Canon Macrophoto Coupler FL 55mm brand_Lightware The Mamiya RB67 is a

The Mamiya RB67 is a big

The base has a 3/8" inner thread for attachment to tripod or head

but this is still an unusual little lens

Leitz Canada Summilux 35mm f1

which doesn’t affect viewfinder function but will prevent other accessories from mounting to the top of the viewfinder

Canon Macrophoto Coupler FL 55mm brand_Lightware The Mamiya RB67 is aThe Canon Macrophoto Coupler FL 55mm is a lens reversing adjustable extension tube designed for macro use. You can use it directly on camera or on bellows its totally up to you. Attaches to FD FL cameras and lenses with 55mm filter threads. In excellent condition, with box. Lens, camera and bellows are sold separately.