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01-04-2013, 02:54 PM   #16
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QuoteOriginally posted by westmill Quote
Tell me something I dont know lol
I just wonder about the SR problems. Can you explain?

01-04-2013, 03:04 PM   #17
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QuoteOriginally posted by VisualDarkness Quote
I just wonder about the SR problems. Can you explain?
Im sure I already have on here, but, I was getting loads of ooomph pics just like the OPs. It turned out to be the SR. Not a problem once I knew.
it just needs time to settle so it does not like shooting in quick succession. Thats why i was convinced it was SR. Until he posted the one with the sharp rail. I have not had any sharp areas if it was caused by the SR.
01-04-2013, 03:33 PM - 1 Like   #18
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I'm not so sure it is the same thing but I did have a similar problem with my K-r, that is inconsistent focusing even when set on a tripod in good lighting. It seems it was dirt on the focus sensors. One thing I had noticed (before fixing the problem) was that most of the focus points worked ok, only the centre one and one of the corner ones being inconsistent. I eventually sorted it out with compressed air, lots of it, perhaps even too much but it did fix the problem and it works just fine to this day.

Have you tried any of the other focus points - that might reveal whether the problem is in the sensor or not. If any of the other focus points works reliably then you can be sure that the problem is in the sensor and most likely just due to dirt.

I wouldn't recommend blasting compressed air randomly as I did but maybe a more gentle form of cleaning might solve your problem.
01-06-2013, 11:37 AM   #19
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QuoteOriginally posted by lister6520 Quote
Have you tried any of the other focus points - that might reveal whether the problem is in the sensor or not. If any of the other focus points works reliably then you can be sure that the problem is in the sensor and most likely just due to dirt.

I wouldn't recommend blasting compressed air randomly as I did but maybe a more gentle form of cleaning might solve your problem.
I will have to look into this, as I have not visually inspected the auto focus sensor. However, as I mentioned along the course of this thread, the errors only appear to occur when using wide angle focal lengths, i.e. around 17mm. I can't imagine a dirty sensor would some how be abated by an image projected by longer focal lengths. Still, it's worth checking out.

And while I'm on the subject of how focal length factors into this mess, I have not determined at what focal length things "clear up". Tests at 24mm, 35mm, and 50mm on my Tamron are all error free and reliable, but I don't know how far below 24mm I can go with any certainty without the same trouble as at 17mm.

01-06-2013, 05:13 PM   #20
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Doesn't look at all like motion blur to me. Looks like the lens never changed focus after focusing on your hand. With that sign nice and out of focus and Pentax's super-sized center focus point, maybe it couldn't find an edge to lock on in the image.

Of course then the question becomes why the camera would go ahead and take the shot with nothing to lock focus on.
01-06-2013, 10:41 PM   #21
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QuoteOriginally posted by bkpix Quote
Looks like the lens never changed focus after focusing on your hand.
I can say, with all certainty, the lens was definitely focusing nearly at the distance it should have. Throughout the testing procedure I took enough pictures in the sequence to both visually confirm the lens distance scale was at or near the "infinity" mark and watch the image become focused in the view finder (or obviously in some cases, almost focused). The sign was a good thirty-plus feet away, certainly falling at or near the "infinity" distance according to the test lenses.

For several exposures I actually watched the lens distance scale land on different focus points, even though I was photographing the same subject at a constant distance. The differences were subtle, but nevertheless, the result should be bang on every time considering my test subject is not moving, is naturally and brightly lit, and has its own inherent features with strong contrast. No properly function DSLR should struggle like this.
01-07-2013, 02:52 AM   #22
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Focusing at 16-18mm on distant (more than ~15m away) objects has always been inconsistent with my K-5, regardless of the lens used. My guess is that the SAFOX AF sensors just don't have enough resolution for the fine details of distant objects with wide angle lenses, maybe aberration of the lens and AF microlens optics are also partly at fault in these cases. I also noticed that when it's a miss in these cases then it's an absolute miss, i.e. nothing is in focus (at least you can't find any spot on the picture being in good focus). With parfocal zooms I just zoom to mid or tele FL, focus and lock focus, then zoom back to wide end and take picture - this works 99%.
01-07-2013, 09:19 AM   #23
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QuoteOriginally posted by simico Quote
Focusing at 16-18mm on distant (more than ~15m away) objects has always been inconsistent with my K-5, regardless of the lens used. My guess is that the SAFOX AF sensors just don't have enough resolution for the fine details of distant objects with wide angle lenses, maybe aberration of the lens and AF microlens optics are also partly at fault in these cases. I also noticed that when it's a miss in these cases then it's an absolute miss, i.e. nothing is in focus (at least you can't find any spot on the picture being in good focus).
While it's heartening to know at least one other person is experiencing something similar with the same camera model, I should point out this only became an issue once the camera came back from a different repair/adjustment process; it was sent in with two telephoto zooms to have those lenses calibrated to the body. I'd like to suggest your K5 is having the same problem as mine due to a fault with a component rather than a design inadequacy.

I can't imagine Pentax would design a DSLR body with a new AF mechanism that can't handle their existing stable of wide angle lenses, whether it be standard zooms like the 16-45mm, 16-50mm, 18-55mm kit lens, or even an ultra wide like the 12-24mm.

01-08-2013, 03:19 PM   #24
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For anyone interested/still reading, I spoke with a nice gentleman from CRIS named Steve. In his own words, he's one of the "older technicians" at the facility and the duties of calling back customers fall to him.

