I am somewhat confused about the two Canon FD 2x teleconverters. I have seen reported that the 2x-A is recommended for lenses 300mm and longer and the 2x-B for lenses <300mm. I also have an old Canon brochure ("Canon Interchangeable Lenses" circa 1975) which describes the 2x-A as being appropriate for "any FD fixed focal length lens ranging from 100mm to 800mm or any FD zoom with 100mm in its range." This brochure does not show the 2x-B, so I assume it did not yet exist at that time. Why the discrepancy regarding the 2x-A? Did Canon change the optical formula for the 2x-A when the 2x-B was introduced? Any info would be much appreciated.

-- David Quanrud (dave@hwr.arizona.edu), March 10, 1999

Answers

The 2X-A was marketed much earlier than the 2X-B. I suppose that Canon realised that its optical formula was less appropriate for lenses with a focal length below 300 mm. Exceptions are the 200 mm f/4 Macro where Canon recommended using the 2X-A and the 300 mm f/2.8 L which apparently gives better results with the 2X-B. Both converters can also be used with zoom lenses. The 2X-A is recommended for zooms including the 300 mm focal length. There is also a 1.4X-A converter for fixed focal lengths of 300 mm and higher. According to Canon it is not recommended to use it on zooms.

Hope this helps.

Cheers, Hans

-- Hans H. Siegrist (hans.siegrist@fnis.ne.ch), March 11, 1999.

This is fine and the standard info. However I have a 2X-A that the instructions state that it should be used for lenses that are greater than 200mm in focal length, or zooms that have 200mm or greater at the long end of focal length.

And this is a 1980s version, well after the 2X-B was out.

-- Terry Carraway (TCarraway@compuserve.com), May 11, 1999.

Thanks to Hans for a thorough answer.

Terry--have you used the 2x-a with any 200mm FD lenses? How were the results?

-- David Quanrud (dave@hwr.arizona.edu), May 12, 1999.

David,

Sorry but I didn't get an email alert to your question.

I have used the 2X-A with a 70-210 f 4.0 Canon zoom with fine results.

I have a 200 f2.8 coming, so I can also try it with that.

Terry

-- Terry Carraway (TCarraway@compuserve.com), June 15, 1999.