Today I present a relatively little-to-find lens: the Sigma Mini Wide II 28mm f/2.8. I have no idea how old it is. You can also find on the internet very little information on this lens. On the other hand: you pay very little money for it. Usually it is yet to get for 15 to 25 euros.
Here is a comparison: the Sigma 28mm mini wide II at the minimum focusing distance in macro function 1:4.5. And below the OM Zuiko 50mm f/3.5 Macro with 1:2 reproduction ratio:
The lens is pretty sharp even at full aperture, but falls towards the edges slightly. Stopped down to f/5.6 or f/8.0, the lens is sharp as a razor from one edge to the other. Therefore more suitable for sunny days when you need proper sharp images.
The lens was made with a variety of bayonet sockets. One finds the Sigma Mini-Wide II for Canon FD, but also for Minolta or Olympus OM. It is getting very low in any case. And if you can or want not spend much money then the Sigma Mini Wide 28mm is always a good choice.
Here are some image results with this lens at maximum aperture: