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08-18-2012, 12:18 PM - 1 Like   #1
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Custom K20D Focusing Screen

After trying really hard to master manual focusing by using the focus confirmation light only, I finally decided it wasn't possible to get an acceptable and reliable accurate-focus rate by just relying on that system. Something had to be done about it.

Ordering things from abroad is a really tedious task here in Argentina, hence, buying a chinese focusing screen was out of the question. So, after reading some threads about people cutting their own screens, I decided to give it a try.

I had an old Canon T50 lying around, which is supposed to have a very good focusing screen, the same used for the AE-1 Program and the nF-1. Bad news was that the T50 does not have a removable focusing screen, so I had to completely take apart the top part of the camera, where the pentaprism is located in order to reach the screen. Of course the poor Canon is now out of order, but it served a good purpose. Plus, I get to keep a nice pentaprism for my desk.

I have to admit I didn't take enough safety measures in order to keep the screen clean and free of scratches since all the procedure was pretty much improvised, but after the abuse that focusing screen went through during the cutting process, I have to say that these pieces of plastic are tougher than people say they are.

Cutting was done through scoring each line with a razor knife, and then snapping the borders out. Borders were then smoothed using a nail file. During this whole process, dust and some heavy uncareful handling left some minor marks on the focusing screen, really nothing to worry about. In the pictures it may seem that the screen is pretty damaged, but one's really not aware of those marks when focusing so, no big deal. I'll admit, if I had to do it again, I'd protect the surface with some kind of tape, but I didn't do this because I was worried it would leave some kind of residue.

In my opinion, the most important part of the whole process is good and careful measuring. I spent about an hour or two making sure everything was in place before I started cutting.

Once the worst part was finished, I proceded to clean using warm tap water and soap. Yeah, the screen looked pretty busted at this stage, so I didn't care a lot at that point, but after gently washing it and seeing that it wasn't that bad, I felt a little more satisfied with the results.

Focusing screen was installed on my K20D without any kind of trouble and so, testing begun. At first, a little bit of front focusing was the issue, so I removed the shim originally placed in the camera for the stock screen. After this, I perceived a more severe case of back focusing. I reduced the shim thickness by grinding it against a knife sharpening stone. After placing the shim, a little bit of front focusing was still present, but at this moment I had already spent nine hours working on that screen and I was tired, so I decided to leave it like that. Maybe I'll revise it again in the future if I get imprecise results while shooting out in the real world.

And here's what you all wanted to see... the results.

As you can see, the screen is pretty busted, all scratched and kinda' dirty. Nothing that will distract you or get in your way while shooting. Focusing now is easy and actually pretty fun.

Out of focus.


Focus placed on the blue pencil.


And this is the picture taken with the K20D when focusing on the blue pencil. Lens used was a Pentax-A 50mm 1.4 shot wide open.


So far, the slowest lens I tested the screen with is a 28mm 2.8 and, even in the darkest room of my house at night I couldn't get the split screen to black out. I remember the T50 suffering from split screen black out from time to time, mainly in interiors, but I'm sure it was due to the very slow kit lens it had mounted on.

Focus confirmation light still comes in handy. It lights up and beeps right when I get the split screen aligned.

The only minor detail is that I had to dial in a +1.0 exposure compensation due to metering errors, but that was only expected since the screen is a little brighter than the stock one.

I'm extremely happy with the results and the confidence I used to feel when shooting with my Pentax MX is back.

Cheers and thanks for reading.


Last edited by J. Angera; 02-04-2013 at 07:42 AM.
08-18-2012, 12:50 PM   #2
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Nice!
I have been considering ordering one of the chinese replacement focusing screens for my K10D, but have been delaying the decision because I am not sure about the quality of the generic ones, and branded screens seem to expensive. Also, here in Chile, while not so much of a hassle, chinese stuff takes forever to arrive, usually around 2 months.
Might give this method a try if I find a dead SLR to cannibalize.

