After some research I ordered two $49 lenses from Sunex, the DSL 377 2.5mm f2.8 (14mm in 35mm format) and the DSL355 4.16 f2.8. (23mm in 35mm format) To make it fit the Q, I also ordered a s-mount to c-mount adapter to fit a Pentax Q C-mount adapter. Yes that’s two adapters needed. Unfortunately, the 2.5mm didn’t have enough interfocal distance and did not work on the Q. (Lens too far away from the sensor glass). Should work on the Gopro though.
The lenses are made for a notch smaller 1/2.5″ sensor and not 1/2.3″. That makes the lens covering about 9% less than needed. The result is some hard vignetting in the corner tips, but only when shooting full frame 3:2. Shooting in 16:9 mode on the Q pretty much eliminates it. Therefore, video shooting is unaffected, except when turning the stabilizer on.
The Sunex lens is a board lens intended for video cameras. You will get focus from maybe 2 meters to infinity without touching the lens. The barrell distortion is acceptable, but the image quality in large still images is a bit soft and there are some color distortion.
For video shooting, the lens is pretty decent. It provides enough details for the Pentax Q’s not so perfect video resolution at full HD video.
Here is a raw video test. Notice that the cross processing filter is on.
Full size images:
External test of the DSL 377 2.5mm: