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07-08-2017, 01:53 PM   #1
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How fragile is a K70 pentaprism?

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Hi there, I hope I haven't cracked the pentaprism in my fairly new K-70... I decided to clean up some dust that was becoming noticeable when using the K-70 viewfinder. I used a very soft cloth and VERY LIGHTLY rubbed the mirror and pentaprism surfaces. Much to my surprise a very dark diagonal line showed up on the lower right quadrant of the viewfinder - looks a bit like a thick, black strand of hair. I've cleaned both surfaces in the same way before and never had this dark hairline show up.

Upon closer inspection, I can see the same line on the pentaprism inner surface (it looks lighter and thinner, but it is definitely the same line given its position and shape). I'm wondering if I may have cracked the pentaprism surface (although I thought the pentaprism was a beefy hunk of glass), or if anybody out there has had a similar experience and what was done about it.

The line doesn't affect the pictures at all, it doesn't show up in live view but it really bugs me! I can imagine it will cost me a small fortune if I have to send the K-70 in for repair.

Any helps is appreciated - thanks!

07-08-2017, 02:22 PM   #2
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I think you may have scratched the focus screen. I believe it is a very soft plastic and can be scratched easily, and it's actually the focus screen you are looking at there, not the pentaprism surface.
07-08-2017, 02:23 PM   #3
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Correct, unless you removed the focusing screen then you didn't touch the prism. The screen can be replaced at a service center.

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07-08-2017, 02:27 PM - 4 Likes   #4
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QuoteOriginally posted by mmbrombe Quote
I decided to clean up some dust that was becoming noticeable when using the K-70 viewfinder. I used a very soft cloth and VERY LIGHTLY rubbed the mirror and pentaprism surfaces.
The underside of the pentaprism is normally not exposed for you to clean. The line you see is likely a scratch on the underside of the focusing screen.

First rule of camera cleaning for amateurs:
Use extreme care with or better yet, do not touch the mirror.
The surface of the mirror is VERY fragile and abrades very easily. Scratches may affect both the viewfinder image as well as AF performance. Rubbing with a cloth or similar may also affect mirror alignment with serious consequences for AF performance. Replacement requires the skills of a repair technician ($$$). Remove dust with a puff of air from a bulb-type blower.

Second rule of camera cleaning for amateurs:
Never touch the surface of the focusing screen unless you are absolutely sure you are prepared to replace it.
The focus screen is made out of plastic and the micro-textured underside is very fragile. Do not touch. Do not use devices or products designed for lens cleaning on the screen. Remove dust with a puff of air from a bulb-type blower.

Third rule of camera cleaning for amateurs:
Never use canned or compressed air on your camera.

Assuming the line is a scratch, the screen is user-replaceable and costs about $35 for the Pentax-brand replacement. Doing the replacement requires a special tool to set the screen, steady hands, good eyesight, and attention to keeping the work area dust free while doing the transplant. Removal of dust from the area between the focus screen and the underside of the pentaprism can be difficult. A repair shop can also replace the screen for a nominal charge.

You may also choose to leave well enough alone. I have a couple of old film cameras whose screens are marred. Parts are unavailable, so I live with it.


Steve


Last edited by stevebrot; 07-08-2017 at 02:51 PM.
07-08-2017, 05:35 PM   #5
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Hopefully you only touched the focusing screen, as this is easily replaced. Generally speaking, you should really never touch the focusing screen or the inside of Pentaprism. Simply because these surfaces must be really really clean. A few dust spots is not a problem, but fingerprints, skin oil, things like that are much more bothersome. Similarly with the mirror. You only want to clean the inside of the camera with dust rocket blower, a Pentax static "lollipop" remover, or liquid cleaning. Liquid cleaning is advanced, you should only use trusted brands, do it correctly, follow the instructions, and also only use one brand in a given camera. I heard that some brands can leave residue that can cause problems if you later use another type of liquid cleaner. At least, that is what a repair shop told me..

Some great posts above. You can also search online for blog posts or youtube videos that have a lot of info about this.

