to match the very popular Minolta SR-T 101 SLR introduced in 1966
1st generation (1966-72)
coating quality not as good as later models but did use Double Coating Achromatic
often used radioactive elements which cause yellow discoloration of the glass as it decays - eg. the 58mm f/1.2 and the 85mm f/1.7
2nd generation (1972-76)
rubber focus ring instead of milled metal ring
black painted aperture ring instead of white metal ring
improved coatings
3rd generation (1975-77)
discontinuation of the two letter code on the front of the lens which indicated number of glass elements and groups
further improved coatings
MD (Minimum Diaphragm tab):
the addition of a new tab at the rear of the lens diaphragm ring, designed to connect with the XD series bodies minimum aperture switch, telling the camera that the aperture selected was the minimum aperture to allow shutter priority mode
1st generation (1977-79)
excellent quality and coatings
many were redesigned to be smaller and lighter to compete with the recently introduced Olympus OM system
most have 55mm filter threads
2nd generation (1979-82)
often the metal aperture ring was replaced with plastic
new lenses with slower apertures eg. 85mm f/2 instead of the older f/1.7 model
3rd generation to match the Program Mode of the X-700 camera (1981-)
placement of the MD aperture lock
further reduced size and weight
many were of cheaper build quality to compete with increasing competition from third party lenses
clip on lens hoods instead of screw on
the last of these to be introduced was the 100-300mm f/5.6-6.7 zoom in 1996