“QL” is for Quick Load
The “QL” in QL17 G-III stands for “Quick Load”, which means it’s quick to load a new roll of film. It’s almost as quick as with a later-day automated camera:
Put the roll in the camera and push down the rewind crank. Pull the film out to the orange mark and then start closing the back, making sure the film is on the white cogs before closing completely. The film is now ready to be advanced.

You can tell that the film is moving forward by the rewind crank turning and by the red/white stripes moving in the little window on the back.
There were a few other Canon cameras in the 1970’s with this feature, even SLRs like the Canon FT QL, but the QL17 G-III (and its sibling the QL19) were the last ones. The successful Canon AE-1 of the late ‘70’s isn’t very hard to load either, but it’s not as easy as with the QL17.
The Little Red Window
The QL17 G-III is fitted with a small window on the back where you can tell if the shutter is cocked and the film has been advanced. Red means it’s ready to shoot, white means it’s not.
In the words of the manual, where it’s known as the “Film Indicator”:
The film is wound up if the color of the film indicator turns red. The indicator turns white when the shutter is released.
The repair manual instead refers to it as the “Shutter Charge Index Window”.

I can’t recall using this feature. If unsure I just check by trying to pull the advance lever, but if you don’t want to advance the film until you’re going to shoot you might find the little window useful.
But still no sight of a QL17 G-III.
On Portra 400VC, probably at f/16
Small World
Last night, on a software developer event in Stockholm, I ran into a guy with a QL17 G-III. He said that he usually shoots medium format, which he seems to do well.
Film cameras are a very rare sight in Stockholm and I’ve never seen anyone else with a Canonet. I realize now that I should’ve taken a “Tokyo Camera Style”-style photo of it.
Sometimes the Canonet doesn’t put enough spacing between the frames. This is apparently causing confusion at the photo lab.
Batteries: Adapters
The QL17 was made for mercury batteries, which had lots of good properties, but the drawback of being filled with poison. So for current users of the camera, what are the options?
6) Battery Adapters
With a voltage-converting adapter you can get correct metering with long-lived and cheap silver-oxide batteries. The drawback is the one-time expense of $33 + shipping, which feels steep if that’s what you spent for the camera itself.
The “MR-9” adapter from CRIS is one option (found at CRIS’s or here). It isn’t without its problems—its limited output prevents the QL17 G-III’s battery check light from lighting—but it’s supposed to work otherwise. (Unfortunately their international shipping charges are ridiculous).
Another option is this guy (PDF), who offers both do-it-yourself instructions or builds adapters for you at a low cost.
I haven’t tried any of these adapters yet.
Batteries: Silver-oxide
The QL17 was made for mercury batteries, which had lots of good properties, but the drawback of being filled with poison. So for current users of the camera, what are the options?
5) Silver-oxide batteries
A silver-oxide battery has a stable voltage, much like a mercury battery, but at 1.5V instead of mercury’s 1.35V. This means you’ll get incorrect exposure, but at least the error is the same through the battery’s lifetime, unlike with alkaline batteries.
The error is supposed to be around 1 to 2 stops, so with print film you may get away with it. Otherwise you’ll have to figure out how much the error is, by comparing with another camera or light meter, and then using the ISO (ASA) setting to dial in the adjustment needed.