Why is Gary's 500mm fixed-focus lens so cheap and easy to use?

First of all, to correct, the manufacturer of this domestic soil gun is Jia Rui, not Jia Rui.

The reason why this telephoto lens is cheap is, firstly, fixed focus, which reduces a lot of troubles, and secondly, catadioptric structure, which can greatly reduce the volume and weight of the lens. Finally, it has no autofocus. Coupled with the saving of processing technology and materials, it can be made cheaper.

Of course, the price paid is not small. The maximum aperture is 6.3, which is not bad in a reflective lens. Long focal length has no pain of autofocus. There is also a strange Jiao Wai effect. The Jiao Wai effect of ordinary lens pursues the melting of cream, and the concave lens has obvious defocus and the light spot is "double eyelid", which is called doughnut by the person you like.