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10-02-2014, 04:03 PM   #1
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Is my prism supposed to be clear?

New dslr owner with a new K-50. I hope this isn't a silly question (they do exist)

While looking through my viewfinder, I have noticed it isn't a perfectly clear image. It is something that looks almost like a fuzzy pattern. It is hard to describe. Maybe like it is frosted a tiny bit, but not that bad.

I removed my nifty kit lens and cleaned the front lens well, but have the same result. I removed the lens and noticed that looking through the viewfinder provides the same strange patterns. I gently brushed the mirror and the bottom of the prism (there was some dust there, but the view is still unclear.

is it a grind thing. Is it normal?
Do I need to replace my camera?

Thanks in advance to all that might help.

EDIT: Is this the focusing screen?

EDIT 2: I need to take the K-50 in for a cleaning. My examining and dust blowing have resulted in an incredibly messy view. It seems that the multitude of objects stuck there is worsening. It seems to small foreign objects may perhaps be above the focusing screen, as no amount of clean compressed air (not canned) is removing them.

Lesson learned. This will cost me, but once cleaned, I am simply not taking this kit lens off until I have to (or buy another lens).


Last edited by Schick; 10-02-2014 at 09:19 PM. Reason: New info
10-02-2014, 04:13 PM - 2 Likes   #2
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QuoteOriginally posted by Schick Quote
While looking through my viewfinder, I have noticed it isn't a perfectly clear image. It is something that looks almost like a fuzzy pattern. It is hard to describe. Maybe like it is frosted a tiny bit, but not that bad.
This question comes up periodically and the answer usually involves one or more of the following tidbits:
  • In order to show the projected image, the focusing screen requires a matte/textured surface to scatter the light. All reflex viewfinders (the "R" in SLR) as well as focus system for view cameras share this requirement. This textured surface can be as simple as ground glass or as complex as a microscopic array of tiny prisms.
  • Your focus screen includes a Fresnel lens as part of its construction. It is there to make the screen brighter and to provide magnification. The Fresnel lens is made of a series of concentric ridged arcs. To see the pattern set your aperture at about f/8, point the camera at the sky and use the DOF preview.
  • The textured pattern was/is not visible on <some other camera> probably because the viewfinder on that camera has lower magnification.
Does this help? BTW, you are really going to like your K-50. It is a fine tool and a pleasure to use.


Steve

Last edited by stevebrot; 10-02-2014 at 04:19 PM.
10-02-2014, 06:12 PM - 1 Like   #3
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Nothing wrong with it but if you want less of a pattern and want higher accuracy when doing manual focus (at the cost of viewfinder brightness with slow lenses) you can change to a modded Canon EES screen. The pattern is simply a result of the high magnification and bright viewfinder.
10-02-2014, 06:47 PM   #4
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QuoteOriginally posted by stevebrot Quote
This question comes up periodically and the answer usually involves one or more of the following tidbits:
  • In order to show the projected image, the focusing screen requires a matte/textured surface to scatter the light. All reflex viewfinders (the "R" in SLR) as well as focus system for view cameras share this requirement. This textured surface can be as simple as ground glass or as complex as a microscopic array of tiny prisms.
  • Your focus screen includes a Fresnel lens as part of its construction. It is there to make the screen brighter and to provide magnification. The Fresnel lens is made of a series of concentric ridged arcs. To see the pattern set your aperture at about f/8, point the camera at the sky and use the DOF preview.
  • The textured pattern was/is not visible on <some other camera> probably because the viewfinder on that camera has lower magnification.
Does this help? BTW, you are really going to like your K-50. It is a fine tool and a pleasure to use.


Steve

Very helpful. Thanks.
I think that my change to using a DSLR has me on a learning curve. My past experiences were clear, bright views from my old film based SLRs such as the K1000 and Minolta X-370. From what I have found out so far, the focusing screen on my K-50 is supposedly a Natural-Bright-Matte III. I looked around a bit, and found that there are replacement focusing screens, with different features such as split ring, but they are not cheap, and I may still be thinking in manual focus. I have not used an autofocus SLR before. Maybe I just need to get used to the view, and using AF.

I am quite happy to now know that my camera is fine. I must say that I simply love this K-50 of mine, even considering learning all this new-fangled digital stuff is.


