The Minolta Maxxum AF 500mm f/8 Relex lens was brought out in 1989, and is a Schmidt-Cassegrain catadioptric lens.
In 1672, Laurent Cassegrain designed a telescope using two mirrors to reflect incoming light to the eyepiece. This design corrected spherical aberrations and also made the telescope shorter. Later on the Catadioptric system was created, and his utilized both refraction and reflection … corrective lenses and mirrors. In 1930 Bernhard Schmidt redesigned the mirror shape and added an aspherical lens to correct for coma, and astigmatism aberrations. The Schmidt-Cassegrain design is currently one of the most popular telescope design used today … and it also caused many camera lens manufacturers to use that also. Almost everybody made one (well not really), but Minolta was the only one to incorporate it into their Auto Focus system.
The Maxxum 500mm reflex is a stubby barrel of a lens. Due to the way it is designed it can produce donut or crescent shaped bokeh … which probably explains why this lens is not more popular. As I mentioned before, this is an AF lens which can support centre point focus … and since this is a gear driven lens, the body has a direct influence on AF speed. You’ve got one aperture size of f8 so it can cause the AF to hunt … IQ is pretty good on this lens … you just have to know how to work the bokeh … overall I really like this small handful lens.