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05-31-2015, 01:35 AM   #1
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Screen not matching Sensor focus plane

I am using a KatzEye Focusing Screen with my K-3.
Until recently, all was good - when the screen's split prism showed a perfect focus, the image was in focus as well.

But today I noticed that all the lenses are font focusing: Both when using Phase-detection-AF and when using the screen for manual focusing.

I wonder what could have happened there. I did not drop this camera. I also kept it in moderate (room) temperature all this time.

Since both the PD-AF and the screen are off by the same amount, I also conclude that it's not the screen that has moved. It's probably the mirror position that has shifted, as only that would affect both, am I right?

Now I wonder what to do. Send in the camera? Would that be a clear warranty case?

Alternatively, does someone know if opening the camera at the bottom gives relatively easy access to the adjustments for the mirror position? Or is that something one cannot do without lab equipment?

05-31-2015, 03:22 AM   #2
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QuoteOriginally posted by tempelorg Quote
Would that be a clear warranty case?
I doubt it with an after market view screen installed. If you are going to send it in I would recommend putting back in the viewscreen that came with it first.
05-31-2015, 04:39 AM   #3
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I would not mess with the mirror. No way. What you can do is to check if the K mount on the camera does have some movement. Even it is hard to believe that the screws that keep the mount in place has begin to unscrew by themself overnight.

Other thing that you can do is to lift the mirror, like what you do when you want to clean the sensor, and to look at the back side of it. The main mirror has another smaller one attached to it backside in the center, and this is the one that send the light to the focusing sensor. Maybe some dust prevent the smaller mirror to sit in the right position. Try an air blower, to clean the place, both when the mirror is up and second, when the mirror is in his normal position, but without touching the face of the mirror.

If it doesn't work, go to the ''doctor''.
05-31-2015, 07:30 AM   #4
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I'd put the original stock screen back (and re-test it while you're at it, just in case), and then (if it's still off) send the cam out for a clear warranty fix.

I would ~not~ fiddle with the mirror.

I agree, if both MF and AF are off, that the mirror is more suspect than the screen.

Good luck.

05-31-2015, 10:32 AM   #5
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If both the screen and the phase-detection AF are out of focus, then it can't be the screen. So, Pentax would have no right to claim that the 3rd party screen could cause this. Plus, putting a screen in is not an unsanctioned hack either. But yes, I would not send in the camera with the KatzEye screen anyway, for the same reason I wouldn't include my SD Card or other non-essential parts.

JimmyDranox makes an interesting point. I do not agree with that, though, because if the secondary mirror would be out of line, then that would only affect the AF sensor but not the screen.

I just don't want to send in the camera right now if there's possibly an easy fix as I need it in 3 weeks and I have my doubts I'd get it back by then.

However, I have found a discussion thread, at dpreview, I believe, where someone quite familiar with Pentax repair manuals, claimed that it's rather normal that the mirror system ages and shifts over the years, and says that that's the reason why Pentax offers a tune-up and suggests to have the body serviced regularly (in 1-2 year intervals). He also explained that the body has active compensations depending on the temperature for that, too. The thread was about the K-10D, but I wonder if the same still applies, if it's true what he wrote.

I cannot find the thread again but I found this with a nice picture of showing the whole mirror + AF system in case someone here hasn't seen it yet:

Re: Badly aligned focus on K10D - tested!: Pentax SLR Talk Forum: Digital Photography Review

But at least I found the post I had in mind when I asked about making adjustments myself. See here:

RiceHigh's Pentax Blog: Hardware Adjust a Pentax DSLR for the AF

Still, I guess I'd need the K-3 service manual for that, and that's rather difficult to find.
05-31-2015, 01:21 PM   #6
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QuoteOriginally posted by tempelorg Quote
If both the screen and the phase-detection AF are out of focus, then it can't be the screen. So, Pentax would have no right to claim that the 3rd party screen could cause this. Plus, putting a screen in is not an unsanctioned hack either. But yes, I would not send in the camera with the KatzEye screen anyway, for the same reason I wouldn't include my SD Card or other non-essential parts.
Well, while I agree with not sending any non-essential parts along with the body, I would most ~not~ want to send the KatzEye along because, despite the fact that it should not affect the mirror alignment, I wouldn't want some lame repair tech trying to blame the repair on the simple installation of a 3rd-party focus screen -- it just isn't worth the hassle of such an argument.
05-31-2015, 01:26 PM   #7
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Fred, whatever you say. But that's besides the point. I like to keep the discussion on the original topic and not get sidetracked on policies, so please let's just drop this business about whether the card needs to be removed for service. It's an advice I've received but please let's get back on topic.
06-01-2015, 02:39 PM   #8
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QuoteOriginally posted by tempelorg Quote
If both the screen and the phase-detection AF are out of focus, then it can't be the screen.
There might be issues with the calibration of both, though the chances of both happening out of the blue at the same time are remote. As noted above, the two systems are separate and distinct. A misaligned mirror might affect both, but for the PDAF the problem would likely be complete failure. In such case, the viewfinder image would be sharper at top or bottom and very strange looking.

One possibility is that the camera has been dropped resulting in the sensor being displaced. That would affect both the PDAF and focus screen accuracy.


Steve

06-01-2015, 02:45 PM   #9
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One day on my K-5 the on-board flash suddenly stopped working (wasn't dropped, just one shot to another). At the same time, suddenly it was as if the sensor had moved -- my carefully calibrated focus screen was no longer accurate and the AF on the lens that I had been using a moment earlier was also way off. Had to send it in anyway to get the flash replaced (work order said it was shorted out or something) and so told them the focus was off (had to put my stock screen back in) and they re-calibrated it, but it was strange. Could it actually be an electronic cause?
06-20-2015, 05:05 AM   #10
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K-3 does image stabilisation by main CMOS sensor shift or swing. Your description of problem match, if something wrong or different in this subsystem.
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