Canon M extension tubes

[mjs1973]

I have decided to add an extension tube or two to my AE-1 arsenal. I want to experiment with some macro shooting with Velvia film this summer, so I'm looking at extention tubes and an inexpensive way to get some close up. I have found a set of Canon M extension tubes, and even found a website with directions for useing them.

http://www.canonfd.com/

My question is, what do they mean my manual diaphram control?? Does this mean that I would not be able to use the A setting on my FD lenses? not that it matters to me, I set everyting manualy anyway. I'm just wondering if the Canon M tubes would work without having to by anything extra. I don't want to spend a ton of $ on them but I don't want to get something cheap and then have to find another piece of equipment to get them to work...

Thanks in advance.

[mjs1973]

OK, I did a little more research and I think I was able to answered my own question. With this type of extention tube, I would have to stop down the apperture manually, then take a meeter reading prior to taking the shot. There are no mechanics to this type of tube, as far as I can tell, so everything that the camera would tell the lens to do, I would have to do myself. If I'm wrong, please correct me.