Stupid question

[fordfanjpn]

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

 

[monza]

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

 

[fordfanjpn]

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

 

[monza]

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/~westin/misc/mounts-by-register.html

Doing a direct FD --> µ4/3 is much easier: roughly 22mm difference.

 

[Vivek]

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.

 

[fordfanjpn]

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

Bill

 

[mawz]

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/~westin/misc/mounts-by-register.html

Doing a direct FD --> µ4/3 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)