About that M42 adapter:
The M42 adapter that shipped with the camera is pretty clever. When attached to a screw-mount lens, the combination may be mounted the same as a K-mount lens with the interesting feature that the adapter is retained by the regular lens retention pin rather than the complicated system of small metal stops/springs used by Pentax. The flip side is that the mount itself lacks the usual adapter retention mechanism. Unfortunately, the special M42 adapter is hard to find, so hard to find that a good photo does not appear to exist on the Web.
Strong Caution!!
As noted above, while the lenses made for the Automat are broadly compatible to other K-mount cameras, the mount on the Automat itself is
NOT standard K-mount and may not play well with other than those Soviet lenses and accessories. The summary points regarding compatibility are:
- Standard non-flanged M42 adapters should not be used on the Automat. The mount lacks the standard stop/retention parts and the adapter may over-rotate in the mount and get stuck
- The cutout on the lower part of the mount face (used by the dedicated M42 adapter) has potential to foul or damage the contacts on KA and newer series lenses
- The retaining pin on the mount may not engage with some lenses due to slot designs that are less generous than those on Soviet/Russian K-mount lenses
The strong implication is that even a well-preserved and working Zenit Automat may not be a safe toy to use with one's normal "quiver" of K-mount lenses.
Again, the mount on the Automat is not a standard K-mount