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12-02-2008, 07:42 AM   #1
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Focusing screen and effects??

I put a little scratch on my focusing screen while trying to change it out. I also got a couple specs of dust behind there also. ( I should have waited until I was fully awake because I'm usuallly pretty good at this sort of thing. )

Anyway, I have been using it with what seem to be no problems the last week or so but I was wondering if the screen has any effect on auto or manual focus. The screen is only viewing the object and does not effect what the sensor picks up right ?? I know the light from the screen does effect the exposure but it shouldn't effect the focus should it?


Thanks

12-02-2008, 09:00 AM   #2
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Well, it is called a focusing screen for a reason :-). It isn't involved in AF, but it is quite literally what you are looking at when focusing. The lens projects an image onto the screen, and that's what you see through the viewfinder. So if there's a scratch on the screen, you'll probably see some some remnant of it through the viewfinder. Probably in the form of a spot that never seems to get completely sharp, which could make it difficult to focus while looking at that particular spot. But for the most part, sure, you'll still be able to focus - just don't rely too much on looking at that spot.
12-02-2008, 11:15 PM   #3
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Your pictures will be fine. My focus screen is scratched and dusty too.
12-03-2008, 12:16 AM   #4
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Thread-jack while we're on topic: can you put a focus screen in the K200D?

12-03-2008, 05:16 AM   #5
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I would venture to say yes. I believe all focus screen are interchangeable.

Thanks Marc and innershell.
I have another screen on its way but this time I am going to make sure I"m awake before I swap it out.
12-03-2008, 06:26 AM   #6
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QuoteOriginally posted by OrenMc Quote
I put a little scratch on my focusing screen while trying to change it out. I also got a couple specs of dust behind there also. ( I should have waited until I was fully awake because I'm usuallly pretty good at this sort of thing. )

Anyway, I have been using it with what seem to be no problems the last week or so but I was wondering if the screen has any effect on auto or manual focus. The screen is only viewing the object and does not effect what the sensor picks up right ?? I know the light from the screen does effect the exposure but it shouldn't effect the focus should it?


Thanks
It will have no effect, other than the annoyance.
I dropped my Katz-Eye while installing it and put a ding in it. Annoying as heck, especially given how expensive they are, but other than a spot just below left center, it's all good.
I used to draw crop lines onto my Nikon screens with a sharp pencil to ensure that I was always within the 8x10 crop.
12-03-2008, 07:24 AM   #7
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QuoteOriginally posted by OrenMc Quote
I put a little scratch on my focusing screen while trying to change it out. I also got a couple specs of dust behind there also. ( I should have waited until I was fully awake because I'm usuallly pretty good at this sort of thing. )

Anyway, I have been using it with what seem to be no problems the last week or so but I was wondering if the screen has any effect on auto or manual focus. The screen is only viewing the object and does not effect what the sensor picks up right ?? I know the light from the screen does effect the exposure but it shouldn't effect the focus should it?


Thanks
AF module is on the bottom floor of the mirror box. Light going to the instant return mirror (semi-silvered) goes through the mirror and is reflected down by a second mirror that is behind it. That beam then goes through a bunch of mirrs/lenses/prisms to do the AF.....
No a scratch on the screen will not effect AF.
7 is the AF module
1 is the exposure module
Photo courtesy of Mr. Dimitrov
Pentax Auto Focus Systems
12-03-2008, 01:16 PM   #8
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As others have said already, it will have no detrimental effects apart from annoying the hell out of you when you look throught the viewfinder.

Get over that and enjoy your photography.

12-03-2008, 08:56 PM   #9
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QuoteOriginally posted by kerrowdown Quote
Get over that and enjoy your photography.
I won't skip a beat. I received my new K20D today!
I have a replacement screen coming and when I get that cleaned up the 10d goes up for sale.

Thanks for the clarification. Since it is going on the block I want to make sure everything is kosher. I will take it in this weekend and have the techs look at it also. I have been using it with no problems except being a little annoyed just know the scratch is there. But its up in the far right corner so out of most of the view.

jeffkrol, great diagram. Thanks

wheatfield, quite resourseful using the pencil.

Thanks again.

Last edited by OrenMc; 12-03-2008 at 09:02 PM.
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