QuoteOriginally posted by VisualDarkness Quote
Nothing wrong with it but if you want less of a pattern and want higher accuracy when doing manual focus (at the cost of viewfinder brightness with slow lenses) you can change to a modded Canon EES screen. The pattern is simply a result of the high magnification and bright viewfinder.
I saw a bit about swapping screens. Anything that makes it darker for me is a unappealing. KatzEye Optics has what looks nice, but is likely darker and not cheap.
Thanks.

I love this forum.

10-02-2014, 08:23 PM   #5
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QuoteOriginally posted by Schick Quote
the focusing screen on my K-50 is supposedly a Natural-Bright-Matte III.
Yes, that is what it is called. It is optimized for brightness, but has its weak points in regards to manual focus.

QuoteOriginally posted by Schick Quote
KatzEye Optics has what looks nice, but is likely darker and not cheap.
No, the KatzEye is not cheap, but with the optional OptiBrite treatment its brightness is on the same order as the screen on your K-50.* As for comparison to film SLRs, you can see the same thing on a K1000 screen, but it is less evident at f/2 (the maximum aperture of the kit lens) than at the maximum aperture range of your DA L 18-55/3.5-5.6 kit lens. There is another additional factor that is not immediately obvious. Your K-50 uses a partial-silvered main mirror as part of the AF system. The amount of light actually striking the focusing screen is somewhat less than with a film camera.


Steve

* I have been shooting with a KatzEye since 2008.
10-02-2014, 09:13 PM   #6
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QuoteOriginally posted by stevebrot Quote
Yes, that is what it is called. It is optimized for brightness, but has its weak points in regards to manual focus.



No, the KatzEye is not cheap, but with the optional OptiBrite treatment its brightness is on the same order as the screen on your K-50.* As for comparison to film SLRs, you can see the same thing on a K1000 screen, but it is less evident at f/2 (the maximum aperture of the kit lens) than at the maximum aperture range of your DA L 18-55/3.5-5.6 kit lens. There is another additional factor that is not immediately obvious. Your K-50 uses a partial-silvered main mirror as part of the AF system. The amount of light actually striking the focusing screen is somewhat less than with a film camera.


Steve

* I have been shooting with a KatzEye since 2008.
Thanks again. The KatzEye does look attractive. My lack of experience makes me wonder if the nice split ring will affect auto focus, or is made for mostly manual shooting.
10-02-2014, 09:52 PM   #7
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A different focus screen won't change autofocus accuracy. A non-Pentax screen won't have the same brackets which tell you where the grid of AF points are. So if you have gotten used to choosing an AF point (assuming this is even possible on the K-50) it may be harder.

People looking to improve manual focus look at two types of screens. The KatzEye is one of the split prism types. There are a few split-prism variations and more price points. Two big drawbacks with this type: spot metering is affected for certain lenses, though other metering types are fine. And the most precise focus is where the split is. The rest of the screen is pretty much like the stock screen. Some people also think the prism clutters up the viewfinder. The more expensive versions are less fussy about having your eye exactly centered on the prisms, and better with really slow lenses.

The other type is made from a Canon EE-S screen. It has no markings on it at all, taking care of the spot metering and clutter issue. The pattern on the screen is designed to make focus transitions really obvious for very fast lenses, like the f1.4 manual focus lenses from Samyang. The drawback is that slow lenses like an f4-5.6 zoom will have a darker viewfinder than with the stock screen. It's probably OK for most lenses you're likely to see. Mirror lenses, really long telephotos, teleconverters, or maybe slow macro lenses will not be easy to use, but you can get by.

You may have to adjust a focus screen for optimum focus, by putting shims in next to the screen.
10-03-2014, 08:18 AM   #8
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Thanks for jumping in. Here are a few more comments.
QuoteOriginally posted by Just1MoreDave Quote
A non-Pentax screen won't have the same brackets
Both KatzEye and focusingscreen.com offer various grids (including the AF brackets) at additional cost.

QuoteOriginally posted by Just1MoreDave Quote
spot metering is affected for certain lenses
My experience with the KatzEye is that spot metering is thrown off some with very fast lenses (f/2 and wider maximum aperture) and is basically non-functional at narrower apertures. This is a historic problem with split image focus screens going back 40+ years to the first SLRs offering spot metering.


Steve

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