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35mm, 85mm, Balda, Baldinette, Canon, CdS, hack, Kopil, L-398, light meter, M42, meter, Sekonic, solar cell, spot, TTL
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I had to use my way back time machine to remember where and why I got the main part for this one day project that took a year to complete. About 15 years ago I was hot to trot over macro photography. I picked up this Kopil CdS TTL Meter at the time from a local, now out of store front business, shop. The idea for the usage by the manufacturer was to market a device to accurately read the reflected light off a small object through the actual lens to be used. Take the reading, transfer it to the camera, attach the lens to the camera and take a perfectly exposed image. Well, it would probably have worked, except, as is the case for most older CdS devices, the CdS cell was kaput*. So, it found its way to the junk drawer.
Every few years I would find it, look at it, consider what to do with it, and drop it back in. The batteries are too expensive to buy one just to prove it was kaput*.
About a year ago, it again found itself in my hand and I had a thought. If I were to go to the dollar store, buy four or five of those solar calculators, and strip out the photocells, maybe I could use them to power the meter. Off to the $ store, home with the calculators, strip out one of the cells, prove it changed voltage when the light level changed. Pack it all in a plastic bag and hang it on the doorknob to take to the workshop. Fast forward to yesterday, I found the bag still on the doorknob.
Unlike the past, I grabbed the bag, went to the shop and started the long overdue conversion. First, I removed the other four solar cells from the calculators. Using a DVOM, I checked the voltage of them all, they were very close to each other. Then I stripped out all the guts of the Kopil unit. The only parts I saved were the meter assembly and the case. Everything else went in the trash can. A couple of minutes were spent soldering in new wires to the meter as the old ones were falling apart. The inside of the Kopil would accept three of the solar cells side by side. They were then glued to a piece of thin cardboard that had been cut to just fit inside. To prevent damage to the solar cells, I found an old 82A Series 6 filter that just fit inside the case and glued it just short of the M42 threads. Then the cardboard with the cells, soldered in series, were glued inside. A quick check to make sure the meter moved when aimed at a light and the meter assembly was screwed back in place.
Now the fun part of any hack, to find out how to make it usable. First, I tried screwing it on the end of an old Tamrom zoom lens with M42 mount. Nope, not enough light was getting through the old lens. I had hoped for a variable focal length spot meter, but it wasn’t to be. Then I tried it with a 50mm lens. Lots of movement, but clunky to hold and carry.
OK, since it was an M42 screw mount, I tried varying lengths of M42 macro tubes. Looks like this might work. I grabbed my Canon XTi, which happened to have a Canon f1.8 85mm lens on it and headed to the window (31F outside). I was getting close to matching the XTi meter when I hit upon f4.5 and ISO 100. This sounded good as the whole idea of doing this was to use it with my 80-105mm lenses from old folding cameras on my Canon film AE-1 and the Balda Baldinette 35MM folding camera from ~1950 that is on its way. 35mm film in ISO 100 is easily found.
When I hit upon the Kopil meter’s setting of 1200 ASA with a 21mm macro tube attached – Bingo! Everything I aimed at was pretty much spot on according to the camera’s metering. Success! Remember that the meter and the settings on the dial were never meant to be used with three photo cells in series from a calculator. This was just dumb luck I did not have to fabricate settings on the dial head.
I now have a hacked semi spot meter (85mm focal length) which needs no batteries. I can leave it in the photo kit and use it as I need it without heading to the drug store. Outside, I aimed the hacked meter and the XTi at snow covered grass, the siding of my house, the shaded side of my car, a tree line landscape, a brick sided building 120 yards distant, a house in the Sun 200 feet distant and a concrete sidewalk out of direct lighting and all were within reason. I remember trying the same thing with my $200 analog Sekonic L-398 Studio Deluxe meter and never getting even close! Perhaps the next hack will be the same thing with the Sekonic, it is useless for general photography as it is, hmmmmmmmm.
*Kaput: useless, not functioning, junk, crap, etc.
