Kowa 6mm F1.8 and Bolex S16

[Antoine Pret]

Hi, I got this Kowa 6mm lens that was originaly made for 1" CCTV. It appears that it peforms pretty well on MFT digital cameras so I was wondering if it would work on a S16 Bolex as it is C-Mount.

The lens covers S16 in the viewfinder but I can't seem to make it focus to infinity, I just get close focus. I think it is due to the back element being too close to the prism of the bolex.
 

So my idea would to either :

1. Add a c mount thread on top of the one existing, if such thing exist.

2.Remove the screws that retains the c mount and add a spacer to it.

Also, I measured the C- mount thread and it is close to 4mm when on my other lenses made for bolex it is 3mm, so there is also that.

Any help would be much appreciated, thanks !

[Dom Jaeger]

If you can’t reach infinity it’s because the lens is too far away from the film plane. So something is stopping the lens from seating all the way, possibly because the barrel is too wide for the adapter, or because the rear of the lens sticks out too much. Be very careful with C mounts like this that have deep rear protrusions (the rear optic protrudes well past the C mount thread), they can hit the prism. 

[Antoine Pret]

54 minutes ago, Dom Jaeger said:

If you can’t reach infinity it’s because the lens is too far away from the film plane. So something is stopping the lens from seating all the way, possibly because the barrel is too wide for the adapter, or because the rear of the lens sticks out too much. Be very careful with C mounts like this that have deep rear protrusions (the rear optic protrudes well past the C mount thread), they can hit the prism. 

So if I got this right, if i push back the mount toward the rear optic, it wouldn't work because the rear element would be even farest than before.

To be precise, the lens can't be screwed all the way in because it would hit the prism and with this I only get very very close focus (almost touching the lens).
 

So I guess I can't really do anything about it ?
 

Edited March 8, 2023 by Antoine Pret

[Dom Jaeger]

19 minutes ago, Antoine Pret said:

So I guess I can't really do anything about it ?

I’m afraid so.