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Canon FD lenses not focusing to infinity


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#1 Matthew K Thompson

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Posted 28 April 2013 - 05:29 PM

Hello,

I am wondering if anyone has experience using FD lenses on an SBM...with a bayonet to c-mount adapter then to a c-mount to FD adapter.  When I put some of my lenses on in this way, I can't focus to infinity (ie. distant objects are all out of focus..even when stopped down.)  Is this a problem caused by the use of two adapters?  I was told to do it this way by a reliable source, Andrew Alden, so I assume that it can work...maybe the lenses need to be adjusted???

 

any help is appreciated,

Matt


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#2 Dom Jaeger

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Posted 28 April 2013 - 10:28 PM

If you're not reaching infinity the lenses are sitting too far out from the film plane, and it sounds like in your case they are a fair way out, more than the little variation that you might expect from adapters. I've never tried that combination, but my guess would be that the C-mount to FD adapter is hitting something somewhere on the Bolex bayonet adapter before screwing all the way in. The C-mount seat is well inside the bayonet mount, so the FD adapter needs to clear the sloping sides of the Bolex adapter and the bayonet lock ring. You could check the adapter surfaces for signs of scraping where they join together, maybe a bit of filing will remove the obstruction.

 

Mr Alden may have used a differently shaped adapter that worked for him. 


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#3 Matthew K Thompson

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Posted 29 April 2013 - 10:26 AM

Thanks Dom!  You are right, the C to FD adapter is not screwing in as far as it should.  After looking more closely, it seems that it has a lip just below the threads on the "C-side" preventing it from reaching the end of the female threads on the C to bayonet... 

 

Much appreciated!


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