JIMK
Alright, home now, with camera in hand. Gee, I haven't used the Canonet 28 in over ten years. I remember now, that when I did use it with a popper, I did it just as I now do with the Canon GIII QL-17. I put one of my small Vivitar poppers on it, set the flash unit to f/8 and the camera to f/8, and fire away. Perfect exposures every time. However, I did just notice an extra contact on the cameras hot shoe, so I did some checking, and found this bit of information on it.
"The Canon shutter is entirely stepless from 1/30 to 1/620 seconds. It's not TTL metering as the CdS cell is located right above the taking lens, but it still does a great job.Since the CdS cell is on the lens mount itself, a handy feature is that if you forget to leave the lens cap on (a common mistake with rangefinders as the viewscreen doesn't go black as with SLRs), the camera's slow-shutter interlock functions and you can't take a picture. Sweet.
Although the Canon Museum says this unit features parallax compensation, my one doesn't. It only has a spare set of gridlines in the viewfinder that one is supposed to use at close distances. The Canonlite flash that came with it can be coupled with the metering system through an extra pin on the hotshoe. This allows for full "plug-and-play" nighttime shots, that is if your Canolite wasn't DOA. Grr.
The program automatic exposure is annoying. There, I said it. In daylight, it gives you the shutterspeed reading, but the aperture it hass selected is a mystery (somewhat - it selects mid-apertures in most cases). When trying to flash sync, you can't take advantage of the Copal shutter's ability to sync at any speed. Moving the aperture dial off automatic exposure also locks down the shutter speed to 1/60 (I think)"
Personally, I think you're better off with a small, very cheap auto flash unit. In that way, you control the aperture, and you don't dump the whole flash load on every shot. When I use the Canon GIII QL-17 in this manner, I get consistently good results. If I remember correctly, the 40mm f/2.8 lens on the Canonet 28, is pretty good. The bummer is that it's totally auto exposure, when shooting in the "A" mode. No manual override. So the aperture settings are only good for flash shooting.
Russ