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adapter/c mount lenses


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#1 Lee Young

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Posted 24 March 2009 - 11:23 PM

has anyone ever used a lens mount adapter to use c mount lenses on an arri sr bayonet mount. I have found a place that sells them. The Arri SR my school owns comes with the 10-100 F3.1 Zeiss, but I need the speed of some prime lenses. I was just wondering what your experiences were and what your thoughts are on it. Did the adapter give you infinite focus? Where did you buy it, etc.
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#2 Ian Cooper

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Posted 25 March 2009 - 03:23 AM

has anyone ever used a lens mount adapter to use c mount lenses on an arri sr bayonet mount. I have found a place that sells them. The Arri SR my school owns comes with the 10-100 F3.1 Zeiss, but I need the speed of some prime lenses. I was just wondering what your experiences were and what your thoughts are on it. Did the adapter give you infinite focus? Where did you buy it, etc.



Are you sure it was to put a C-Mount lens on an Arri bayonet camera, and not to put an Arri bayonet lens on a C-Mount camera??

The reason for asking is that the flange focal distance for the Arri mount is 52mm, the distance for C-mount is 17.526mm. The adapter you're talking about would have to position the c-mount lens 34.474mm back inside the arri camera! This assumes that it is indeed possible without colliding with the shutter and other internals of the camera, or the outside diameter of the lens jamming against the front of the camera.

Adapters to put arri mount lenses on C-mount cameras are available and will work easily, as the adapter has to position the bayonet mount 34.474mm away from the original C-mount on the camera.

The general rule seems to be that lenses with a flange focal depth greater than the camera mount can be used with an adapter, but adapters aren't available for lenses with a flange focal depth which is less than the camera's.

Now, I'm aware there are exceptions to that 'rule': The Bolex bayonet mount has a FFD of 23.22mm yet you can get (from Bolex no less) adapters to use C-Mount lenses with it. This adapter is able to set the c-mount back the required 5.694mm because the distance isn't great and the diameter of the Bolex bayonet mount is quite large. I would also take a guess that as historically Bolex cameras had always used c-mount lenses, when the bayonet mount and cameras using it were designed, it was intentionally made backwardly compatible with the lenses their existing customers already had.
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#3 Lee Young

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Posted 25 March 2009 - 12:05 PM

Your concerns are in fact correct. I just got off the phone with the company that I supposed had one. The guy told me that it was the other way around. They did list it the other way though. I've noticed some inconsistency in how they list adapters. It's very confusing. Thank you for your comment though.
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#4 Ian Cooper

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Posted 25 March 2009 - 12:38 PM

No problem, as well to double check!

The short FFD of the C-Mount means that pretty much any other lens can be used on a C-Mount camera with a suitable adapter
...but it makes adapters to use C-Mount lenses on other cameras pretty rare!
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