EDIT: I just re-read your post, and: The replacement screen is actually brighter than the stock one? Or is that a typo? If not, this seems like a no-brainer.
08-18-2012, 01:44 PM   #3
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Using such bright apertures, it should be brighter...use a 5.6 lens and you've got a problem...
08-18-2012, 01:48 PM   #4
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QuoteOriginally posted by c-meier Quote
The replacement screen is actually brighter than the stock one? Or is that a typo? If not, this seems like a no-brainer.
I'm not really able to compare side to side both of the screens to make an objective comparison, and honestly, I don't remember the stock one being darker... but the light meter underexposing led me to think that the new screen is actually brighter.

08-18-2012, 01:52 PM   #5
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QuoteOriginally posted by GabrielFFontes Quote
Using such bright apertures, it should be brighter...use a 5.6 lens and you've got a problem...
Hehe, well, none of my lenses are that slow luckily, so I think I'm pretty much safe for now. But as I said, I'm pretty sure it would black out at smaller apertures like it used to happen with the Canon zoom lens.
01-26-2013, 10:36 AM - 1 Like   #6
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exposure issues?

QuoteOriginally posted by J. Angera Quote
After trying really hard to master manual focusing by using the focus confirmation light only, I finally decided it wasn't possible to get an acceptable and reliable accurate-focus rate by just relying on that system. Something had to be done about it.

Ordering things from abroad is a really tedious task here in Argentina, hence, buying a chinese focusing screen was out of the question. So, after reading some threads about people cutting their own screens, I decided to give it a try.

I had an old Canon T50 lying around, which is supposed to have a very good focusing screen, the same used for the AE-1 Program and the nF-1. Bad news was that the T50 does not have a removable focusing screen, so I had to completely take apart the top part of the camera, where the pentaprism is located in order to reach the screen. Of course the poor Canon is now out of order, but it served a good purpose. Plus, I get to keep a nice pentaprism for my desk.

I have to admit I didn't take enough safety measures in order to keep the screen clean and free of scratches since all the procedure was pretty much improvised, but after the abuse that focusing screen went through during the cutting process, I have to say that these pieces of plastic are tougher than people say they are.

Cutting was done through scoring each line with a razor knife, and then snapping the borders out. Borders were then smoothed using a nail file. During this whole process, dust and some heavy uncareful handling left some minor marks on the focusing screen, really nothing to worry about. In the pictures it may seem that the screen is pretty damaged, but one's really not aware of those marks when focusing so, no big deal. I'll admit, if I had to do it again, I'd protect the surface with some kind of tape, but I didn't do this because I was worried it would leave some kind of residue.

In my opinion, the most important part of the whole process is good and careful measuring. I spent about an hour or two making sure everything was in place before I started cutting.

Once the worst part was finished, I proceded to clean using warm tap water and soap. Yeah, the screen looked pretty busted at this stage, so I didn't care a lot at that point, but after gently washing it and seeing that it wasn't that bad, I felt a little more satisfied with the results.

Focusing screen was installed on my K20D without any kind of trouble and so, testing begun. At first, a little bit of front focusing was the issue, so I removed the shim originally placed in the camera for the stock screen. After this, I perceived a more severe case of back focusing. I decided to get creative and reduced the shim thickness by grinding it against a knife sharpening stone. After placing the shim, a little bit of front focusing was still present, but at this moment I had already spent nine hours working on that screen and I was tired, so I decided to leave it like that. Maybe I'll revise it again in the future if I get imprecise results while shooting out in the real world.

And here's what you all wanted to see... the results.

As you can see, the screen is pretty busted, all scratched and kinda' dirty. Nothing that will distract you or get in your way while shooting. Focusing now is a breeze and actually pretty fun.

Out of focus.


Focus placed on the blue pencil.


And this is the picture taken with the K20D when focusing on the blue pencil. Lens used was a Pentax-A 50mm 1.4 shot wide open.


So far, the slowest lens I tested the screen with is a 28mm 2.8 and, even in the darkest room of my house at night I couldn't get the split screen to black out. I remember the T50 suffering from split screen black out from time to time, mainly in interiors, but I'm sure it was due to the very slow kit lens it had mounted on.

Focus confirmation light still comes in handy. It lights up and beeps right when I get the split screen aligned.

The only minor detail is that I had to dial in a +1.0 exposure compensation due to metering errors, but that was only expected since the screen is a little brighter than the stock one.

I'm extremely happy with the results and the confidence I used to feel when shooting with my Pentax MX is back.

Cheers and thanks for reading.
I did same thing with a screen from a bust Pentax ME super. I have been pleased with the results focus wise, and like you I looked at how it responded indoors and saw no issues.

But now I have been out with a couple of M42 lenses (tak 55mm, helios 58mm) on a bright day and exposure was way out: I was having to jump from Av to M to adjust by more than 3 stops and keep checking the exposure on the histogram.

So I wondered how you have found yours since ...
01-26-2013, 11:40 AM   #7
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Nice. I was thinking of doing the same mod to my K20D, but am not sure of spending ~$100 on one (Katz Eye). I don't have any M42 lenses, so I don't think aperture blackout would be a problem since my M 50mm f/1.7 stays wide open regardless of where I have the aperture set. It only closes when I press the shutter. I assume this works the same for all M lenses and other old third party K-mounts?
01-26-2013, 08:45 PM   #8
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QuoteOriginally posted by marcusBMG Quote
I did same thing with a screen from a bust Pentax ME super. I have been pleased with the results focus wise, and like you I looked at how it responded indoors and saw no issues.

But now I have been out with a couple of M42 lenses (tak 55mm, helios 58mm) on a bright day and exposure was way out: I was having to jump from Av to M to adjust by more than 3 stops and keep checking the exposure on the histogram.

So I wondered how you have found yours since ...
Can you explain "I did same thing with a screen from a bust Pentax ME super" that means the one in the ME Super can be cut to make if a split focus screen for a K20D?

If this is true, I have one broken ME Super with the Focusing screen in good condition that I can try it out.

Thanks in advance for your reply.

01-27-2013, 06:29 AM   #9
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QuoteOriginally posted by NitroDC Quote
Nice. I was thinking of doing the same mod to my K20D, but am not sure of spending ~$100 on one (Katz Eye). I don't have any M42 lenses, so I don't think aperture blackout would be a problem since my M 50mm f/1.7 stays wide open regardless of where I have the aperture set. It only closes when I press the shutter. I assume this works the same for all M lenses and other old third party K-mounts?
Note that the K10D and K20D have some really bad metering with manual lenses. There have been a lot of threads on this topic

See the attached chart



You need to test using a uniformly lit surface, (block wall, paved road, etc) and correct accordingly.

Although exposure seems all over the map it is predictable and consistent for each lens and usually each FStop regardless of lens focal length
01-30-2013, 12:17 PM   #10
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QuoteOriginally posted by marcusBMG Quote
I did same thing with a screen from a bust Pentax ME super. I have been pleased with the results focus wise, and like you I looked at how it responded indoors and saw no issues.

But now I have been out with a couple of M42 lenses (tak 55mm, helios 58mm) on a bright day and exposure was way out: I was having to jump from Av to M to adjust by more than 3 stops and keep checking the exposure on the histogram.

So I wondered how you have found yours since ...
Just to make sure, you are not trying to shoot in any aperture other than wide open while using the AV mode, right? Even in that case, you shouldn't have to switch to M to make exposure compensations in AV, since you can do this with one of the control wheels (I use the front one in my K20D), provided of course you're still shooting wide open.

Anyway, about your question... when I shoot with my 50-A, I find myself doing a lot of exposure compensation while in AV mode. It's well known that manual lenses tend to underexpose as the aperture gets smaller. I just got used to it and I'm continuously adjusting the compensation, specially in places with variable light conditions where I switch my apertures a lot.

