Macro converters fit between the camera body and a standard 50 mm lens (in the same way as a tele converter), and provide a range of magnifications up to 1:1. In the same way as a tele converter, they increase the focal length of the prime lens, but they also provide additional and variable extension for increased magnification. Some provide a range from infinity to 1:1, others from 1:10 to 1:1. They are convenient to use and the results are good, although the image in the viewfinder can be rather dim. The doubling of the focal length causes a 2-stop light loss, and the extra extension and magnification cause up to another stop light loss. TTL metering will provide correct exposure, and the converter will probably be supplied with exposure factors for non-TTL use. Macro converters can be used with some lenses with a focal length greater than 50 mm, but cannot then provide 1:1 magnification.
Made only by independents, and only for 35 mm cameras. Brands include Panagor (1:10 to 1:1), Kenko (infinity to 1:1), TelePlus (infinity to 1:1) and Vivitar (infinity to 1:1).