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04-29-2017, 03:18 PM   #1
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Pentax K10D with split focusing screen - various questions

Greetings!

I have a K10D with a microprism/horizontal split focusing screen installed. It's not as finely crafted as a Pentax original... a little-bit rougher, has a little bit more gap between the upper-and-lower parts than the one in my MX. However it's quite usable.I got the screen as a gift from a friend of mine, so I can't be sure of the origins. It came in a little red plastic box. I found great joy in its' use, since I have a few legacy glass... and before I had my Pentax MX, it was my best choice for a manual focusing camera. It really makes focusing a breeze!
However over time I found that it brought up various issues.
First and foremost: when using it with an autofocus lens to test accuracy, it seems that its' accuracy varies when I adjust the dioptier on the camera. I wear glasses (-1,75 on my dominant right eye, -1,25 on the left). If I set the diopter all the way to the right, then the inner readings are perfectly razor sharp... but the alignment of the prism shifts a little, so I have to take it two steps back. What could be the reason? This of course also affects somehow, how accurately different lenses focus manually. Now how to determine how to calibrate the diopter correctly?

The second is if it could be causing back-focus. I just got myself a DA 35mm f2.4 lens third hand for cheap. The lens itself is great, using it with MF is perfectly accurate... more accurate than AF. Could the split focusing screen be affecting its' focusing accuracy? The lens is perfectly sharp, but it doesn't focus perfectly when wide open - it back focuses.

The third is if could affect metering? Only on one lens though: my Tokina SZ-X SD II 28-70mm f/3.5-4.5 seriously overexposes... about one stop with this lens. More so closer to the longer end. Or could this be because it's only a KA mount lens with a variable aperture?

These are small technical questions which have been bothering me for a while. I've been using my K10D with the split screen for about half a year now. I've yet to take it for a test drive with the original screen. But some insight on such details would be welcome!

04-29-2017, 03:56 PM   #2
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The viewfinder screen should not affect Autofocus.

The viewfinder screen with things in the middle can affect exposure. When looking through the viewfinder with the offending lens, pull the power switch past the ON setting to the stop down setting. You will probably see one or the other side of the prism turns black. This will cause overexposure.

I don't see how the viewfinder screen can affect the lens' front or back focus. The path from the lens to the AF module is not the same as the screen, which is above the mirror.
04-29-2017, 04:50 PM   #3
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Spot metering will be affected by the microprism/horizontal split portion of the focusing screen. Avoid it. The other forms of metering should not be affected. Autofocus will not be affected.
04-29-2017, 07:27 PM   #4
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I have had metering troubles with center weighted as well as spot with my K10D. I haven't used a special screen on the K-3.

04-30-2017, 12:39 PM   #5
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I have been thinking of getting a different focussing screen for my K10D. It would make the use of my manual focus lenses easier. The issues with spot metering are new to me. Then again, I don't use spot metering very much.

From what I have seen on the web, it seems easy enough to swap the factory screen back in when needed. In my film days I used a selection of focusing screens with my LX. The drill looks familiar.
04-30-2017, 12:46 PM   #6
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QuoteOriginally posted by Canada_Rockies Quote
I have had metering troubles with center weighted as well as spot with my K10D.
Interesting, and not what I would expect. Mind you, I have only used multi-segmented metering up to now; it suits the way I shoot. I'm using KatzEye screens, and their web site indicated problems only with spot metering.

QuoteOriginally posted by Wasp Quote
The drill looks familiar.
The drill is the same.
04-30-2017, 02:53 PM   #7
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QuoteOriginally posted by cpk Quote
Interesting, and not what I would expect. Mind you, I have only used multi-segmented metering up to now; it suits the way I shoot. I'm using KatzEye screens, and their web site indicated problems only with spot metering.
With M or K lenses the only option is Centre weighted, and the problem can occur with them.
QuoteQuote:
The drill is the same.
Identical. Just as fiddly, and just as easy when you get the hang of it.
04-30-2017, 03:16 PM   #8
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QuoteOriginally posted by Canada_Rockies Quote
With M or K lenses the only option is Centre weighted, and the problem can occur with them.
Thanks for the warning. I use my M lenses only occasionally, like almost never; so I haven't noticed the problem.

QuoteOriginally posted by Canada_Rockies Quote
Identical. Just as fiddly, and just as easy when you get the hang of it.
I hate changing screens. It stresses me out, trying not to slip and damage something and trying to keep everything clean. Thankfully I do it only once per camera (except my K-7 where I moved the KatzEye screen to my K-5 II when I converted the former to IR). But now I have to play with the shims on the K-5 II (more stress).

04-30-2017, 03:50 PM   #9
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QuoteOriginally posted by cpk Quote
Thanks for the warning. I use my M lenses only occasionally, like almost never; so I haven't noticed the problem.
I use my M 400 quite a lot, and until I got my used FA 100 macro, an M 100/4 macro. As my minuscule budget permits, I'm switching to at least A lenses.
05-01-2017, 09:41 PM   #10
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I installed a Katzeye (sadly no longer in business) split-prism screen to my K10. Did not present any exposure issues with multi-segment exposures when used with a modern lens. Spot metering was unreliable though. The Katzeye was the best quality of split-prism, and from what I remembered at the time, other brands could present issues.

I remember when first getting my K10 with the stock screen that the metering was very off with legacy K and m lenses, mostly causing a progressive overexposure as the lens was stopped down. After installing the katzeye, the problem was still there, but not as bad.
05-03-2017, 12:08 PM   #11
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QuoteOriginally posted by pschlute Quote
I installed a Katzeye (sadly no longer in business) split-prism screen to my K10. Did not present any exposure issues with multi-segment exposures when used with a modern lens. Spot metering was unreliable though.
What Peter said ^ ^ ^

I can't speak for brands other than KatzEye, but my K10D metered reliably with their screen* when used with A-contact lenses for six of the seven years that I owned that camera. I did lose spot metering, but did not miss it; spot metering being very much a special purpose tool.


Steve

* I actually did comparison readings against the stock screen, but have since lost the data
05-03-2017, 08:50 PM   #12
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QuoteOriginally posted by stevebrot Quote
What Peter said ^ ^ ^

I can't speak for brands other than KatzEye, but my K10D metered reliably with their screen* when used with A-contact lenses for six of the seven years that I owned that camera. I did lose spot metering, but did not miss it; spot metering being very much a special purpose tool.


Steve

* I actually did comparison readings against the stock screen, but have since lost the data
I had problems metering only with M and K lenses. Never used my Taks on it. I think the center weighted metering is affected, but with a lesser impact than spot metering. My solution to the whole mess, transferred in a couple of seconds to my K-3, is the O-ME53 magnifier. And always carefully setting the diopter in the eyepiece every time out. It gives just enough magnification that I can focus on the screen without aids. Of course, it might be easier with practice. I was manual focus only from 1961 through 1981.
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