I am also playing with the thought of going more into macro. Only thing is, my system is a Canon 20D, but the research that I have made recently may prove helpful for someone in here.
My setup is much like Roy's. I am using an old Vivitar flash bracket that I had since the mid 80s with a small micro ball head that I bought off of a local garage sale of all places. On the flash is a LumiQuest softbox. The lens is the Canon 100-300mm with a set of 3 automatic Kenko tubes. As you can see, the principals are the same as Roy's.
It would seem that I may need a better lens, one that is dedicated macro as I can only seem to get so close.
This is what I have found.
1. Canon lenses are super expansive in Canada. A Canon 100mm macro goes for 799, the same price as the Sigma 150mm macro. You do not get a lens hood (meh), but more importantly no tripod mount. The 180mm L is out of this world price wise. The Tamrons are also more expensive then the Sigma lenses. I find it interesting how different countries have different price points for different gear.
2. Tamron, Sigma, and Canon make 180mm macro lenses. The Tamron does not have a focus limiter, but then, most macro work is done manual anyhow. It also has a weird filter effect tool on the end of the lens that would affect dedicated macro flash setups during use. The Sigma is better built, but from online accounts, may or may not be slightly less sharp then Tamron and Canon. Some people say the Sigma is just as good as the Canon. Who knows. The Canon is a nice piece of glass, but way out of my price range currently. I just cannot see myself spending that much on a piece of glass for a hobby.
3. Sigma makes a nice 150mm macro that seems to be getting great reviews online. It comes with lens hood and tripod mount. It is unique and oddly enough, goes for the same price as the Canon 100mm..go figure.
4. If your interested in shooting bugs and other shy critters, you will want the most working distance you can get. This would mean a 150mm or 180mm at least. If your looking at mostly flowers or stamps, etc..then any macro lens should do you. It is only when your wanting to take photos of moving wildlife would you need the greater working distance. Much like Buddah Jones, some people place teleconverters on their macros to extend that reach with good results. From what I know, extensive research in mating the right lens with the right teleconverter is needed, as not all combinations seem to work as well, or may not even work at all.
5. Ring flashes give flat lighting and are intended for the medical world (which is what they were designed for). I think I will be staying with the single flash with a diffuser as it gives more natural light, and I do not have to spend a fortune on a dedicated macro setup.
Here is a list of pricing just to give you some ideas. These are all in Canadian funds.
Sigma 50mm macro f2.8 419.99
Sigma 105mm macro f2.8 519.99
Sigma 150mm macro f2.8 799.99
Sigma 180mm macro f3.5 999.99
Tamron 90mm macro f2.8 529.99
Tamron 180mm macro f3.5 1449.99
Canon 50mm macro f2.8 399.99
Canon 100mm macro f2.8 799.99
Canon Mp-E65 1399.99
Canon 180mm L macro f3.5 1649.99
From this short list for my area, it looks like the sigma 150 and 180s are a deal compared to Tamron and of course Canon.
Now, here is the quandary. do I spend a little extra and get the Sigma 180mm or spend less and get the 150mm lens plus a 1.4x Sigma teleconverter. I have been going back and forth for at least a month on this aspect. I am thinking however; that a macro lens would be better then the 100-300 that I am currently using with extension tubes.
Here are a few photos I have taken recently with the above set up. My goal is to get closer. I have a lot to still learn. These were all taken hand held.