Minolta AF 500mm Reflex f/8

Put a stubby black cylinder the size of a large coffee mug next to a three-kilo refractive supertele and tell people both are 500mm lenses. They will not believe you until they look through them. This is the Minolta AF Reflex 500, the only autofocus mirror lens anyone ever put into mass production. Minolta built it from 1989, and when Sony took over the A-mount in 2006 they kept selling the same optical design unchanged, because nobody else had figured out how to autofocus a catadioptric lens and frankly nobody has since.

A mirror lens folds the light path back on itself with a primary and a secondary mirror, which is how you get 500mm of reach in a barrel under five inches long. The price of that trick shows up in the out-of-focus highlights. The secondary mirror blocks the center of the lens, so every specular point behind your subject renders as a bright ring with a hollow middle. Backlit water and bright twigs turn into a field of little doughnuts. Some photographers chase that look on purpose and others avoid the lens entirely because of it. Shoot a bird against bright branches and the background can get nervous and busy in a hurry.

Optically it earns more respect than its bargain price suggests. Center sharpness at f/8 is respectable for what you pay, while corners and edges stay soft, so it rewards keeping your subject near the middle of the frame. Because mirrors reflect light instead of bending it, the design throws off almost no chromatic aberration. No purple fringing on a heron's white feathers, which is more than you can say for a lot of cheap refractive teles. The trade is contrast. Mirror lenses scatter a little internally and veil easily when a bright sky sits in or near the frame, so files come off looking flat and want a contrast bump afterward.

The aperture is fixed at f/8 with no diaphragm at all, so you cannot stop down for depth of field or open up for light. At 500mm and f/8 the autofocus is slow and hunts badly in anything dimmer than open shade, and handholding without a fast shutter is a recipe for soft frames. This is a tripod-and-sunshine lens that people keep trying to use at dusk.

It survives as a cult budget supertele, the autofocus counterpart to the manual Tamron and Reflex-Nikkor 500 mirrors, and plenty of owners now run it on mirrorless bodies through an adapter. One metering habit pays off. Since f/8 never changes, lock Zone Light Meter to f/8 and let it solve for shutter and ISO, the only two things you actually control. Keep in mind that a mirror lens transmits a touch less than f/8 implies, so check the histogram and nudge exposure up if your frames keep coming back dark.