The C33 is the camera Diane Arbus used in her mid-final phase of her photography. There are later, more highly engineered Mamiya twin-lens cameras but that 1960's model is totemic because she used it. She'd switched from cool 35mm Nikons despite the big uptick in hassle to get the greater resolving power from the much bigger 2 1/4 inch square negatives. As well as a move from rectangle to square format there's a completely different shooting style - looking down into the viewfinder (with the image laterally flipped on the focus screen), with kit that is perhaps best suited to the more sedate studio setting. Her set-up consisted of an additional rather clunky looking lens-hood (for better contrast, less flare, in side-lit conditions) and the powerful flash, which I think was sometimes strapped on the side. I presume she carried a light-meter but I saw her camera in a vitrine at a retrospective at the V&A and I seem to recall it had a piece of card on the back noting a couple of aperture/shutter speed combinations.
She was considering switching to a beefy (super expensive) Pentax 6x7 (SLR style) camera near the very end, useable like the Nikons but with medium format quality.
Just checked and the C33's sometimes come up on eBay and go for not that much.
I think this was taken by Tod Papageorge, in Central Park.