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Old Apr 14, 2010, 8:12 AM   #1
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Default Line pattern in view finder

I noticed a fine circular line pattern in the viewfinder of my K7 while shooting up at the sky the other day. Is this in the prism? At first I thought it was a finger print, but it is actually a circular pattern barely visible.
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Old Apr 14, 2010, 11:28 AM   #2
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Hi Tony,

I believe this is a normal Fresnel pattern on the focusing screen (which is, BTW user changeable in Pentax DSLRs). You could take it out and get a closer look, but for me, it's one of those "if it ain't broke, don't mess with it" things, since they are made of a pretty soft plastic that's very easy to scratch, and prone to damage from fingerprints.

The prism is a completely clear hunk of glass.

Scott
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Old Apr 14, 2010, 3:02 PM   #3
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What Scott said. I remember noticing that the pattern on the focusing screen was a little more pronounced on the K-7 than the K20, but that it was also a bit easier to see the focus through it. After that I forgot about it until reading your post.
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Old Apr 14, 2010, 3:39 PM   #4
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So it is normal then, correct?
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Old Apr 14, 2010, 4:17 PM   #5
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Do you guys think it is worth changing the focus screen to a split prism ? Is it more accurate for manual focusing ?

Sorry Tony - don't mean to hijack your thread
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Old Apr 14, 2010, 5:22 PM   #6
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Quote:
Originally Posted by mtngal View Post
What Scott said. I remember noticing that the pattern on the focusing screen was a little more pronounced on the K-7 than the K20, but that it was also a bit easier to see the focus through it. After that I forgot about it until reading your post.
Hi Harriet,

It's more pronounced with the K-7 because of the slightly darker focusing screen, which was used in the K-7 to make critical focus easier to see.

Scott
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Old Apr 14, 2010, 5:52 PM   #7
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Quote:
Originally Posted by tony3dd View Post
So it is normal then, correct?
Hi Tony,

It's totally normal


Quote:
Originally Posted by Frogfish View Post
Do you guys think it is worth changing the focus screen to a split prism ? Is it more accurate for manual focusing ?
Hi FF,

Split screens are totally a matter of personal taste. The absolute accuracy is dependent on correct shimming of the focusing screen (as is the OEM screen, but the assumption is that this is done at the factory when the camera is built. Aftermarket split screens can be a number of thousanths off, yet still be up to factory spec, so the luck of the draw enters into the discussion). With accurate testing and a set of focusing screen shims, you can get very precise focusing accuracy, but the focusing screens are pretty fragile, and I don't have the patience and nerves to make sure I do the job right -- but it's very possible I'm being way too fussy in this. . .


Another minus point of split screens is that they are known to effect exposure significantly when using spot metering -- but the differences are usually linear, so you probably can get away with determining the Ev difference and applying a set amount of Ev compensation to offset the error.

I own two split screens. One Katzeye standard that I still have in my DS, and a jnfinance from ebay that is a 45 degree split screen that I decided not to use. My other 4 Pentax DSLR bodies have OEM screens. Personally, I find the usual split screen with microprism collar takes up too much space in the APS C viewfinder (everybody uses existing 35mm focusing screens or screens designed for 35mm, and the area fills too much of the VF, IMO). Also, 1/2 of the split screen will black out with slower max aperture lenses, and in lower light, and I use TCs a lot, which give slower max apertures, so the blackout becomes a common problem for me. You usually can avoid some of the blackout by moving your eye very slightly, but for birding, this is just another thing I don't need that slows down my ability to get the shot. If I were to get another accessory focusing screen, I'd probably want a small central microprism dot only, maybe with "rule of thirds" or 8x10 crop lines only, but I'm probably the only one who'd want one of these, so I'm not holding my breath that someone will make one. . .

Bottom line -- a lot of people like them -- I've found them not that desirable for my purposes -- YMMV

Scott
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Old Apr 14, 2010, 11:46 PM   #8
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My two cents about split screens - I used one in a film camera for many years and at first had a hard time adjusting to the screen on the DS. However, the half-black phenomenon always drove me nuts, though I didn't run into it very often and didn't know what caused it. I thought about getting one for the DS, but didn't get around to it before getting a macro lens. Practicing with that sharp macro lens made a big difference - by the time I decided I could afford one I realized that I had no real problem seeing the focus with the OEM screen. I still haven't bothered getting one.
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Old Apr 15, 2010, 1:05 AM   #9
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Thanks everyone.
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