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12-11-2011, 08:17 AM   #1
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AF problems with the K-r

Just a question, I shot a bunch of pics of a friend's band's show the other night and had a lot of shots that were front focused (using a FA 50 1.4) in that the microphones were all in focus but the faces behind them were not. I was using the center AF point exclusively and was careful to focus on their faces, but would the FF issue be the problem here? The lights were changing very quickly so I can understand if that was throwing things out of whack, but I certainly lost a lot of good shots because of this. (of course, I could have been aiming the AF in the wrong area, that's always a possibility)

Any ideas? There were a few pictures that got the focus just perfect that are to die for, I'd just like to more consistently take that kind of shot.

12-11-2011, 08:47 AM   #2
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Moved from the "K-r discontinued" thread.
12-11-2011, 11:55 AM   #3
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I had the same problem a month of so ago with the K-r regardless of lens severe FF using phase detect AF. The only work around is to use the live view contrast AF, or manual focus. I had lots of shots of microphones that were in focus with fuzzy faces behind them. The lighting was also fairly static

I'm afraid this is pretty much what you get with the K-r using phase detect at concert lighting..very few if any shots are in focus
12-11-2011, 05:48 PM   #4
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From what you describe, this has nothing to do with front focus, but rather the AF system not behaving as you expect. The focus "points" are not discrete points, but larger zones. Larger than the little red indicator you see in the viewfinder. It sounds like the camera was just locking onto the mics, perhaps they had easier edges to grab onto with the unusual lighting.

The easiest way for you to work around this is not to shoot wide open at f/1.4 in these conditions. Stop down a bit to increase the depth of field, and get both the mic and face in focus. Considering that depth of field extends farther behind the focal point than in front, from the DoF you describe, the mics would have been out of focus if the face was nailed. That would likely detract from the shot, too.

12-11-2011, 08:17 PM   #5
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@OP post pics with EXIF info (shutter speed / Iso / aperture / focal length) -the good the bad and the ugly
12-12-2011, 07:48 AM   #6
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jolepp, thanks for moving the thread to the appropriate location. I'll try to link to three representative shots, all of which were shot wide open at 1.4 with auto iso enabled (I think EXIF should still be available, if not I'll post it again.. I've intentionally not done any post processing and just used lightroom's regular export settings, shrunk down to web size. As you can see, the focus is clearly on the microphone in one of the saxophone pictures, but I'm not sure where I would aim my camera to get the face in focus (as that is where I was pointing. Maybe a smaller aperture would have helped, but when shooting live I always try to get as fast of a shutter speed as possible.

Any thoughts?
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Last edited by Tokyohawk; 12-12-2011 at 08:13 AM. Reason: Made a mistake linking picture
12-12-2011, 02:52 PM   #7
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No Exif listed for me. I find the forum snips it when I post images over a particular size. Could just be a Google Chrome thing w/e.

Just my opinion, and hard to say with out the Exif data, the pic above (#3) looks like motion blur - is see a reasonably clear drum set, shoulder and elbow look sharper than eyes, and the Mic in foreground looks focused. The first and second pic the Sax player is definitely in OOF back ground... I wouldn't call it FF, the camera is focused, just not on the target you want IMO. Similarly shooting through trees for birds, using spot focus might be extremely helpful here... you may have used spot focus, but we cant tell with out Exif.

As I posted in other thread - slow shutter speeds will be your bane. Freezing motion of hand, and moving body parts would expect you to be 1/100 or faster - 1/30 s is asking for trouble.
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12-12-2011, 03:55 PM   #8
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Thanks Mattt, I appreciate the insight.

Not sure why the EXIF didn't come through, but just checking my settings here...
Guitar player picture: 1/80 sec at f/1.4, spot metering, spot focus (center), ISO 400. (note, this is one of the pictures that I like)

The other two pictures had the same values except the middle one used IS0 800.
I was pretty up close, so DOF was probably an issue as well.

If I could only get my friends to play without microphones...

