Slide copier
A slide copier is a simple optical device which can be fastened to the lens mount of a camera to enable slide duplicates to be made. Whilst these devices were formerly used to make duplicates on to slide film, they are often now used in conjunction with digital cameras to digitise images from film-based transparencies. This method usually gives better resolution than using attachments for digital A4 flat-bed scanners.
The devices are typically about 30 cm long, and screw into an intermediate 't-mount' attached to the camera. The lens in the copier does not need to be complex, because the systems are usually stopped down to small f numbers (e.g. for the Makinon Zoom Unit, f/16 at 1:1 magnification, falling to f/22 at 3:1 magnification), and the object and image distances are similar, so that many aberrations are minimised.
References
2. Makinon Zoom Slide Duplicator Data Sheet.