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.