behavior, sometimes it is, sometimes it is not -- take your pick). But you are correct: it is not the red dot that confirms focus it is the combination of the green hex and the beep. In a crowded, noisy environment it is easy to miss the beep. Likewise, in a fast-action environment it is easy to miss the green hex as you eye is literally focused on the framing (and the red dot). I believe that "some" of the focus issues being discussed here may be associated with this phenomenon.

YMMV

Michael
09-12-2014, 04:40 PM   #10
Forum Member




Join Date: Aug 2014
Location: Boston
Posts: 73
Original Poster
QuoteOriginally posted by clackers Quote
What happens when you put the DA50-135 on the K-3, MrNPhoto?
Well, I can't tell you because the DA50-135 SDM failed for the second time. The lens was purchased in 2009, and was repaired for SDM failure in 2010. This summer, it failed again. Also, the weather sealing at the back of the lens came undone. I've sent it to Precision Camera, but haven't heard back from them yet. I'll let you know once the lens is repaired and returned.

---------- Post added 09-12-14 at 07:45 PM ----------

QuoteOriginally posted by MJSfoto1956 Quote
as a side note, I have noticed that sometimes the focus red dot lights up in the viewfinder making you think it has acquired focus, but on occasion there is no corresponding beep confirmation. This leads me to believe that many of the issues we are experiencing might be related to this (annoying) behavior. When the camera beeps the focus is spot on. But when it doesn't (as it sometimes does randomly) I can pretty much guarantee the image won't be in focus upon close examination.

YMMV

Michael
I think you might be right about mistaking the AF point highlight for focus confirmation. I don't think I was looking for the focus hexagon, assuming that since I had set it to focus priority for first frame, it would actually wait for focus lock before taking the first frame. This is clearly not the behavior I'm getting - first frame is out of focus, then the rest of the sequence is out of focus. I'll try again, paying attention to focus lock and the beep before pressing the shutter release.
09-12-2014, 07:34 PM   #11
Site Supporter




Join Date: Sep 2012
Photos: Gallery | Albums
Posts: 1,728
QuoteOriginally posted by MrNPhoto Quote
Well, I can't tell you because the DA50-135 SDM failed for the second time. The lens was purchased in 2009, and was repaired for SDM failure in 2010. This summer, it failed again. Also, the weather sealing at the back of the lens came undone. I've sent it to Precision Camera, but haven't heard back from them yet. I'll let you know once the lens is repaired and returned.

---------- Post added 09-12-14 at 07:45 PM ----------


I think you might be right about mistaking the AF point highlight for focus confirmation. I don't think I was looking for the focus hexagon, assuming that since I had set it to focus priority for first frame, it would actually wait for focus lock before taking the first frame. This is clearly not the behavior I'm getting - first frame is out of focus, then the rest of the sequence is out of focus. I'll try again, paying attention to focus lock and the beep before pressing the shutter release.
I'm the last person here who can claim to be an tracking AF expert but I think if you don't have initial focus lock for the first frame then you won't get any subsequent frame in focus, either. Basically, the camera can't keep something in focus if it never had it in focus to start with. At least that's how I perceive the way it works.
09-12-2014, 09:40 PM   #12
Pentaxian




Join Date: Jun 2009
Location: GMT +10
Photos: Albums
Posts: 10,764
QuoteOriginally posted by MrNPhoto Quote
I'm using the following settings:
Av priority, SR off, lens OS off, generally 1/500 or faster.
AF-C, center point, SEL-S (center 9-points)
16. 1st frame action in AF-C - Focus Priority
17. Action in AF-C Continuous - Focus Priority
18 - I've tried AF hold off, low, med and high
I've also tried using shutter-release AF and back-button AF, with little difference.
My settings for this shoot would be:
- AE metering: multi-segment; (plus make sure AE is not linked to AF point)
- TAV mode, set shutter 1/500 or higher, set aperture f4-5.6
- auto ISO up to ISO 3200, maybe ISO 5000 if lighting is poor
- SR on, lens OS off
- AF-C, high
- Auto (27 points) focus mode
- 1st frame action in AF-C - Release Priority (if you want to start the sequence fast, 'Auto' otherwise)
- Action in AF-C Continuous - Focus Priority (you want the sequence focussed)
- Hold AF status: 'off' (there's no obstacle between the runner and the camera, so 'Hold AF Status' would have nothing to do, and here the camera should always be doing AF).

I always start off an action shoot using Auto 27 point AF enabled because the focus area covered by the K-3 is pretty small and centred to start with (pic below related), and I'm used to being a centre-point shooter with the K-5 and K-x.



Even if I am shooting RAW only, I also make sure I have all lens corrections/digital filters/high-ISO NR etc options disabled. Turning these off seems to make the camera more responsive, because even if you are shooting RAW, those settings may still be used in creating the JPG preview included in the RAW.

For info, the K-3 'Features' page on these advanced AF topics is quite useful.

