I read that teleconverters don't work with macro lenses. Is that true, and if yes, why?
I have the Canon 100mm f/2.8L macro lens, and I felt that purchasing a 2x teleconverter would be a cheap way of getting a good 200mm lens.
Some suggest placing an extension tube between the teleconverter and the lens, but that is no good for my use, as I would loose the ability to focus to infinity.
Yes they work, I'm sometimes using one with my 100mm non-L macro with good results. However, there is a caveat: Canon and Sigma teleconverters do not work because they physically do not fit. There is a protruding bit at the front of the converter that fits into a corresponding cavity on the back of the lens - and only certain L Canon lenses have this. This means the various 70-200s and the longer tele primes, as far as I know. I don't know if the 100 L macro has this opening, from photos I've seen of it it does not look like it.
I am using a Kenko brand 1.4x teleconverter thas does not have this protrusion, which makes it fit just about any EF lens you'd care to mount it on. I put it on a 17-40L once, for laughs. They do make a 2x converter too. Basically the same products are sold under the Kenko, Tamron and Soligor brand names.
The canon 2x tc does not work with 100 2.8 macro. Its 1mm too long. You need an extension then the canon tc.
The 1.4 canon tc will fit
Yes, they work well. They allow you to double your magnification, or keep the same magnification but double your working distance.
You'll of course have less light transmitted and due to the magnification more camera shake. I can't think of any reason people would say they don't work with macro lenses. Possibly when focusing at infinity the quality might not be as good as a non-macro lens, being they are optimised for close focus, whereas normal lenses as a rule are optimised for infinity focus.
It depends on whether you are talking about a teleconverter that is put before the front lens (a "teleside converter") or between lens and lens mount (a "tele extender"). The latter essentially changes the magnification, and that will work in connection with what you put before it, at the cost of light yield.
Teleside converters don't usually have front threads. If they do, putting a closeup lens there will work fine but it will need to be of larger diameter of what you already have. Putting a closeup lens between the main lens and the teleside converter will not be of relevant help: the magnification of the teleside converter will be offset by a larger object distance you have to maintain, so you'll not reap any profit, particularly since teleside converters tend to minimise their lens errors for far distances rather than close distances.
