Your information that there is approximately 9 to 10 mm of flat glass between the lens and the G1 sensor is completely new to me. That would make the optical situation practically the same as in the Bolex H16 RX camera. Then of course a RX type lens is needed for the G1 camera.
Originally Posted by Vivek
It's surprising information, but I'll assume you or someone else has measured it. The old RX/C rule is still very applicable to the interests of this strand. Just the conclusions will be different based on the new information. 1987 RX/C Rule:
A C-mount lens works well on a RX camera or a RX-mount lens works well on a C camera, if and only if:
(1) the lens is slower than about f/2 or f/2.8, or stopped down this far;
AND (2) the lens has a deep set exit pupil, about 1½ inches or farther into its screw mount.
[Note the second clause in the rule is based on the 12.6mm image diagonal of 16mm. The exit pupil distance would need to be increased for a 21.6mm diagonal sensor.]
This is not really about C and RX mount lenses and cameras. It's about lenses designed to image directly onto the sensor versus those designed to image onto sensors covered by 9.5mm of BK7 glass, and about cameras with uncovered sensors and those with sensors covered by 9.5mm of BK7 glass. It is not terribly important that the thickness be exactly 9.5mm or the glass be exactly BK7. (The glasses you describe are generally like BK7.) The location of the 9.5mm pane, nearer or farther from the sensor, is immaterial.
The point remains that you can't have it both ways. If at full aperture the 26mm f/1.1 Macro-Switar RX lens works well on a camera (because the camera is effectively RX type) then at full aperture the popular and common 25mm f/0.95 Angenieux does not work well on that camera. Likewise the Zeiss, Canon, Kowa, Nikon and most all superfast normals don't work well at full aperture on that camera.