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Thread: Stupid question

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    Senior Member fordfanjpn's Avatar
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    Stupid question

    I have to admit to being totally ignorant of optical theory, so it's possible that this is a really dumb question. But here it is. I recently bought a cheap Canon FD adapter for 4/3 from a Chinese company on ebay. The ad clearly stated that it would not allow the lens to focus at infinity, so I didn't have great expectations. What happens when I mount my 50mm FD lens on the G1 is that I end up with a really good 50mm macro lens that won't focus beyond a foot or so. I'm not complaining because the lens only cost about $30, and it really does make a wonderful close-up lens. But I was wondering why this happens, and why an adapter from RayQual, for example, doesn't have this problem. I'm thinking about getting the RayQual adapter too, but I am curious as to the mechanics behind all this voodoo and witchcraft. Can anyone explain it in such a way that even I can understand?

    Bill

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    Re: Stupid question

    Bill, the Rayqual FD adapter works because it puts the lens at the proper distance from the G1 sensor.

    With the FD 4/3 adapter and the Pana 4/3 adapter on the G1, the lens is farther away from the sensor, so it's like having an extension tube, hence it only focuses close up.

    more here: http://en.wikipedia.org/wiki/Flange_focal_depth
    Last edited by monza; 28th January 2009 at 21:59.

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    Re: Stupid question

    Quote Originally Posted by monza View Post
    Bill, the Rayqual FD adapter works because it puts the lens at the proper distance from the G1 sensor.

    With the FD 4/3 adapter and the Pana 4/3 adapter on the G1, the lens is farther away from the sensor, so it's like having an extension tube, hence it only focuses close up.

    more here: http://en.wikipedia.org/wiki/Flange_focal_depth
    That certainly makes sense. But I also bought a cheap Nikon adpater, and it works fine, even on top of the 4/3 to M4/3 adapter. I guess it all comes down to that distance between the lens and the sensor. Thanks for the reply.

    Bill

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    Re: Stupid question

    Yep, the Nikon flange distance is 46.50mm, the Canon FD is 42.00mm, the 4/3 is 38.67. It's tough to make an adapter than is only 42 - 38.67 = 3.33mm thick...just not enough room to work with, when some of that space has to be for bayonets, etc.

    The Nikon has nearly 8mm to work with when compared to 4/3.

    http://www.graphics.cornell.edu/~wes...-register.html

    Doing a direct FD --> 4/3 is much easier: roughly 22mm difference.

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    Re: Stupid question

    Yes, as Robert explained, it is the tiny distance that makes the m4/3rds to M adapter very tricky to fabricate (hence more expensive) besides all the lens/camera release mechanisms and all that.

    It is tricky even for a well known manufacturer like Novoflex to get it right.

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    Re: Stupid question

    Thanks for all the info guys. I appreciate your taking the time to reply. I feel smarter now!

    Bill

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    Re: Stupid question

    Quote Originally Posted by monza View Post
    Yep, the Nikon flange distance is 46.50mm, the Canon FD is 42.00mm, the 4/3 is 38.67. It's tough to make an adapter than is only 42 - 38.67 = 3.33mm thick...just not enough room to work with, when some of that space has to be for bayonets, etc.

    The Nikon has nearly 8mm to work with when compared to 4/3.

    http://www.graphics.cornell.edu/~wes...-register.html

    Doing a direct FD --> 4/3 is much easier: roughly 22mm difference.
    Note the issue is as much the breechlock as the thickness difference. It's much easier to do a working adaptor for bayonet lenses. There's any number of EF mount adaptors with thicknesses in the 1-2mm range (Contax and Pentax K adaptors most notably)

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