C-Mount Navitar lens with Reflex Bolex - how can I adapt?

[Leanna Kaiser]

Hello all,

I have a reflex Bolex and recently got a C-Mount Navitar lens. I know they do not work with Reflex Bolexes out the box but I am wondering if anyone knows if there is a way to adapt it so there is enough space between the lens and the prism for use. (Perhaps some sort of 3D printed spacer?) Any ideas?

Thanks!

[Dom Jaeger]

Any regular C mount lens will work on a reflex Bolex, the issue is just that wider focal lengths (50 mm and under) can be optically affected by the reflex prism and the image will have some aberrations, making things a bit soft and bloomy.

Generally, the aberrations are reduced if you stop down to f/3.5 and beyond.

The only other thing to watch out for is if the C mount thread is too long. If the threaded part (or the optics) protrude back more than about 4 mm it won’t screw in all the way on a reflex Bolex and might even damage the prism if you force it. If a lens doesn’t seat properly it will act like a macro lens and only focus very close. There is no real solution to this, you just need to avoid lenses with a long C mount thread. 

[Leanna Kaiser]

Thanks Dom. That is the issue (the lens being too tight when I turn the focus, since it is a 6mm the back optics are rounded and it is protruding and I think it is hitting the prism.) I saw another post on here a long time ago about someone frankensteining two adaptors together to make a sort of extension tube, and am wondering if that could address the issue, say if I 3D printed a short length, or if anyone had found one pre-made since then. 

[Simon Wyss]

That won’t work unless you shoot macro. The lens needs to be seated against the turret for Infinity in focus. You can screw that lens on a Paillard-Bolex H-16 M. There you have a long mounting thread but no reflex view system.

What is it you are finding fascinating about the particular Navitar? It’s a machine vision lens, isn’t it?

[Leanna Kaiser]

Thanks, Simon. If there were an adaptor and the lens wasn't sitting flush with the turret, would I be able to get any focus at all? 

I'm not particularly fascinated with it, I'm just a completely broke filmmaker. I shoot mostly 16mm but also have a Black Magic that I can use C-Mount lenses with, I am just trying to be able to use the same lenses for both, when possible, as I can't afford to buy more. 

[Simon Wyss]

No adapter can bring the lens closer to the film plane of a C-mount camera. Elgeet’s wide-angle lenses for film movie cameras all have compatible thread lengths. This post-Elgeet Navitar simply isn’t made for your Paillard-Bolex H-16 REX-3.

If I can give advice, invest the little money you have in something more valuable for you, a tripod for example or an overhaul of the camera.

[Jon O'Brien]

Since you're broke can you sell that lens and some other stuff and maybe pick up a Nikkor F mount or an old but still okay Rx lens on Ebay? I use a Nikkor 50mm on a reflex Bolex with a low-cost C mount adapter. Sure, it's basically a telephoto lens but the images on the Bolex look beautiful. Or just stop it down. All the best with it and good luck. With filmmaking you just have to wait sometimes until everything comes together. But with patience it will. Shoot film!!

Edited November 11, 2023 by Jon O'Brien

[Leanna Kaiser]

Thanks! 

Edited November 11, 2023 by Leanna Kaiser