The focusing screen is probably the most fragile piece there, but you can find third party screens online, with a DIY replacement kit, or you can just have a shop do it
07-08-2017, 08:09 PM   #6
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Did it look like this?
Dust in Focus Screen - PentaxForums.com

The focus screen was actually easy for me to clean. I could make a short video on how I did this, because I couldn't find a straight forward video on how to clean a Pentax focus screen. The long and short:

Flip your camera upside down. On the top of the camera, where there is a gap in the light seal foam, there is a small latch. Give a small tug to the latch. The latch let's go of the focus screen's holder. The holder doesn't need to be moved much. Just use a rocket blower (never use compressed air) to blow out the dust/ hair. Press the holder back into the latch (make sure the screen is put back in the same position on the holder, too).

Really, I should just make a short video..
07-09-2017, 09:11 AM   #7
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Thanks everybody for the tips and insights, much appreciated. Wish I knew all this BEFORE I tried it. I guess I can live with the ugly line for now, seems like my concern is if I misaligned anything. I will take some test shots to verify focus. Thanks again.

05-12-2022, 08:33 AM - 1 Like   #8
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QuoteOriginally posted by FozzFoster Quote
Did it look like this?
Dust in Focus Screen - PentaxForums.com

The focus screen was actually easy for me to clean. I could make a short video on how I did this, because I couldn't find a straight forward video on how to clean a Pentax focus screen. The long and short:

Flip your camera upside down. On the top of the camera, where there is a gap in the light seal foam, there is a small latch. Give a small tug to the latch. The latch let's go of the focus screen's holder. The holder doesn't need to be moved much. Just use a rocket blower (never use compressed air) to blow out the dust/ hair. Press the holder back into the latch (make sure the screen is put back in the same position on the holder, too).

Really, I should just make a short video..
Hello mate!
I have the same mess on my 2 months old k-70's like on that picture of yours.
Did you make the video? I could follow your instructions, but i am afraid i can brake something and lose warranty, but if there's not video, i will take a risk anyway.
Best Regards
Adam
05-12-2022, 10:02 AM   #9
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QuoteOriginally posted by penotax Quote
Did you make the video?


Different camera, exact same process.
Once you get the screen out you can use a rocket blower to get the dust out

Best luck!
05-12-2022, 07:35 PM - 1 Like   #10
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QuoteOriginally posted by FozzFoster Quote
https://youtu.be/l5xLU6JDyKk


Different camera, exact same process.
Once you get the screen out you can use a rocket blower to get the dust out

Best luck!
Thank you so much mate
Best Regards
Adam
05-12-2022, 11:29 PM - 1 Like   #11
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Well explained how to change the focusing-screen also here:
--Pentax K1/K1II/K3/K5/K7/K10D/K20D/K30/K50/K70/ISTD/K-S1/K-S2/KP Focusing Screen Installation Instruction--

If you want to replace it, got for the Pentax ML60, a bit more expensive but I like it better.
pentax ml60: Search Result | eBay

The f.screens of the Pentax K7/5/3/KP, K30/50/500 K-S1/2 and K70 are all identical.
05-13-2022, 09:46 AM   #12
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QuoteOriginally posted by photogem Quote
The f.screens of the Pentax K7/5/3/KP, K30/50/500 K-S1/2 and K70 are all identical.
I didn't know that! Thanks for the tip
05-13-2022, 11:42 PM   #13
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no success

Hello again!
I took out the focusing screen and cleaned it using a rocket blower and it's got worse, I took it out again and did the same thing and it's got even worse.
I fully charged the battery, exposed the sensor and used the rocket blower and checked it again, nothing has changed.
Then I took a few pictures with small aperture - the pictures are clean
So, the focusing screen is not dirty, nor the sensor, any idea what it could be?
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05-14-2022, 05:18 AM - 1 Like   #14
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QuoteOriginally posted by FozzFoster Quote
I didn't know that! Thanks for the tip
After further inspection with a magnifier, i found out that i ****ed up the focusing screen,
No further advices required.
Best Regards
Adam
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