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01-05-2019, 11:41 AM   #1
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K3 + 50-135 focus difference - landscape vs portrait orientation

I think you can already guess the problem from the title.

My 50-135 hunts a little and doesn't lock focus sometimes in landscape orientation. There's this frantic jitter it does before locking focus (or simply stopping and not locking anything). It's always almost in focus.

In portrait orientation there is no issue at all. Focus is sharp and fast.

Anyone have any ideas? Lens seems to be "clean". Some microdust, but nothing noticeable. Af sensor and submirror doesn't seem to be dirty. *The submirror did suffer from the usual "delaminatin" issue, but the spots haven't returned in the middle, so that can't be the issue. Is it the lens? Can't be. Why would the lens play a role if it's in landscape or portrait orientation?! Has to be the K3. But what, why? LV has no issues.

Any suggestion helps! Thanks.

01-05-2019, 12:11 PM   #2
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The position of some of the AF sensors change between portrait and landscape, but I am not sure if that is related to the problem.
01-05-2019, 12:25 PM   #3
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it does turn 90'
I'm using center dot in both cases.
But it should be a crosstype sensor so the orientation shouldn't matter or what?

:/ I feel like the time gets closer and closer when I'll stop buying used equipment.
01-05-2019, 09:46 PM   #4
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SDM or screwdrive? If sdm I'm betting it is weakening. I've seen a few 50-135's with weird failure to lock focus improved dramatically with conversion.

My reason for the thinking is that SDM seems to give up easier than screw drive. The orientation could be adding a tiny amount of friction or otherwise altering the drive just enough to change results. Pure speculation based on other weird observed behaviours.

01-06-2019, 04:48 AM   #5
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okay, I'll keep that in mind. I don't have a pentax camera that can read/change the lens data atm.
01-06-2019, 07:50 AM   #6
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QuoteOriginally posted by labidas Quote
okay, I'll keep that in mind. I don't have a pentax camera that can read/change the lens data atm.
I offer conversion services but it isn't hard. See if anyone in your area has a body you could borrow.
01-20-2019, 05:52 AM   #7
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Thought I'd give an update :P
I "massaged" my SDM a bit and cleaned the mirror, submirror and AF sensor lens as best as I could.
Focus issues went away.
I feel so stupid, but that just shows one thing: Even a tiny piece of dust in the wrong place can cause focus issues. I never expected that.
I'm considering taking my camera into professional cleaning instead now. The lens seems to function fine.

*I mostly shoot with the center spot. When I used another spot, the focusing seemed much more accurate. That made realize there has to be something interfering with the center focusing point.
01-22-2019, 01:32 AM   #8
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QuoteOriginally posted by labidas Quote
...

:/ I feel like the time gets closer and closer when I'll stop buying used equipment.
you and me both, bud! (recent bad experience with a used lens purchased from a major retailer who refused to honor its warranty.)

03-24-2019, 07:49 AM   #9
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converted the lens, the issue still remains :/
Trying to focus on an A4 paper with small, but fat text. The K3 misses in landscape orientation by a long shot. Turn it to portrait orientation and voila, in focus.
Doing the same test on my wallpaper, the opposite happens. Portrait orientation misses, landscape is in focus.

Same test with a rented K20D - 0 issues.
Off to the repair shop with that K3. I hope they don't charge a kidney
03-24-2019, 12:58 PM   #10
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If it was consistent I would have suspected the cross point af sensor is broken and only works in one direction...
03-25-2019, 06:05 AM   #11
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As a sidenote, the AF seems to be more decisive and accurate now that it's screw-driven.
The repair has to wait though. I have a wedding coming up in 12 days. I'll rent a K1 + 15-30 + 24-70 and keep the K3 + 50-135 as a second camera for reach.
03-25-2019, 02:50 PM   #12
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Take a look at this thread: K3 center focus point - PentaxForums.com

It appears that the center (three vertically) sensors are not cross sensors, but a combination of sensor types. I don't understand this all that well, and at the very least, I would test with a focus chart instead of random text on a page before assuming it needs repair. Hopefully it doesn't need service.
03-26-2019, 05:55 AM   #13
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Essentially the horizontal part of the cross is f2.8 sensitive, and the vertical is slower. These are two separate sensors rather than a single cross type. So depending on the subject focus might be more reliable in one orientation than the other at low light with fast lenses.
03-26-2019, 09:42 AM   #14
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QuoteOriginally posted by labidas Quote
converted the lens, the issue still remains :/
Trying to focus on an A4 paper with small, but fat text. The K3 misses in landscape orientation by a long shot. Turn it to portrait orientation and voila, in focus.
Doing the same test on my wallpaper, the opposite happens. Portrait orientation misses, landscape is in focus.

Same test with a rented K20D - 0 issues.
Off to the repair shop with that K3. I hope they don't charge a kidney
Have you tried other lenses? I would imagine that would help determine the issue, too. If it's the camera, then the problem should occur on at least one other lens.
03-26-2019, 02:32 PM   #15
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Tried with another lens today.
I used a bright LED flashlight to light my wallpaper in a room with 3 lightbulbs working.
I tested with the center focus point(the 2.8 sensor) AND the one just right to the center (so not a f2.8 sensor).

Same issue and it's consistent.

https://flic.kr/p/RyMPov

https://flic.kr/p/2fftSpA

I was kinda relieved and devastated at the same time atleast my lenses seem to be working like they should. The K3 however... hmm.
Gotta sell that sucker quick and get a replacement, haha.
Funnily enough, I bought this camera from a photographer and she claimed she never had any issues.
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