Minolta introduced the RF Rokkor-X 250mm f/5.6 mirror lens in 1979 for its manual-focus SR-bayonet SLR system, alongside the longer 500mm f/8 in its catadioptric lineup. Lenses sold in North America carried the "Rokkor-X" name over a trademark dispute, while the same optical design sold elsewhere simply as "RF Rokkor".
It is a catadioptric design with 6 elements in 5 groups, a fixed f/5.6 aperture with no adjustable diaphragm, and weighs approximately 250g. A 39mm rear filter drawer accepts screw-in ND or clear filters for exposure control, the front carries a 62mm accessory thread, and minimum focus distance is 2.5m.
Because the aperture cannot be stopped down, exposure is controlled entirely through shutter speed or the rear drop-in filters, and out-of-focus highlights render as ring or doughnut shapes from the central mirror obstruction. Its main appeal is bulk: no conventional 250mm telephoto from the period is this compact.
These mirror lenses are popular for adapting to mirrorless cameras since they are fully manual, and clean examples with intact rear filters still trade steadily secondhand. Check the internal mirror coatings for haze or fungus by looking through the lens toward a light, and confirm the rear filter drawer is present.