Hi Bobbo,
I happen to have both a Canonet Hood 4 and a Canonet Hood 5. I've read that the 4 is the proper hood for the Canonet QL17 GIII however the 5 works fine too. They both have a little cutout to see through when you look through the viewfinder so they don't block your view when framing a shot. Pictures shown below of each (Hood 4 on the left and Hood 5 on the right, as is evident from the printing on the boxes)
The only difference between the 4 and 5 that I have noticed is that the 4 is a round hood and the 5 has flats on opposing sides of the round hood. They both clamp on to the outside of the lens body with a thumb screw. And a neat feature is that you can reverse them so rather than sticking out they cover the lens body. Neat, not to protect the lens, but makes for a smaller package for traveling or putting in your pocket or bag.
Be forewarned, however, that the Canonet hoods are kinda pricey. Presumably because they're somewhat rare. I've seen them regularly sell for something like $45. Of course, you can always look for a generic 48mm hood which will likely be cheaper. But since I'm not really shooting with my Canonet these days I would be happy to sell you one of mine.
Best,
Randy
