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02-03-2016, 12:41 PM   #1
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Autofocus Problem K3 + 1.4x + 150-450

I'm suddenly having autofocus problems. It is most likely to happen when I'm trying to shoot birds in flight at the shore. This morning, for example, a Northern Gannet flew by as I was standing on the jetty at Allenhurst, NJ. I was pointing directly at the bird (as can been seen by the position in the frame of the smudge against the light background) yet the camera (K3) would not focus with the 1.4x HD and 150-450 lens. This seems to be a new phenomenon that has just started happening in the last couple of weeks. The lens shifts all the way to the short end of the range and refuses to shift even if I then point at something only a few feet away.

The problem was also happening when I tried to grab some photos of Sanderlings on the beach. If I was pointing at the featureless beach the AF would go to the 6 feet setting and stick there. I found that if I pointed to the ground a short way in front of me, I could then get the AF to work by slowly tilting the camera away from me so that the distance slowly increased.

Thinking that perhaps the 1.4x HD was affecting things, I removed it and still had the problem, so it's either the camera or the lens (or some weirdness about the combination).

This afternoon, I went back to Allenhurst with my Sigma 150-500 instead of the 150-450. And the behavior was similar in that if I failed to point directly at the bird, the focus would go to the short end of the range, but it didn't get stuck there like the 150-450. I have taken upwards of 70,000 images with my K-3, so perhaps it's just exhibiting old age, but my sense is that this is more of a lens problem than a camera problem.

Settings:
K-3 camera
TAv mode
AF active area: Spot ( I experimented with the 9-spots setting but it made no difference)
Menu C3 15-18 are all set to 1.
I had the AF button set to AF1 which should allow either the shutter release or the AF button to be used for focusing. I had basically forgotten that I had done this, so possibly this is the problem.

Lens
1.4x HD installed
Preset button set to AF
Focus range set to Full
Mode button set to QFS/A

I just tried some experiments with the AF button switched off and it was fairly easy to reproduce the problem by pointing at some of the remaining snow banks. Hmm: I should try that with the Sigma, too. Same problem.

I'm starting to suspect it's the camera showing its age or perhaps I'm just expecting too much.

Is anyone else seeing anything like this?

Can anyone suggest a remedy? Or some experiments to perform to narrow down the cause of the problem?

Thanks,

Dave

02-03-2016, 01:29 PM   #2
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This could have something to do with the camera's age. I would check to see if the mirror and mirror box are clean and free of dust, as you want to be sure the AF sensor (which basically sits behind 2 mirrors) has a clear view of the scene.

I also would try using all 27 AF points. Since the 150-450mm is in the F6.7 to F8 range with the TC, you're pushing the limits of the AF system and might not get the best results with a single AF point unless you're in bright daylight.

Adam
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02-03-2016, 10:17 PM   #3
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QuoteOriginally posted by davesofnj Quote
And the behavior was similar in that if I failed to point directly at the bird, the focus would go to the short end of the range
That's what my K-3 does with HD TC + DA300 and AFC 27 points, unless when pre-focused and there is a lot of contrast between the subject and the background, otherwise, the camera does a full AF trip from infinity to nearest focus distance and get stuck there. With spot AF or 9 points AF, auto-focus works. So, it is not the same issue as your , but the common point is that the camera AF algorithm get stuck at nearest focus distance. Well, to check you AF module, you could manually focus and check if you get focus confirmation (green indicator) or not. Same thing with live view. And take a few shots, try DoF preview optical to check if the lens aperture is not stuck during AF operation. Try with different lenses with/without TC. Send the whole thing (camera+lens) for repair.

Last edited by biz-engineer; 02-03-2016 at 10:23 PM.
02-04-2016, 08:49 AM   #4
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Thanks for the feedback and suggestions. I have some more data points having again gone to Allenhurst this morning.

1. I decided to take the 1.4x out of the equation by shooting without it.

2. I switched the lens to the 6m - ∞ setting (since my main interest was birds in flight).

3. I switched to 27 AF points as you suggested.

As for dust, I've been running the dust removal action on startup since I acquired the camera. I ran it a few extra times this morning. I'm a bit reluctant to actually poke around inside the camera.

The bottom line is that although things seemed a bit better, I still have the problem.

So, I tried an experiment:

1. I changed the lens back to full focusing range.

2. I switched off the camera and manually adjusted the focus ring to the 6.6 feet end.

3. I pointed the camera at some rocks about 40 yards away and held the shutter half down. It focused correctly and quickly.

4. Without turning the camera off, I manually adjusted the focus ring again to the 6.6 feet end.

5. I pointed at the same rocks. It would not focus. Would not move from the 6.6 feet setting.

When I got home, I repeated the experiment using some trees a hundred yards from our front steps. Same result.

So, I tried the lens with my wife's K-x using the same experiment with the same trees. And the lens worked with the K-x.

So, it looks like the camera is the problem.

I think I need to look into repair services in the New Jersey area.

Dave

---------- Post added 02-04-2016 at 10:56 AM ----------

biz-engineer: I've just seen your reply. Sorry to hear you also have a similar problem.

I'll see what happens with my DA-300.

Wow! Looks like we do have the same problem. With the TC & DA-300, the K-3 won't focus with 27 points selected but worked like a charm with single point.