But then again, it has nothing to do with the focusing screen, it's just the way manual lenses work on dSLRs.
01-30-2013, 04:28 PM   #11
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QuoteOriginally posted by jjdgti Quote
Can you explain "I did same thing with a screen from a bust Pentax ME super" that means the one in the ME Super can be cut to make if a split focus screen for a K20D?

If this is true, I have one broken ME Super with the Focusing screen in good condition that I can try it out.

Thanks in advance for your reply.
Yes thats exactly what I did. The screen is plastic and I refer you to the review I wrote ( see accessories section) where I basically said what I did.


J. Angera:
With the M42 lenses I was trying to focus wide open and then stop down. There is no physical aperture connection to stop that so the idea is that in Av mode the exposure will auto adjust. Thats the way I operate with all MF lenses on my MFT G1. Wide open I was getting eV readings more than 3 stops out: 1/6000 shutter when 1/800 was required Can't compensate for that - only up to 3 stops. Thats why I was saying I was having to switch to M to spin the dial and shutter speed down. But my suspicion is that the metering is being jiggered by the centre prism, evemn though centre weighted isn't supposed to be too badly affected.
I am still working with it for the mo - i'll let you know how I get on. I think my next step is to put the standard screen back in and compare using that with the helios and takumar (which I'm very pleased with BTW helios might even be a bit sharper than the tak).

Lowell Goudge: Very interesting graph. Is the k-r similar?

Last edited by marcusBMG; 01-30-2013 at 04:31 PM. Reason: response to Lowell Goudge
01-30-2013, 04:55 PM   #12
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QuoteOriginally posted by Lowell Goudge Quote
Although exposure seems all over the map it is predictable and consistent for each lens and usually each FStop regardless of lens focal length
Just to clarify:: there is an exposure curve for each lens on each camera/screen combo, but that curve is consistent and predictable? So if there was a way of preprogramming the camera...
01-30-2013, 07:03 PM   #13
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QuoteOriginally posted by marcusBMG Quote
Just to clarify:: there is an exposure curve for each lens on each camera/screen combo, but that curve is consistent and predictable? So if there was a way of preprogramming the camera...
Correct, the performance is predictable, but unfortunately without knowledge of the aperture range (done through the pins on an A lens) it can't be programmed out. That's why thenK10/20 work well with A and later lenses, but not K and earlier. They programmed the non linearity of the screen out by using specific adjustment values based on maximum aperture (because that's where metering happens)
01-30-2013, 07:56 PM   #14
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QuoteOriginally posted by marcusBMG Quote
Yes thats exactly what I did. The screen is plastic and I refer you to the review I wrote ( see accessories section) where I basically said what I did.


J. Angera:
With the M42 lenses I was trying to focus wide open and then stop down. There is no physical aperture connection to stop that so the idea is that in Av mode the exposure will auto adjust. Thats the way I operate with all MF lenses on my MFT G1. Wide open I was getting eV readings more than 3 stops out: 1/6000 shutter when 1/800 was required Can't compensate for that - only up to 3 stops. Thats why I was saying I was having to switch to M to spin the dial and shutter speed down. But my suspicion is that the metering is being jiggered by the centre prism, evemn though centre weighted isn't supposed to be too badly affected.
I am still working with it for the mo - i'll let you know how I get on. I think my next step is to put the standard screen back in and compare using that with the helios and takumar (which I'm very pleased with BTW helios might even be a bit sharper than the tak).

Lowell Goudge: Very interesting graph. Is the k-r similar?
Thanks Marcus.
01-31-2013, 05:45 AM   #15
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QuoteOriginally posted by marcusBMG Quote
Lowell Goudge: Very interesting graph. Is the k-r similar?
I have no idea. I don't own one, and I could never get forum members, except for Bende8 to assist in checking other cameras as I didn't have a K5 at the time.

If you have a k-r and a 50/1.4 I would love to see the results. I use a cement block wall at the back of my house, or my driveway, as the uniform color, uniformly lit surface. Take the shots in JPEG with all settings neutral.
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