Normally, a long focal length of 800 mm also has an overall length of nearly 80 cm to the sensor plane. To achieve a handy, universally applicable, and compact solution, this lens employs a clever trick. The light path is simply folded using two high-precision ground ring mirrors. This results in a compact design of only 131 mm in length compared to the aforementioned nearly 80 cm. The minimum focusing distance is also reduced to 3.5 meters instead of at least 10 m with a lens-based system. Focusing is done manually. The lens can be used with either automatic exposure or manual exposure settings, depending on the camera. It is technically not possible to incorporate an iris diaphragm in the folded light path. If light reduction is necessary, this is simply achieved using 2x or 4x neutral density filters, which are screwed onto the rear lens. There is a thread M30x0.5 available for this purpose. Practically, the lens does not have a fixed defined infinity stop. Focusing is done by swinging, allowing the sharp point to be reliably found from out of focus to sharp and back at any distance.