Walimex 500/6.3 DSLR mirror Pentax K

Typically, a long focal length of 500 mm is housed in a 500 mm long casing. To achieve a handy, versatile, and compact solution, a trick was applied in this lens. The light path is simply "folded" using two high-precision ground ring mirrors. This results in a compact design and an aperture that is more than 50% larger than that of a lens with the same focal length, as well as a very short minimum focusing distance of just 2 meters. Focusing is done manually. The lens can be used in aperture priority or manual exposure mode, depending on the camera. Technically, it is not possible to insert an aperture into the folded light path. If light reduction is necessary, this can be achieved with neutral density filters that screw onto the front of the lens. There is an M34x0.5 thread for this purpose.

The lens does not have a fixed infinity stop. Focusing is done "oscillating," securely finding the focus point from out of focus to sharp and back to out of focus. The T2 adapter is screwed onto the optics, after which the lens is locked in place. After loosening the side screws on the T2 adapter, the lens can be "aligned" so that the index can be oriented upwards. Retightening the screws reliably secures the lens and the adapter.

The advantages of a full-frame lens on a camera with an APS-C sensor include time savings in post-processing. Many lens errors such as distortion, edge softness, or vignetting occur in the outer areas of the image. Using a lens designed for full-frame on a camera with an APS-C sensor means that these areas are not utilized, resulting in maximum quality. Additional post-processing time to correct lens errors is therefore not required.