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Canon FD to EOS adapter + crop factor and focusing?


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#1 luke grandmont

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Posted 06 February 2010 - 12:32 PM

Looking at picking up a fairly inexpensive, gently used long lens (400mm) for my 7D. It's an FD mount though. I've perused ebay for an adapter (FD to EOS) and there are a few options. Some without glass that seem to be only for Macro shots (infinity focusing is somehow disabled) and others WITH glass, though more expensive but described as being able to focus either way. Basically just wondering if anyone could explain the logic behind this, not that I'm questioning it, I just don't understand. Also, would anyone know the crop factor for an FD mount/lens?
cheers
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#2 Satsuki Murashige

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Posted 07 February 2010 - 12:02 PM

It's because the FD mount flange focal distance is shorter than for the EF mount, and it is not possible to put the FD mount inside the body cavity of the camera without surgically removing the EF mount - it has to go outside, which puts it too far away from the focal plane. So without the additional optics in the adapter to refocus the image onto the focal plane, the lens would not focus to infinity.

There won't be a crop factor, you should have the same field-of-view.
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