I also have to ask: were you using a UV or 'protection' filter on the lens? Sometimes they can produce issues with AF.

Last edited by rawr; 09-12-2014 at 09:46 PM.
09-13-2014, 04:53 AM   #13
Loyal Site Supporter
clackers's Avatar

Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 8,663
QuoteOriginally posted by MrNPhoto Quote
Well, I can't tell you because the DA50-135 SDM failed for the second time. The lens was purchased in 2009, and was repaired for SDM failure in 2010. This summer, it failed again.
It's such a beautiful lens (I scored one cheap with SDM busted) that you should just do the screwdrive motor hack and be done with it. :-)

It'll be faster to focus for sports, just not silent.
09-13-2014, 07:28 AM   #14
Forum Member




Join Date: Aug 2014
Location: Boston
Posts: 73
Original Poster
QuoteOriginally posted by clackers Quote
It's such a beautiful lens (I scored one cheap with SDM busted) that you should just do the screwdrive motor hack and be done with it. :-)

It'll be faster to focus for sports, just not silent.
I agree - the DA* 50-135mm is outstanding optically, and gave me excellent results. I am eager to get it back. I did find that for photographing track and field, I could use the extra reach of the 70-200mm, and was expecting it to be faster focusing than the DA50-135m.

---------- Post added 09-13-14 at 10:35 AM ----------

QuoteOriginally posted by IchabodCrane Quote
I'm the last person here who can claim to be an tracking AF expert but I think if you don't have initial focus lock for the first frame then you won't get any subsequent frame in focus, either. Basically, the camera can't keep something in focus if it never had it in focus to start with. At least that's how I perceive the way it works.
So that brings up the question of what setting 16. 1st Frame Action in AF.C actually controls. The manual says that in AF.C mode, "the shutter can be released even if the subject is not in focus." so what is the difference between release priority and focus priority for 16? If I'm able to release the shutter when the subject is not in focus, what difference does 16 make? Setting 17. Action in AF.C Continuous has a default of focus-priority, but again, I'm seeing that that camera is allowing the subject to get out of focus, then trying to refocus, only to be late and missing re-acquiring focus.

---------- Post added 09-13-14 at 10:43 AM ----------

QuoteOriginally posted by rawr Quote
I always start off an action shoot using Auto 27 point AF enabled because the focus area covered by the K-3 is pretty small and centred to start with (pic below related), and I'm used to being a centre-point shooter with the K-5 and K-x.
I may try this, as the focus points are smaller than the K-7 and in this situation, it's not a busy scene with many AF targets.

QuoteOriginally posted by rawr Quote
Even if I am shooting RAW only, I also make sure I have all lens corrections/digital filters/high-ISO NR etc options disabled. Turning these off seems to make the camera more responsive, because even if you are shooting RAW, those settings may still be used in creating the JPG preview included in the RAW.
Yes, all these are disabled, except for highlight correction.

QuoteOriginally posted by rawr Quote
I also have to ask: were you using a UV or 'protection' filter on the lens? Sometimes they can produce issues with AF.
No filter on the lens, and the Sigma comes with a hood extension collar for APS-C sensor cameras, so plenty of flare protection from the deep hood. (Though in my example shots above, the sun was behind me).

Thanks for the suggestions.
09-13-2014, 07:54 AM   #15
Site Supporter




Join Date: Sep 2012
Photos: Gallery | Albums
Posts: 1,728
QuoteOriginally posted by MrNPhoto Quote
So that brings up the question of what setting 16. 1st Frame Action in AF.C actually controls. The manual says that in AF.C mode, "the shutter can be released even if the subject is not in focus." so what is the difference between release priority and focus priority for 16? If I'm able to release the shutter when the subject is not in focus, what difference does 16 make? Setting 17. Action in AF.C Continuous has a default of focus-priority, but again, I'm seeing that that camera is allowing the subject to get out of focus, then trying to refocus, only to be late and missing re-acquiring focus
Here's a suggestion... set #16 to Focus Priority and see what happens. As many more experienced than I have said, there are so many options, often inter-related, with the new AF system that it's nearly impossible to know what the best combination of settings will be without some trial and error.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
action, af, af-c, af.c, beep, behavior, camera, center, confirmation, da50-135, dslr, focus, frame, k-3, k3, lens, pentax k-3, release, runner, sdm, shot, shots, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-3 AF.C questions Lurch Pentax K-3 9 02-05-2015 08:43 PM
K-3's AF.C with Focus priority. skyer Pentax K-3 18 12-11-2014 05:44 PM
How good is the K-3's AF-C tracking AF? Jeff Charles Pentax K-3 6 12-09-2013 03:41 PM
K-3 AF-C Test Picts Winder Pentax K-3 64 11-05-2013 11:09 PM
Pentax K-x: focus confirmation in AF-S, AF-C, not AF-A manteiv Pentax DSLR Discussion 24 12-10-2010 07:25 PM



All times are GMT -7. The time now is 04:14 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top