Normally, a long focal length of 800mm also has a total length of almost 80cm to the sensor plane.

In order to obtain a handy, universally applicable and compact solution, a trick was used for this lens. The beam path is simply "folded" by means of two high-precision ground ring mirrors, resulting in this compact design of only 131mm in length - compared to the almost 80cm mentioned. The closest focusing distance is also reduced to 3.5 meters instead of at least 10 meters with a lens.

Focusing is manual. The lens can be used with aperture priority or manual exposure (depending on the camera).

It is technically not possible to insert an iris diaphragm into the folded beam path. If light reduction becomes necessary, this is simply made possible by gray filters 2x or 4x. These are screwed in front of the rear lens. There is an M30x0.5 thread for this purpose.

Practical: The lens has no fixed infinity stop. Focusing is performed in an "oscillating" manner, in that the focus point is reliably found from unsharp to sharp to unsharp at any distance.

T2 mount, operating tip: The T2 adapter is screwed onto the optics, then the lens is locked in place. After loosening, the side screws on the T2 adapter allow the lens to be "straightened" - the index is aligned to the top. Tightening the screws again reliably secures the optics and adapter.

Advantages of a full-frame lens on a camera with APS-C sensor
Save time in post-processing. A lot of lens aberrations like distortion, edge blur or vignetting occur at the outer areas of the image. If you use a lens calculated for full format on a camera with APS-C sensor, these areas are not used. Thus, the maximum quality is obtained. Additional post-processing time to correct lens errors is therefore not necessary.