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04-03-2015, 09:55 AM   #1
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Adapting an old Split-Prism Focusing Screen for the Pentax K-x

Hello guys and girls,
the other day i was shooting what i thought were beautiful portraits at night with an SMC-M 50mm f/1.7 wide open and a Pentax K-x, and when i got home i found a bunch of out-of-focus pictures. I was really frustrated to having missed those shots, so i got inspired by a video about adapting a film-camera split-prism focusing screen, and next day i got my hands on the doing.
This is the video
, and the rest of the post is about the experience of doing it.

I got started dissasembling a Canon T60, taking out the pentaprism to acces the focusing screen (this model has not interchangeable focusing screens, so it must be accesed from the inside)
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Then i got the focusing screen out
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After removing the screen, i removed the K-x screen to measure its size, and draw it in paper to find its center so i could match it to the location of the prism-ring containing the split-prism in the CanonT60 screen. I secured it with scotch-tape and placed slide-glasses on both sides for protection.
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These were the tools: Tweezers, microscopy slideglasses, Cutter, and those black things which look like metal-butterflies that are used to holding glass.
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Next thing was to place the focusing screen in the camera, on top of the mirror, without the shims. After some manipulation, it got into place and i locked the slot in the viewfinder, and the focusing screen is doing its marvellous work with fast manual lenses, and it doesnt affect autofocus nor metering at all. It works quite great on tele lenses about 135mm, but regarding wide angles the split-prism shows an image a bit unaligned when in focus. Still i bare with it with the aid of focus-confirm though.
Well, that was all, i just wanted to share with the forum that this is possible in the Pentax K-x, and to hear if anyone else has tried adapting an old screen to fit a DSLR.
Regards from Uruguay

04-03-2015, 11:23 AM   #2
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QuoteOriginally posted by Bruno-C Quote
Well, that was all, i just wanted to share with the forum that this is possible in the Pentax K-x, and to hear if anyone else has tried adapting an old screen to fit a DSLR.
Thanks for sharing your experience! There are a number of users on this site who have cut down screens from old film cameras. In fact, I suspect that the video you shared was/is a forum member.

In regards to the split image being off a little relative to true focus. That can be adjusted by shimming the screen, but you must be confident that your reference for focus is accurate!


Steve
04-03-2015, 11:35 AM   #3
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Thanks Steve! I'll adjust the screen in the near future with the aid of a tripod and live view. Ahh and i'll try to find that forum member and thank him personally
04-03-2015, 11:39 AM   #4
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That is an interesting post I've just been pricing better view screens and I don't know if I want to support the Taiwan economy to that extent. D.D.

04-04-2015, 10:57 AM   #5
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That video inspired me to do the same thing a few months ago, too!
I asked in a facebook gear trading/selling group if anybody had an old broken SLR with a split screen that they didn't want anymore and got one for free. It was an M42 Petri 2 and while dissasembling it I realized that the defect was in fact a feature. As I literally had to destroy the camera to get to the focus screen, I felt a little guilt. The result is great, though. As far as I can tell, the focus in my K5 is accurate without any shimming at all. I guess I just got lucky. I can just recommend everyone to try it out, the method in the video is pretty straight forward. Even if it doesn't work out a 100%, you'll still have some fun while building it.
04-04-2015, 12:16 PM   #6
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QuoteOriginally posted by Arvid Quote
As I literally had to destroy the camera to get to the focus screen, I felt a little guilt.
Haha oh poor old camera that was so carefully manufactured! i have felt the same with mine! Ive dissassembled and repaired about ten digital cameras, but old film ones are so mechanically complex that are REALLY messy to work with!!! Great your screen worked perfectly! i'm about to calibrate mine in these days

QuoteOriginally posted by Arvid Quote
Even if it doesn't work out a 100%, you'll still have some fun while building it.
Definitely true! I know my pics aint the greatest, but i have waaay too much fun doing things myself

Kind regards!
11-10-2015, 08:26 AM   #7
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Thanks for this link and the moral support! I'm about to buy a junker camera for spare parts anyway, so I'm gonna take a shot at transplanting the screen into my K-x before I give up on it. I've had many of the same manual focus frustrations as you, Bruno. How is it working out now that a few months have passed?