Dave

02-04-2016, 09:32 AM   #5
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QuoteOriginally posted by davesofnj Quote
biz-engineer: I've just seen your reply. Sorry to hear you also have a similar problem. I'll see what happens with my DA-300. Wow! Looks like we do have the same problem. With the TC & DA-300, the K-3 won't focus with 27 points selected but worked like a charm with single point.
I know this problem, so I don't use 27 AF tracking when TC is mounted, I use 9 points and it works fine. To me, it's not that I had a faulty camera / lens, I think all K-3/K-3II have this same limitation (I have another problem that is AF does not always lock with center point with DA300... but I'm working on it). That said, there are a number of guys who are having their 7D+Tamy 150-600 AF servo that does not work...
02-04-2016, 10:37 AM   #6
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QuoteOriginally posted by Adam Quote
I also would try using all 27 AF points. Since the 150-450mm is in the F6.7 to F8 range with the TC, you're pushing the limits of the AF system and might not get the best results with a single AF point unless you're in bright daylight.
I believe your conclusion is the answer. The K-3 may be sensitive to EV(100) -3*, but the prisms used in the PDAF system will begin to "black out"** at about f/8 with the effect being worsened with other than bright conditions. The AF sensels are, quite literally, in the dark. In addition, the lower limit of -3 EV(100) is fairly easily attained in mildly dim light if f/8 is your maximum aperture. Experience has taught me that even above -3 EV(100) the AF performance begins to suffer if the target is of low contrast.


Steve

* It has never been clear to me what EV means in this context. The assumption I have made is that EV is used as a poor substitute for lux (illuminance). By the most generous assumptions, the K-3 lower limit would be taken to mean a meter reading of 30s at f/2.0 (ISO 100) or its equivalent at the same ISO.

** The black out phenomenon is equivalent to the black out seen with split-image and microprism focus aids on an SLR focus screen. Most will begin to fail somewhere between f/5.6 and f/8 with most being unusable by f/11.

Last edited by stevebrot; 02-04-2016 at 10:45 AM.
02-04-2016, 10:54 AM   #7
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What I don't like is that it goes to the short end and then gives up. It means that shooting at a moving object in the sky is a tough proposition. Perhaps I should try using a preset that forces it to infinity.

Dave
02-04-2016, 11:16 AM   #8
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What I do not understand is when shooting birds is why on earth do your leave the AF on its own to pick what to focus on. Normally birds are far enough away that they are in the middle of your viewfinder, and the remaining focus points are beyond the bird in the image. To me the camera simply sees a featureless background and just will give up because there is absolutely nothing to focus on.

Why the cams gives up, I don't know, but I suspect somehow it decides it wants an off centre focus spot. After all you asked to look at all of the sensors, so I think it assumes to ignore the centre one. It is trying to interpret focus of a composition that contains, well, nothing at all off centre

02-04-2016, 01:39 PM   #9
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Nothing to do with the amount of light. When using 27 AF point, the AF move to the shortest focus distance, even outdoor in fully sun weather, when using 9 points of center point only, it works, even with less light: the AF servo moves in the correct direction. When using 27 AF point, the AF move closer and does not perform a full range attempt as it does when it misses focus in a normal case.
02-04-2016, 01:49 PM   #10
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This problem all started when I was using single point.

1. It's not related to f/8 because it also happens with the f/5.6 300mm DA + 1.4x combination.

2. That it works first time after turning on the camera and then doesn't work, suggests a firmware problem rather that a basic failure.

3. This is a problem that has happened over the past couple of weeks. It did not happen during the first 60,000+ photos I took with this K-3, many of which were with either the DA 300mm or the 150-450mm both with and without the 1.4x.

It could be an aging issue. Or it could be some dirt has gotten into a vital area interfering with the AF (but see #2 above).

Time to take searching for repair options seriously.

Dave
02-04-2016, 02:33 PM   #11
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QuoteOriginally posted by biz-engineer Quote
Nothing to do with the amount of light. When using 27 AF point, the AF move to the shortest focus distance, even outdoor in fully sun weather, when using 9 points of center point only, it works, even with less light: the AF servo moves in the correct direction. When using 27 AF point, the AF move closer and does not perform a full range attempt as it does when it misses focus in a normal case.
QuoteOriginally posted by davesofnj Quote
This problem all started when I was using single point.

1. It's not related to f/8 because it also happens with the f/5.6 300mm DA + 1.4x combination.

2. That it works first time after turning on the camera and then doesn't work, suggests a firmware problem rather that a basic failure.

3. This is a problem that has happened over the past couple of weeks. It did not happen during the first 60,000+ photos I took with this K-3, many of which were with either the DA 300mm or the 150-450mm both with and without the 1.4x.

It could be an aging issue. Or it could be some dirt has gotten into a vital area interfering with the AF (but see #2 above).

Time to take searching for repair options seriously.

Dave
Sounds like 2 diffent problems, since one camera works in single and 9 point, the other not at all. Biz-engineer sounds like a hair or something on one AF sensor that is making the camera try to latch onto it

The other is either a general failure or maybe for both cameras just a lot of dust dirt, or fogging in the prism housing. Maybe look at the focusing screen, also, I forget on Pentax, are the AF sensors off a different mirror.
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