Reversing two old manual lenses.
I lately picked up a 50mm and a 28mm old manual lenses for about $10 each and tried them reversed to see the difference in resolutions. I also compared them to a Sigma 105 with and without a Raynox 250.
These are full size images (no cropping) reduced for posting.
Not bad cheap macro shooting IMO!
The advantage of the Sigma is the greater distance from the subject you can shoot from of course.