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Manual Focus Canon 10D

Readers of my dwainasaurus.blogspot.com articles might already know part of this story. A friend wanted a malfunctioning Canon 10D and BG-ED3 battery grip out of his sight and offered it for a song. Canon's dreaded Err99 had reared its ugly head and a digital body of this vintage doesn't usually justify Canon's repair costs.

The BG-ED3 grip, with the exception of normal wear, was fine so I knew the deal would have some value. After experimenting with the body for a short while I discovered that it generally only reported Error 99 when an EOS lens was attached. Using an M42 to EOS adapter I fount that fitting a non EOS lens (which does not communicate with the body via the EOS style electrical contacts) allowed the body to function without Err 99 codes coming up on the LCD display.

When non EOS lenses are used they work only in stop down metering mode. The camera only functions properly when the command dial points it to manual or aperture priority modes. And focusing with the smallish viewfinder can be challenging. But I pushed forward. Testing took place over the course of a couple outtings and decent images were created and used on the previously mentioned blog pages.

I researched aftermarket focusing screens including the ones offered by Katz Eye. If I had more confidence in this body I would have simply ordered one. Instead, in another 'Red Green' moment, I decided I could fashion my own.

Actually, 'cut down' is a more accurate description. Creating a focus screen wasn't the plan. Repurposing one was. The donor camera was a Minolta XG-A 35mm film camera. The focusing screen had a split prism circle and a microprism collar just like the aftermarket focusing screen offered by Katz Eye.

M42 adapted 10D shows its original focusing screen and shim.

The first step was to pop out the original screens and measure them. The Minolta screen was considerably larger as 35mm is a larger format than the APS-c sized sensor used in the 10D. There would be plenty of material available. Thickness was the next challenge and the screens were quite close. The Canon screen is backed by a metal shim. The combined thickness of the Canon screen and its accompanying shim was within one thousandth of the thickness of the Minolta screen. I measured the height and width of both and calculated how much the Minolta screen needed to shrink. The original Canon screen has a few bumps along its perimeter to help align it correctly. I didn't bother reproducing those bumps.

Cutting was tedious due to the tiny size of the screen. Final sizing was accomplished with a fine single cut file.

After popping the Minolta screen into the body I took a couple test shots to verify focus via the split prism circle produced 'in focus' images. Everything looked OK while chimping the LCD screen. Next up was a test with a Vivitar 135mm 1:2.5 T4 M42 screw mount lens. This lens would have relatively shallow depth of field and would be a more critical test of the focusing screens calibration. Viewing the images at full resolution on my monitor showed that the focus achieved by the split prism looked to be perfect.

During my research I found some users of aftermarket focus screens reporting exposure issues. My modified 10d seems to be OK although I haven't used it in enough situations to say for sure it is not affected.

At the end of these projects I usually look back and ask myself 'Why?'. The answer is pretty easy this time. I recycle. I derive enjoyment from recycling what would otherwise be garbage. To get viable images using parts from three different camera systems brings a smile to my face. Secondly, I miss shooting old school manual focus, manual aperture, manual film advance, 35mm cameras. I rediscovered that simple joy while shooting a Minolta X-370 recently. Shooting with the manual focus Canon 10d feels like a pretty similar experience to shooting the old school SLR's. And that is reason enough for me.