MysteryOnion: +1 on the dimensions for the Pentax-110 body and lenses
I made a sketch of them for my own use and put them here in case anyone as crazy as me wants to make a Pentax-110 to M43 adaptor:
https://www.box.com/s/b9319930073aad14e911
Then I moved the waterhouse stop to the correct position -actually about 0.1 mm to the sensor side of MysteryOnion's measurement, the first one I made is not quite right. The stop is machined of brass with a 4.5 mm hole for f/4 on the Pentax-110 18 mm lens, and has a blade thickness of about 0.2 mm and is coated with Krylon UltraFlat.
It made a big difference to the edge sharpness
Here is an image without the stop, which is also similar to having the stop in the incorrect position:
https://www.box.com/s/19814d0770789469cba8
With the f/4 waterhouse stop in almost the correct position in the adaptor:
https://www.box.com/s/f7b4205014069b6b453a
There is still some blur out in the corners but the stop made a big improvement.
Actually with these small M43 sensors having un-natural wide DOF, "I feel" a bit of corner softness is more natural.