Although instant-film cameras have been making a bit of a comeback, they still tend to be simple point-and-shoots, like the original Polaroids. The SL42 is different, though, in that it's an SLR (single-lens reflex) that uses interchangeable lenses and offers full manual control.
Created by Hong Kong-based startup NONS, the SL42 takes its name from the fact that it's compatible with existing M42-mount lenses. These are still being made, plus used models are widely available through sites such as eBay.
Instead of traditional 35mm film, however, the camera uses Fujifilm Instax mini film. Individual 46 by 62-mm (1.8 by 2.4-in) prints are ejected through a slot in the side of the camera body, once a dedicated button is pressed after each exposure.
The third-party lenses will already provide users with manual control of aperture and focus. Additionally, though, a physical dial on the camera itself lets them choose between 11 shutter speeds. There's also a hot shoe on top, for mounting a flash.
It should be noted that because M42 lenses are designed for use with 35mm film (and not the differently-sized Instax) the resulting photographs have a very marked vignetting effect – they're essentially round photos on a rectangular print. Depending on the user, this might or might not be a desirable quality.
Should you be interested in picking one up, the SL42 is currently the subject of a Kickstarter campaign. A pledge of HK$1,550 (about US$199) will get you one, without any lenses, if everything works out.
Source: Kickstarter