Normally, a long focal length of 800mm also has a total length of almost 80cm to the sensor plane. In order to achieve 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 a compact design of only 131mm in length - compared to the almost 80cm mentioned above. The close focusing distance is also reduced to 3.5 metres - instead of at least 10m with a lens objective. Focussing is manual. The lens can be used (depending on the camera) with aperture priority or manual exposure setting. It is not technically possible to use an iris diaphragm in the folded beam path. If light reduction is necessary, this can be achieved simply by using 2x or 4x grey filters. These are screwed in front of the rear lens. An M30.5x0.5 thread is provided for this purpose. Practical: The lens does not have a fixed infinity stop. Focusing is carried out "oscillating" by reliably finding the focal point from out of focus to in focus to out of focus at any distance. T2 connection, operating tip: The T2 adapter is screwed onto the lens, then the lens is locked on. After loosening the screws on the side of the T2 adapter, the lens can be "raised" - the index can be aligned upwards. Tightening the screws again reliably secures the lens and adapter. A large number of lens faults such as distortion, edge blurring or vignetting occur on the outer areas of the image. If a lens designed for full-frame format is used on a camera with an APS-C sensor, these areas are not utilised. This ensures maximum quality. Additional post-processing time to correct lens errors is therefore not required. T2 connection: available adapters: Canon EOS, Canon FD, Nikon AF/MF, Olympus OM, Olympus 4/3, Olympus micro 4/3, Minolta AF, Minolta MD, Pentax, Leica R/SL, Praktica M42, Samsung, Sony Alpha Tip: doubling the focal length with optional walimex 2x converter art. no. 12602, results in a 16/1600mm or a 16/2400mm With this article number, the T2 adapter is not included in the scope of delivery. Please also order or order the lens as a unit with T2 adapter for your camera