I love seeing weird and quirky lenses and this one from Samyang certainly ticks those boxes. Is it any good though?
The Samyang 300mm f/6.3 ED UMC CS is a mirror lens for APS-C mirrorless Canon or Sony cameras. I've never used one personally, though many mirror lenses do exist and their correct name is "catadioptric" lenses. I'm going to just directly quote a Wikipedia page for a summary:
A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses (dioptrics) and curved mirrors (catoptrics). Catadioptric combinations are used in focusing systems such as searchlights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses. Other optical systems that use lenses and mirrors are also referred to as "catadioptric", such as surveillance catadioptric sensors.
In a practical sense for photographers, what this does is allow a much further reach via a longer focal length without the substantial increase in the size and weight of the lens. The method does come with some drawbacks, some of which Frost points out in the video. It also, in this case at least, comes with some bizarre quirks too. For example, the lens appears to be sharper (possibly through the clearly increased contrast) at the corners of the image and softer in the middle; the opposite of almost every lens on the market. The results are also pretty underwhelming across the board but it's a reasonably inexpensive acquisition, has interesting bokeh, and isn't a bad talking point with other 'togs, if they're bored.
Have you used a catadioptric lens? Would you recommend them?