Hi
25mm/16mm: I guess you are referring to the diameter of the thread ?
You have tons of nice camera lenses that can be adapted to the Q bodies
D mount (thread diameter of approx 16mm)
This mount is mostly used for old 8mm / Super 8mm video cameras.
The mount is described here :
D mount - Wikipedia
Some nice lenses can be found, mostly for focals longer than 12mm.
Most of the wide angles produce vignetting, even on the small sensor of the Q, and even worse on Q7/QS1
The cheapest adapter I could find on Ebay can be found below
D mount 8mm movie lens to Pentax Q PQ P/Q Digital Camera Adapter Q7 Q10 Q-S1
C-mount (1 inch thread diameter):
This is a more recent mount used on 16mm vintage cameras/lenses and also for recent industrial vision lenses.
Obviously, the larger diameter with respect to D-mount allows less vignetting and better fitting to the Q7/QS1 line.
The mount is described here:
C mount - Wikipedia
The cheapest adapter on Ebay is here :
Lens Adapter For C Mount to Pentax Q Q-S1 Q10 Q7 | eBay
This adapter has the advantage of allowing to adjust the rotation of the lens around its axis, so the top writing of the lens can be effectively on the top.
Beware of the confusion between C and CS mount, that have the same diameter but different registration distances (CS have a shorter distance). No adapter exist for CS lenses on Pentax Q, except if you drill a 25mm thread into a D-mount adapter and add a suitable spacer, which requires a lathe.
So double check to buy real C-mount lenses for your QS1. CS lenses are mostly cheap plastic things that can be found on recent vision cameras. C lenses are generally more substantial, often with a metal body.
You can have a look at the (really) long thread "adapted-lenses-tested-q-reference-thread"
https://www.pentaxforums.com/forums/136-pentax-q/209474-adapted-lenses-tested...ce-thread.html
One of the very best C-mount lenses I can recommend to you are the cute Swiss Kern-Paillard lenses, particularly the 16mm, that are gorgeous. And also most of the Fujinon are pure marvels. Some Pentax/Cosmicar are also nice. The Kowa are also of very high optical quality.
Enjoy your time and welcome to the world of C-mount lenses for Q.