11-11-2015, 11:00 AM   #8
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QuoteOriginally posted by jcdoss Quote
Thanks for this link and the moral support! I'm about to buy a junker camera for spare parts anyway, so I'm gonna take a shot at transplanting the screen into my K-x before I give up on it. I've had many of the same manual focus frustrations as you, Bruno. How is it working out now that a few months have passed?
Hi! I had been working better than the standard mate screen but not quite so good, so i again changed it with a great pentax split prism screen from a Film Pentax LX camera, then calibrated it (had a bit front focusing), and now it is really doing good on lenses from f2 to f4!
If you are going to buy a trashed camera only to use its focusing screen, i advise you to get a camera with interchangeable screens (it takes you seconds to remove the screen, instead of hours of fighting when the screen is a fixed one). Good Luck!
11-11-2015, 12:06 PM   #9
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It seems like a lot of work to manufacture a $20.00 split prism focus screen that's ready made and available on eBay...
11-11-2015, 03:19 PM   #10
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QuoteOriginally posted by Bruno-C Quote
If you are going to buy a trashed camera only to use its focusing screen, i advise you to get a camera with interchangeable screens (it takes you seconds to remove the screen, instead of hours of fighting when the screen is a fixed one). Good Luck!
Thanks! I've ordered an "as-is" Super Program for other reasons. If I can't get the screen out, I won't sweat it too much, as excanonfd said, screens are available online for 20 bucks. Question on that, though... if I'm going to use it in a K-x, is there any particular one that's compatible?
11-11-2015, 06:33 PM   #11
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QuoteOriginally posted by excanonfd Quote
It seems like a lot of work to manufacture a $20.00 split prism focus screen that's ready made and available on eBay...
It's not really that complicated or hard but you'll never get to experience it if you never try to do it. I guess this goes for a lot of things in life.
Why bother making your own pizza dough if you can buy it in a can from the supermarket? In the worst case you learn something new (for free).

I guess this is the right time to thank Bruno for the inspirational video: Thank you very much! I had the idea for some time, but seeing the video finally pushed me to try it on my own.
11-11-2015, 08:37 PM   #12
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Bruno-c went through 2 screens and even with calibrations afterwards, the screen is good up to f4.0 - those cameras where the focus screens were taken from, they weren't free were they? OTOH, the $20.00 eBay screen that was in my K20D way back when could accurately focus down to f8.0 - f11.0. It's all moot point now since I've parted company with the K20D and the eBay screen and moved on to a K-5 and a KatzEye split prism screen with Optibrite treatment.

@jcdoss,

Search for a split prism screen Pentax on eBay and order the appropriate screen for your camera.
11-12-2015, 01:37 AM   #13
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QuoteOriginally posted by excanonfd Quote
Bruno-c went through 2 screens and even with calibrations afterwards, the screen is good up to f4.0 - those cameras where the focus screens were taken from, they weren't free were they? OTOH, the $20.00 eBay screen that was in my K20D way back when could accurately focus down to f8.0 - f11.0.
In my case it was for free (ok, I bought a metro ticket to go and pick the camera up) and I used tools that I found at home. I might have gotten lucky, though, as I didn't have to do any shimming and it just seems to work fine, as I posted above a few months ago. And I had fun. Your mileage and definition of fun may vary, of course.

You could focus down to f11? The split prism didn't black out?
11-12-2015, 10:11 AM   #14
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QuoteOriginally posted by Donniealso Quote
That is an interesting post I've just been pricing better view screens and I don't know if I want to support the Taiwan economy to that extent. D.D.
In the global scheme of things given the $30 I paid for each of my focusing screens, what is the economic impact of every Pentax dslr user getting one at the time they get their camera? I doubt they would notice the change in GNP.

What is your time worth to bastardiZe an old camera and cut t down to size. I doubt you are breaking even in the deal. My time is worth more than the $ 30 I spent so actually buying one has the chance of improving our economy by doing more valuable work
11-12-2015, 11:54 AM   #15
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QuoteOriginally posted by Arvid Quote
In my case it was for free (ok, I bought a metro ticket to go and pick the camera up) and I used tools that I found at home. I might have gotten lucky, though, as I didn't have to do any shimming and it just seems to work fine, as I posted above a few months ago. And I had fun. Your mileage and definition of fun may vary, of course.

You could focus down to f11? The split prism didn't black out?
In a good light, half of the split prism does start blacking out but using the micro prisms encircling the split prism, I was able to get some acceptable shots but stacking multiple TC results in unacceptable loss of IQ which made that experiment redundant. Sorry, I lied it was f9.52 (or was it f10.36?) - Tamron Adaptall-2 300/2.8 + Pentax AFA 1.7x + Tamron 2x TC.
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