Typically, a long focal length of 800 mm also has an overall length of nearly 80 cm to the sensor plane. To achieve a handy, versatile, and compact solution, this lens employs a clever trick. The light path is simply folded using two high-precision ground mirror rings. This results in a compact design of just 131 mm in length compared to the mentioned 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 settings, depending on the camera. In the folded light path, it is technically impossible to incorporate an iris diaphragm. If light reduction is necessary, this can be easily achieved with 2x or 4x neutral density filters, which are screwed in front of the rear lens. There is a thread M30x0.5 available for this purpose.

Practically: The lens does not have a fixed infinity stop. Fine focusing is performed by swinging the focus point from out of focus to sharp and back to out of focus at any distance.

T2 connection, operating tip: The T2 adapter is screwed onto the optics, and then the lens is locked in place. The side screws on the T2 adapter allow for adjustment after loosening, enabling the lens to be oriented with the index pointing upwards. Retightening the screws securely holds the optics and adapter in place.

Advantages of a full-frame lens on a camera with an APS-C sensor: Save time in post-processing. Many lens errors such as distortion, edge softness, or vignetting occur in the outer areas of the image. By using a lens designed for full-frame on a camera with an APS-C sensor, these areas are not utilized, thus achieving maximum quality.