According to Steve, he has never heard of such a problem as what I'm describing, but he agrees this is not an issue of interference from the shake reduction mechanism. He also considered a dirty AF sensor, though he couldn't comment one way or the other on how that would somehow ignore longer focal lengths. He did say it would be extremely difficult to visually inspect the AF sensor since it faces away from the opening of the lens mount; I was already expecting that, as I have seen exploded diagrams and DSLR cross-sections from those poor bodies that have been cut in half.

Steve mentioned pressing on the rear elements of my Tamron with a lens cloth to see if they were loose. I tried this with no appreciable affect. I wasn't counting on this being a solution anyway since I have already established that the camera is exhibiting the symptoms with more than one lens.

The topic of the 18-55mm kit lens' resolving power also came up, and as expected, Steve talked about how that lens pales in comparison to higher end equipment. Never mind that the Pentax kit lenses are generally considered to be better (sharpness-wise, anyway) than the rest. What Steve was forgetting is that the issue is FOCUS consistency, not line pairs and resolving power. I feel like I need to submit a flow chart to keep the subject on target as it's the only thing I have not yet provided.

It looks like my only recourse is to send the body in (again) with the lenses. I'm not happy about this because 1) I'm getting nickel and dimed to death with shipping costs, not to mention that means I'm without my main camera (again) and 2) My fear is that CRIS will treat the symptom with a fix that will throw everything else out of place. As Steve explained it, a computer diagnostic system can mate the body to the lenses according to their shift. This would be fine if this were a simple matter of a consistent shift as in the case of a front/back focusing situation. However, I've already established the error is inconsistent. I expressed my misgivings about the situation, likening it to taking a car to a mechanic and the mechanic can't "hear the noise", if you take my meaning.
01-09-2013, 12:08 PM   #25
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So your SDM lenses are OK and your 2 screw drive lenses aren't? If that's so then the obvious conclusion seems to be there's something wrong with the screw drive. A lot of backlash perhaps which would definitely cause inconsistent AF .
01-09-2013, 05:30 PM   #26
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QuoteOriginally posted by SteveB Quote
So your SDM lenses are OK and your 2 screw drive lenses aren't? If that's so then the obvious conclusion seems to be there's something wrong with the screw drive. A lot of backlash perhaps which would definitely cause inconsistent AF .
The two lenses I've been using to test for the error are the traditional screw drive AF variety. However, the issue is specific to wide angle lenses, or at least wide angle zooms set to their widest focal length. My 50mm and 90mm macros, my DA L 35mm 2.4, and my 55-300mm all work splendidly, and these lenses are all non SDM.

The screw drive mechanism was brought up in the conversation with Steve from CRIS, but neither one of us volunteered an idea why screw drive in combination with wide angle focal length make for inconsistent AF distance judgement on the part of the camera.
01-16-2013, 06:01 AM   #27
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It appears like the camera is failing to find a focus lock and just stopping the lens at minimum focus distance. I think perhaps they should offer you a replacement.
01-16-2013, 11:32 AM   #28
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It does happen with my K5 too, wide angle is hard for some reason. But mostly this is a problem in low light situations with my K5. I do however have a habit since the K10d days to press AF several times (when there is time) and slightly shift the camera around to make sure that the AF sort of settles at one setting. With a wide lens the AF surprisingly often hunts back and forth when doing so.

Sometimes (and perhaps not with all lenses) it's better to zoom in, focus, zoom out and shoot.
01-16-2013, 08:06 PM   #29
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QuoteOriginally posted by Gimbal Quote
It does happen with my K5 too, wide angle is hard for some reason. But mostly this is a problem in low light situations with my K5. I do however have a habit since the K10d days to press AF several times (when there is time) and slightly shift the camera around to make sure that the AF sort of settles at one setting. With a wide lens the AF surprisingly often hunts back and forth when doing so.
I have noticed my 18-55mm kit lens does a little dance when auto focusing; it seems to stop a little before the correct focus point and then jump to the correct point. In the case of my preferred Tamron 17-50mm, the lens always stops in exactly one place. No dancing. For both lenses, however, if the camera actually determines the correct focus point is hit or miss.

I'll also mention (and repeat) the fact that this AF inconsistency on the part of the K-5 was not a problem until the camera came back from CRIS for a general check and lens calibration.

There was a mention earlier in the thread about lens resolution and aberrations as a factor in my situation. I hadn't fully formed an opinion about the science of that possibility until recently. If one is to trust the reviews by guys like Photozone.de and Lenstip the Tamron lens from my test images actually has the highest center sharpness at its widest focal length which is precisely where I'm encountering the problem. In other words, if resolution is the key to all this, the lens should actually perform worse at longer focal lengths, not to mention worse resolving lenses would also be giving me problems. Of course, I've stated I know little about the alchemy that goes on with phase detection AF mechanisms, so I'm sure there's plenty I haven't considered here. Nevertheless, if I only had numbers to go by I'd be inclined to rule out the resolution of the glass.
01-17-2013, 10:35 AM   #30
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When I turned off the autofocus on my shutter release button and switched to only using the autofocus button on the back of the camera body it improved my keeps substantially. I learned this trick from a Nikon user who has been shooting this way for years. takes a couple of outings to get into the hang of it, but now it comes naturally and I have made this change to both my K10d and my K5 bodies.
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