Canon 500D Close-Up Lens: Questions (also: Alternatives?)

Hi all,


I had started a thread some time ago asking opinions between choosing extension tubes and a close-up lens (see here).


I have a few some follow-up questions on the 500D (the close-up lens, not the camera!):


- Are there any disadvantages to using it with a step-up ring? (I'm probably going to get the 77mm one to use on my 24-105, but I would also like to be able to use it on my 70-200 f4 IS that has a 67mm thread)?


- Would it make sense to use it on my 70-200 in conjunction with the 1.4x extender (would that increase magnification at all)?


- Are there any (good quality!) alternatives to the 500D in 77mm filter size? I somehow doubt it, given that Nikonians also seem to use the 500D, so it's considered very good. But, I thought I'd ask.


Thank you very much in advance for all your help!


Tony

There is also a Canon 250D, which is the same idea, but magnifies a different amount. The only other high quality close-up filter/lens I know of is the Sony M3358, which only comes in 58mm thread size, as far as I know.


This pageabout my old Sony camera, talks about the using Canon close-ups (500D, 250D), the Sony one (M3358), using a step-down ring, and stacking them for even more magnification.