I don't understand your question. The optical parts are in the lens. The lens, at least in most mirror cameras, whether using single or double-lens, small-, med

I don't understand your question. The optical parts are in the lens. The lens, at least in most mirror cameras, whether using single or double-lens, small-, medium-, or large-format, are detachable. Most popular legacy mounts such as M42 can be used on modern DSLR and mirrorless systems with an adapter. Some, such as Nikon F-mount, don't even need an adapter. There are millions of images floating around taken this way, with varying technical/artistic quality.