12-13-2011, 02:25 AM   #9
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Halogen lights = FF with the K-r. I've noticed also the AF points are far larger than they are indicated in the VF the central point is about the size of the spot metering area. This can cause some problems locking onto subjects you don't want. When I used the K-r to shoot at a concert even making an allowance for this I got microphones in focus and people OOF, ie front focus consistently. Until I switch to live view
12-13-2011, 02:43 AM   #10
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QuoteOriginally posted by Mr Spocko Quote
This can cause some problems locking onto subjects you don't want. When I used the K-r to shoot at a concert even making an allowance for this I got microphones in focus and people OOF, ie front focus consistently.
That isn't front focus. That is missing focus. Front focus would be if the camera locked onto the face behind the mic, and the focus of the mic was nailed. This is why I jumped down your throat the other day, you're conflating other issues with the tungsten thing.

You're right about the size of the center focus "point" though. Each AF point is much larger than the indicator you see in the viewfinder. It takes some practice to make the most of it, and even then mistakes can be made.
12-13-2011, 03:26 AM   #11
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Hmm ... assuming the center AF sensor area is roughly equal to the center circle of the viewfinder (should be?) I'd say #1 is borderline where AF *might* legitimately have locked on the mics, but in #2 the distance from the center to the mics is getting too much of a scretch for that. With #3 it is hard to tell what is in focus without pixel peeping (?). (EXIF would have been useful ...)

Then again AF is not absolutely reliable, that is, it sometimes just misses, so the verdict from #2 alone is more like "could be" than "definitely an example of FF (induced by artificial light)". Otoh, if the results are consistently like #2 when you use center point only and anything closer to you has been clear of the center circle when you locked focus (half pressed the shutter, got confirmation) it would seem that you have PDAF front focusing on you, probable cause for it being (low) artificial (tungsten/halogen) light. To be reasonably sure of having FF (in tungsten light) (or not) you'd need to set up something static where other potential explanations for FF can be ruled out ("beyond reasonable doubt" ). (some ideas: https://www.pentaxforums.com/forums/pentax-k-5-forum/129738-k-5-user-auto-foc...t-results.html)

Last edited by jolepp; 12-13-2011 at 03:34 AM.
12-13-2011, 04:39 AM   #12
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Shot 2 is def an example of front focus. There are times when you could have had the AF lock onto something else (say a higher contrast subject) when I was taking shots I made a serious effort to competely avoid that chance even trying to lock AF to the side of faces etc. My efforts did not work very well so I had a choice of lots of FF shots, or to use MF and live view.

Whilst the bigger AF point should be something to make users aware of it's still not going to help with the FF. IMO the K-r is almost unusable in this light for phase detect AF
12-18-2011, 11:54 AM   #13
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It is most definitely NOT front focus, but a simple case of the camera rnot reading your mind and realizing you wanted the person standing *behind* the microphone rather than the microphone to be in foca. It,s just a fact of life with concert shooting - cameras will tend to focus on mics, stands, and instruments, rather than people. That's why I so often switch to manual focus even with my AF lenses. But FWIW, aiming at their torso or legs is sometimes a way to get the AF system to not focus on someing that is in front of their face.
12-18-2011, 02:58 PM   #14
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I disagree esp shooting with a K-r in similar lighting while the first and third shots might be borderline if the OP is using the central AF point the second shot is highly unlikely to be user error. The mic is nowhere near the AF sensor if the Op's on central AF point. I'm sure he'll fill us in on this.

Last time I tried the K-r in this light it didn't matter where you put the AF points it hit almost nothing! The exception seems to be if there is very high contrast, which normally there is not.
Yes the AF points being so large is also a problem but there are other issues too
12-18-2011, 03:09 PM   #15
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You have no idea where OP pointed his focus point before recomposing the shot, as is normal to do, and you're still conflating other issues with this tungsten ff bug. Focus hunting (or failing) in low light is not ff. Missing focus by locking onto the wrong element in your scene is not ff.

Y'know, I took a glance and 22 of your 25 posts on this board are complaining about tungsten ff. We get it, you're pissed off. You don't need to spam it in every topic, especially after returning the camera.
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