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02-16-2011, 08:47 PM   #1
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Focusing screen issue. Split-screen out of whack?

This has me puzzled. I have a split-field focusing screen on my K10D. I installed it about two years ago and it was lining up nicely, coinciding with the beeps that confirm correct focus. Over time I suspected it wasn't quite lining up as well as before, but I thought that must just be my imagination.

But yesterday I picked up the camera for the first time in weeks and took some shot, and noticed that the split was severely out of alignment at the point when the camera confirmed good focus. The resulting shots show that the subjects were indeed in focus, despite the split-screen alignment being out.

As I said, the screen was originally lining up nicely. It is possible for it to gradually go out of alignment? Can anything be done to correct it?

Thanks in advance.

02-16-2011, 09:38 PM   #2
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This is just a guess but could the shims have moved over time? I know that if you install a new screen, sometimes without shims they will not show the image in focus even though it is. If your current shims are moving that could cause the same problem.
02-16-2011, 10:40 PM   #3
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You can check the focus using a moire' target. That method is easy to do and very accurate. Even easier...Is the split image proper at infinity? (Think tall building at 1/4 mile distance.)


Steve
02-16-2011, 10:53 PM   #4
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QuoteOriginally posted by KxBlaze Quote
This is just a guess but could the shims have moved over time?.
So, not being familiar with shims, what are we talking about? I presume these are thin layers of something. If I were to inspect the screen, would I see them easily?

02-16-2011, 11:05 PM   #5
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I am only guessing. Since AF is accurate, the problem cannot be the mirror either. That leaves the focusing screen. It MIGHT be possible that the screen was thicker than the OEM one, and in time it pushed the whole prism assembly upward which is held by 3 or 4 tiny spring-loaded screws. Or the last time you install the screen, the metal clip was pushed too hard and caused misalignment (same result). If that was the case, the prism/screen assembly position must be re-adjusted by a handful of service centres for really accurate focus across the screen (not just the centre). B4 sending it out for service, you might reload the screen and see if it fixed the problem. Good luck.
02-17-2011, 11:07 AM   #6
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QuoteOriginally posted by marcdsgn Quote
So, not being familiar with shims, what are we talking about? I presume these are thin layers of something. If I were to inspect the screen, would I see them easily?
Shims are just pieces of material that are inserted on either side of the screen to make sure that the screen is centered to match the original. If you do not remember inserting shims when you installed your current screen then you do not have them and that obviously cannot be the source of your problem. Sorry, that's the only idea I had.
02-17-2011, 11:38 AM   #7
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I had a similar problem when I installed a split screen in my K200d. The red focus indicator was to the right of center when the subject was in focus. I had to move the focusing screen right or left ever so slightly to center to the red indicator. Just a thought; is your focus point set to center? If not it could be showing some other position on the screen.
02-18-2011, 06:52 PM   #8
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QuoteOriginally posted by jlamorie Quote
I had a similar problem when I installed a split screen in my K200d. The red focus indicator was to the right of center when the subject was in focus. I had to move the focusing screen right or left ever so slightly to center to the red indicator. Just a thought; is your focus point set to center? If not it could be showing some other position on the screen.
Just a simple point here but the red indicator is not a focus indicator, that is the green hexagon. The red indicator only indicates which focus point is active

02-18-2011, 07:08 PM   #9
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QuoteOriginally posted by Lowell Goudge Quote
Just a simple point here but the red indicator is not a focus indicator, that is the green hexagon. The red indicator only indicates which focus point is active
I think that was what I was saying and was included in my suggestion.
Regards
02-22-2011, 08:36 PM   #10
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UPDATE:

Well, the puzzlement continues after a weekend shoot at a national park. I used a couple of different lenses and switched between manual and auto focus, and can't seem to pinpoint a consistent issue. It appears that if I manual focus and line up the split-screen - (ignoring the focus sensor beep) - the focus is correct. But if I'm on auto-focus, the sensor is correct and the split screen is wrong.

I guess I have to factor in issues such as various levels of ambient light which could be interfering with correct readings and so on (??), but I'm having a h-ll of a time nutting this one out.
02-23-2011, 12:28 AM   #11
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That means the vf disagree with AF. The question is, which is accurate?
02-24-2011, 03:13 PM   #12
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QuoteOriginally posted by marcdsgn Quote
UPDATE:

Well, the puzzlement continues after a weekend shoot at a national park. I used a couple of different lenses and switched between manual and auto focus, and can't seem to pinpoint a consistent issue. It appears that if I manual focus and line up the split-screen - (ignoring the focus sensor beep) - the focus is correct. But if I'm on auto-focus, the sensor is correct and the split screen is wrong.

I guess I have to factor in issues such as various levels of ambient light which could be interfering with correct readings and so on (??), but I'm having a h-ll of a time nutting this one out.
So that means the problem is solved, isnt' it? When you use the manual lens, the focusing screen works well; when you use the AF lens, you don't need to see the split image. Good.
02-24-2011, 04:06 PM   #13
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QuoteOriginally posted by metalmania Quote
So that means the problem is solved, isnt' it? When you use the manual lens, the focusing screen works well; when you use the AF lens, you don't need to see the split image. Good.
No, as the O.P describes, it only proves that the [unexplained] problem exists.

I have a similar problem to the O.P, in that my split-prism when manually focused accurately, does not correspond with what the camera's A.F system will select as correct focus for an exact same subject, using any exact same lens.

One focus decision is obviously wrong. (Irrespective of which.)

Otoh; A standard Pentax focus screen, if fitted in the same camera, does not present that difference when used either MF or AF.
Go figure...

.R. -- ?
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