Further discussion about this little project is over at "that other place" at the URL: http://www.rangefinderforum.com/forums/showthread.php?t=25305 History: I love the Canonet QL17 GIII. However, it's not ideal. One shortcoming that has always bothered me was the limitation of ASA/ISO 800 as the fastest film that could be used with its internal meter. Since the GIII is one of my primary low-light cameras, this is of great importance to me. The one question which was brought up when I first mentioned the idea of the recalibration in some on-line forums (fora?) was that of the adequate range of sensitivity in low light conditions to properly work with 1600 speed film at the slower hand-held speeds. A quick check at ASA/ISO 800 at 1/4 second (two speeds slower than I ever expect to use hand held) showed that yes, the meter was responding to light of that level. The intended procedure is to perform a "two-point calibration" where adjustments (if needed) are performed on both the low ends and the high ends of the scale. This is similar to the "zero and span" calibration common on clincal laboratory equipment. Test equipment: I do not possess any test equipment whose calibration can be traced to any established standard. The closest I have is the meter in the Pentax K1000, a camera which over the years has consistently given good exposures on both print and slide film under daylight and artificial light conditions. Two light sources are used, a blank (eggshell, neutral, but slightly warm) bathroom wall with both the overhead lights and vanity lights on dimmers, and an east-facing window overlooking a grove on the edge of a forest preserve. Depending on the exact conditions, this gives exposure readings of 1-2 stops less than pure "sunny 16" conditions. Sanity check: The very first test was a "sanity check" on both the GIII and the Pentax using the existing batteries of both, the age of which are unknown or long forgotten. ISO 400 daylight 250 f8 250 f11 Canon ~1 stop under ISO 400 avail light 15 f2.8 15 ~f2.5 Canon slightly over This is similar to what I remember the last comparison to be, with the Canon slightly underexposing at the high end of the scale and overexposing slightly at the low end of the scale. The next part of the test was to install fresh batteries in both of the cameras in order to eliminate the variables of unknown battery age and condition. I've always used the "wrong" newer 1.5 volt 625 battery in the Canon. That was in the camera when I bought it, and even with the wrong battery it's always agreed within one stop of the Pentax under both bright and dim conditions. As could be expected, the response of the meter with this approximately 15% overvoltage was "hot", meaning greater span than normal, which is reflected by the high meter readings under bright conditions and the low(er) meter readings under dim conditions. ISO 400 daylight 250 f8-11 250 f11-16 Canon ~1 stop under ISO 400 avail light 15 f2.8 15 ~f2 Canon 1 stop over With fresh batteries, the difference of the Canon to the Pentax is slightly greater, indicating a possible partly depleted battery in the Canon. Procedure: The indended steps for this recalibration are as follows: 1. Disassemble the top part of the Canon. 2. Set the Canon ASA/ISO to 200, corresponding to ISO 400 film. 3. Mechanically adjust the meter on the Canon so the meter indicates f2.8 to agree with the Pentax using the low light test source. 4. Electrically adjust the meter on the Canon so the meter agrees with the Pentax using the bright light test source. 5. If necessary, repeat steps 3 and 4 as required. 6. Re-assemble and shoot test rolls. The first step is to remove the ring on top of the film advance lever. Many claim that this can be done by hand using a rubber jar opener or a rubber washer for grip, however, when I first got the camera and needed to take the top off, I could not get this to budge. I carefully drilled two small indentations in the ring for a spanner wrench. Once the advance lever and hardware are removed, the rewind crank is removed by holding the inside of the film rewind shaft and unscrewing the crank. Removing three small screws allows the top cover to be removed. On the first attempt, I failed to locate the screw that allows the mechanical re-adjustment of the meter for the low or zero setting. Instead I just adjusted the electrical adjustment at the high end of the scale. I made several back and forth adjustments, comparing the effect of the adjustments on the high and low ends of the scale. It was very obvious that the electrical adjustment had far more effect at the high (bright) end of the scale. I decided to split the error somewhat between the high and low ends of the scale. I settled on a setting that resulted in approximately a 1/2 stop underexposure at the high end (bright) of the scale and about a 1 stop overexposure at the low (dim light) end of the scale. This leaves at most a one stop error on the low end, and that is in the direction of overexposure, which I consider to be a lesser evil than underexposure when dealing with low light situations. After recal Pentax Canon (@ISO 200) ISO 400 daylight 250 f8-11 250 f11 Canon ~1/2 stop under ISO 400 avail light 15 f2.8 15 ~f2 Canon 1 stop over Note that the readings on the GIII are with the ASA/ISO set to 200, for a true ISO of 400, adjusted for the one-stop intentional miscalibration. The obvious next step is to shoot some test rolls under real-world shooting conditions. First, a sanity check roll of ISO 200 (camera set to 100) and next a roll of 1600 to test the end result of this procedure. Upon studying some online photos of the GIII, I was able to locate that elusive screw and perform the mechanical calibration at the low end of the scale. Although the elusive screw can be seen after the top cover is removed, loosening this screw actually requires further disassembly, the removal of the film counter assembly. Once this is done, a thin screwdriver may be used to loosen the screw, allowing the meter assembly to be rotated. First, the top cover of the camera is removed as described above. Next, the film counter indicator dial is removed by first removing one screw and sliding the dial off. This leaves the film counter assembly exposed and ready to be removed. Three items must be un-done in order to remove the two pieces of the film counter assembly: 1. A "clip ring" which holds the outer film counter wheel to the shaft under the film advance lever. This is tricky. I got this off carefully with two very small screwdrivers. Be careful to avoid letting this snap loose and fly across the room! 2. A screw post which holds one end of the film counter spring. 3. A screw opposite the post holding the spring. This is longer than it first looks and also holds the camera strap bracket in place. Once the elusive screw is exposed, apply a bit of nail polish remover to the lacquer holding it in place. After the remover has softened the lacquer, the screw may be loosened with a small screwdriver. Rotating the meter assembly is tricky. I used a combination of a dental explorer (that pick a dentist uses on your teeth) and a hemostat (a serrated surgical clamp) to gently coax the assembly one way or the other as needed. I adjusted my low light source to indicate an exposure of 1/15 at f2.8 ay ISO 400 on the test camera. You can use any test source of similar brightness, measured with a meter or camera that is known to be accurate. REMEMBER TO SET YOUR QL17 ASA/ISO TO HALF THE ISO OF YOUR METER OR TEST CAMERA! Rotate the meter assembly until the reading agrees with that of your test camera or meter. It's best to repeat the reading several times, capping the lens and allowing the meter to re-indicate the exposure. When this meter consistently agrees with your test camera or meter, tighten the elusive screw and proceed to the high brightness calibration. My known good camera read right between f/8 and f/11 at 1/250 at ISO 400. You can use any scene or light source somewhere in this range. Adjust the electrical adjustment (potentiometer) until the reading on the QL17 agrees with that of the known good camera when metering the bright scene. It can be tricky to adjust this, but a dental explorer in the "dimple" of the adjusment arm of the potentiometer moves it easily. Again, take several readings, capping the lens in between, and make the meter re-indicate each time. When you're satisfied that the QL17 reads the same as your known good camera, you can proceed to re-check the low light reading. You will find that the electrical adjustment affects the readings at the bright end of the scale far more than those at the dim end of the scale. The mechanical adjustment affects both readings equally. Therefore, the mechanical adjustment is used at the low end and the electrical at the high end. You may very well find that even after the electrical adjustment, the available light low end reading still agrees very closely. If this is the case, no further adjustments are necessary. If they do not agree, loosten the elusive screw again and repeat the low end adjustment. Then check/adjust at the high end, then the low end, rinse, repeat! After second recal Pentax Canon (@ISO 200) ISO 400 daylight 250 f8-11 250 f8-f11 On the numbers! ISO 400 avail light 15 f2.8 15 ~f2.8 Very close! As you can see, the Canon now agrees well within 1/2 stop of the Pentax under both dim and bright light. The final step after assembly was to paint a very conspicuous red dot by the ISO setting. This serves as a reminder, a "string around the finger" so to speak, to set the ISO to half of the actual film speed.