The Great Wall is a medium format SLR with a M39 mount lens and a shutter mounted in the body. This makes it perfect for experimenting with homemade lenses: you don’t lose the shutter when you take the lens off, and body caps to stick things to are cheap and readily available.
No other lenses were made for the Great Wall, but you can use Leica screw mount lenses (including old Soviet rangefinder lenses) which become extreme close-up lenses on the Great Wall because the flange-film distance is about double what it should be. Be sure to read about extension factors if you try this—with a 50mm lens on a Great Wall you need to add 2 stops to the exposure you thought you needed. Lenses shorter than 50mm won’t focus at all, they’re too far away from the film at any setting.
You can also use Leica screw mount extension tubes. The Great Wall lens only focusses down to 1m, but a short extension tube of around 7–8mm (I found a 7.25mm one) will convert the lens to focus from 50cm to 1m which is nice for faces. The extension factor is pretty small for this, maybe half a stop.
The Great Wall is a pretty awkward camera to use starting right from when you load it. Maybe spools are narrower in China, but the ones I have are incredibly difficult to get in. They work fine once they are in, but there’s a real knack to getting them there and no amount of twisting and forcing will substitute. Spend some time with an empty spool to figure out the angle before you try it with a film. I’m still not 100% on it; if I remember I load the film without unsealing it, and I only remove the tape when I have both the film and the empty spool loaded properly.
The viewfinder is pretty dim, even in the centre, and you’ll never know what’s in the corners of your pictures until they’re developed. It doesn’t have an automatic diaphragm either, so you need to remember to stop down before you take the picture—and once you’ve done this you won’t be able to see what you’re pointing at! It helps if there’s something bright in the middle of the image.
See that threaded hole next to the strap lug on the shutter release side? That’s a socket for a cable release. I didn’t figure that one out for five years! Not all cable releases fit it, though: the viewfinder hood blocks it, so you’ll need to find one with a slim collar.
You can spot Great Wall photos a mile off because there’s a step in the body that vignettes the top of the image. The lens has a signature too. It’s a 1930s design (a four element front-cell focusing Tessar clone) so while it’ll never be completely sharp it does get pretty good at the smaller apertures. The out of focus areas pick up a funky swirl when you open it up too. It’s only single coated so it flares a little, but I like that, it suits me. Don’t get me wrong, this isn’t a toy camera: the ways it puts itself into the picture are subtle, just there in the background. It’s a million miles from something like a Holga.
If you see one of these cameras then buy it, they’re becoming vanishingly rare.
Mine had a wobbly film advance knob, which eventually fell off. It’s held on with a screw in the centre of the knob, under the leatherette which I carefully peeled off with a scalpel. It seems the reason it was wobbly is that it had too many washers between the camera and the knob, so I took one of them out before putting it back together. This kind of thing is fairly common with Soviet cameras: they’d be made with whatever got delivered to the factory that month, so if they ended up with the wrong size washers then the cameras got made with the wrong sized washers. I guess China was much the same.