C-Mount Lenses

Manufacturer Model Sensor Size Type Focal Length (mm) Aperture Filter Thread (mm) Blades
Canon V6x17 1” Varifocal 17-102 2.0 58 6
Fujinon CF8A 1” Fixed 8 1.8 52
Fujinon HF9A-2 23 Fixed 9 1.4 46
Fujinon CF12.5A 1” Fixed 12.5 1.4 52 8
Fujinon CF25B 1” Fixed 25 1.4 40.5
Fujinon HF35A 23 Fixed 35 1.7 49 6
Fujinon HF35A-2 23 Fixed 35 1.7 43
Fujinon CF50B 1” Fixed 50 1.4 49 10
Fujinon CF75A 1” Fixed 75 1.8 49 10
Computar H3616 12 Fixed 3.6 1.6 35.5 3
Opticom Fixed 8 1.3 40.5 6
Cosmicar H612A 12 Fixed 6 1.2 40.5 6
Cosmicar C815B 23 Fixed 8.5 1.5 40.5
Cosmicar B1214D-2 1” Fixed 12.5 1.4 40.5 6
Computar V5018 1” Fixed 50 1.8 43 3


The Pentax Q is the perfect camera for use with C mount lenses. With it’s flange focal distance of 9.2 mm, C-mount lenses with a flange focal distance of 17.526 can be easily adapted to the camera.

There are two adapters commonly available, an adapter consisting of a single machined piece of aluminum, and another that is constructed of two pieces of aluminum joined with set screws.

The one piece adapter:

The two piece adapter:

The one piece adapter seems to be more common, but it is the worse choice. It is almost 2 mm too thin, C-mount lenses used with this adapter will often need shims to be able to focus at infinity. The two piece adapter is much closer to the correct thickness, and most lenses will work without shims. The one piece adapter also doesn’t provide facilities for “clocking” the lens so that the focus and aperture markings are facing up, the two piece adapter makes this easy. Many C-mount lenses have set screws that can be loosened to allow the lens to rotate around the mounting threads, but it’s much more convenient to do it on the adapter.

Focus at Infinity

On forums I often see discussions about shimming C-mount lenses to achieve focus at infinity. On most lenses, adjusting the infinity focus is quite easy and removes the need for messing with shims. With many lenses, there are three small set screws near the front of the lens that can be slackened to detach the focus ring from the lens element. I will turn the ring to infinity focus, slacken the screws, then move the now-free ring to the middle of the focus range, then tighten one screw. Now I have a focus range that is shifted to half way past infinity. I find the infinity focus point, then loosen the one tight screw, reposition the ring so that the infinity stop is in contact with the stop on the lens body, and tighten three screws again.