Ricoh is a Japanese multinational company founded in 1936. They produced 35mm film rangefinder and SLR cameras, in both M42 and Pentax K (bayonet) mounts. The company still produces digital cameras, as well as office equipment. However, Ricoh wasn't a big player, as far as M42 mount lenses are concerned.
They produced the 35mm film SLR Ricoh TLS Single, a camera that we like because of its excellent build quality and good ergonomics. There were at least two lenses that equipped this camera: the 55mm f2.8 auto Rikenon and the 55 f1.8 auto Rikenon.
The first one is just a standard, cheap 55mm lens that shows nothing remarkable and that has a far below average minimum focusing distance of 0.9m. The 55mm f1.8 feels and looks different and both are very well made, like most Japanese lenses that we've seen.
Check our Ricoh lenses:
The Rikenon Auto 55mm f1.8 is a faster standard lens made by Ricoh. It is faster and has a different exterior design than its 55mm f2.8 Rikenon sibling. It a well built lens which definitely has a say in terms of optical properties, with interesting color rendering and bokeh.
The 55mm Rikenon f1.8 has a minimum focusing distance of 0.5m, it weighs 208g and takes a 52mm filter. Number of blades: 6.
The Rikenon Auto 55mm f2.8 is a slower standard lens made by Ricoh. The build quality is very good, but the optics is not that great, as the minimum focusing distance of 0.9m is far below average for this focal length. It is rather light, weighing only 178g, and it takes a 52mm filter. Number of blades: 6.