is compatible with all other K-mount cameras and lenses when in manual or aperture-priority exposure modes, however the extra pin needs to be removed for safe use on autofocus Pentax cameras, as it can otherwise become locked within the autofocus shaft. Lenses locked to the camera body this way are difficult to remove and may require complete dismantling. Adaptors to use on K-mount L39 / LTM Adaptors can be found to allow use of lenses with Leica M39 thread (screw) mount. If a lens originally intended for Leica Rangefinder cameras is used, focusing is limited to about 10 cm. However, some SLR lenses were made in LTM 39 mount, mostly by KMZ for use in the early Zenit SLRs which had LT 39 mounts. These "Zenit" TM 39 lenses will focus properly. Or these lenses can be used in conjunction with the M42 to LTM 39 adapter. M39 Adaptors can be found to allow use of a non-Leica 39 mm mount into the K-mount, typically as a M39-M42 adapter ring that is mounted in a M42-PK adapter; they may focus to infinity. M42 Pentax supplies adapters to fit M42 screw-mount lenses, as do several third-party manufacturers. The M42 screw-mount system was used by Pentax prior to the introduction of the K-mount. Pentax designed the K-mount wide enough to allow an adapter to fit between the M42 thread and the K bayonet. They also kept the same flange focal distance (also called registration distance or register) as the M42 screw-mount, so that M42 lenses focus correctly using the correct adapter (such as Pentax original or Bower). There are however other third-party adapters that add to the flange focal distance so that one loses the ability to focus to infinity. The loss of infinity-focus may not be significant in macro or close-up photography. There is great debate in the Pentax community over the applicability and safety of adapters other than those supplied by Pentax. Many users of third-party infinity-focus adapters, such as Bowers, report difficulty in removing the adapters from camera bodies. Such adapters may require modification before they may be safely used. Official Pentax adapters, and flanged non-infinity-focus adapters, do not provoke such problems. Many old M42 lenses have a modern-day cult reputation, including the (Pentax) Asahi Takumar range. Some manufacturers, including Carl Zeiss AG, still make lenses in the M42-mount. K-mount cameras have a suitable flange focal distance (45.46 mm)