The Pentax K-S2 should work with the Pentax-M 85mm. Here is a photo on flickr with this camera/lens combination.

https://www.flickr.com/photos/igor_di_k/17254115971/in/photolist-shFRy8-rkVW...-wncfw6-wEbjiX

Regardless of the details about how to get the best from an M lens, if you have the camera set to manual focus, it should take a photo whether it is in focus or not etc.

Severalsnakes, are you sure the whirring is the shake reduction? My K5 is silent when I half press the shutter (if using manual focus).

---------- Post added 11th Sep 2015 at 02:07 AM ----------

CORRECTION:

Sorry - Sevveralsnakes was right, and I was wrong (about the compatability).

This is the key point:
First, if your camera won't fire, set "Allow aperture setting other than A" to 2 (allowed) in the custom function menu.

I guess I changed this in the menu on my camera so long ago that I forgot I had, and forgot you had to. That should solve the problem.

Still not sure about the whirring though.

---------- Post added 11th Sep 2015 at 02:35 AM ----------

Britta, have you tried turning the shake reduction off? If that is the noise, then presumably if you turn it off, it shouldn't make a noise. If it does still whir, presumably it is something else.

Anyone else have a K-S2?

Last edited by rob_k20d; 09-10-2015 at 06:25 PM.

Still not sure about the whirring though.

---------- Post added 11th Sep 2015 at 02:35 AM ----------

Britta, have you tried turning the shake reduction off? If that is the noise, then presumably if you turn it off, it shouldn't make a noise. If it does still whir, presumably it is something else.

Anyone else have a K-S2?