The 180L is an excellent lens...
I use it on full frame (film for the above) primarily. I find it pretty long on crop sensor cameras.
As you can see, depth of field can be incredibly shallow. That's one thing that makes the lens harder to use. To have any sort of DOF you have to stop down, and that in turn means slower shutter speeds. So most often I use it on a tripod or other support (for the above shot the camera and lens were on the ground).
The 180L is full featured:
- Internal focusing (IF) so it doesn't extend when focused closer. OTOH, this makes it a larger lens to start with.
- Tripod mounting ring is supplied (thankfully) and the lens hood is included.
- It has provision for mounting the Canon macro flashes, MT-24EX and MR-14EX.
- Focus limiter, which along with USM help it focus a little faster. But it's still nowhere near as quick focusing as a non-macro lens.
- It doesn't have IS, but I doubt it would be very much help at macro magnifications anyway.
I wouldn't say the 180L is the "best" macro... both Canon 100mm are also excellent. So is the more compact EF-S 60/2.8 for crop sensor camera users. The 65 MP-E is in a league of it's own. They're all different, I wouldn't call one better than the other. One of the 100s is probably the most versatile all around of the bunch, nice on both crop and FF, and they focus fast enough to be dual purpose, to use for non-macro work as well. The 180 is more "macro only". The 65mm is easily the most specialized of the bunch.
Do not get rid of your macro extension rings! They are very usable with macro lenses, too, and can come in handy for a lot of things.
Oh, and yes, the 300/4 IS is a pretty darned good near macro lens, too...
In fact, the 300/4L is the closest focusing of the Canon 300mm or longer primes. The above was slightly cropped from an image made near the lens' minimum focus distance. You could add some macro extension tubes to make it a bit closer focusing, but with 300mm focal length it takes a lot of extension to make very much difference.
I overlooked the 50/2.5 Compact Macro... just am not a big fan of shorter macro lenses. It's not USM and it only goes to 1:2 on it's own, uses a matched adapter to get to 1:1 that ends up all costing as much or more than some of the above lenses.
The Canon 45mm and 90mm TS-E lenses are also interesting to use for close-up work, too. Strictly manual focus, but that's okay with me since manual focus is usually easier for macro shooting anyway.
I haven't used the Sigma macros.... 105mm OS, 150mm OS and 180mm now also with OS. They also have offered 50/2.8 and 70/2.8... not sure if they still do. Can't really comment much... I prefer the Canon 100s over the 105mm, because it can't be fitted with a tripod ring (one is optional on the Canon). The 180mm OS is relatively new, I believe. Haven't heard too much about it. The 150mm OS has been around for a year or two and has some big fans.
Tamron has long made great macro lenses. Their SP 90/2.5 and 2.8 vintage, manual focus lenses are legendary and I still use a couple of them. One I've adapted for use on Canon...
The modern version of the 90mm with autofocus is very good and affordable. There's a new, less affordable version just coming available that's upgraded with their new USD focus (similar to Canon USM) and VC (similar to Canon IS and Sigma OS). Tamron's 60/2.0 is one of the fastest macro lenses available, but is crop only. (Zeiss offers a 100/2.0 Makro ZE for Canon, just be sitting down when you look up the price). I haven't used the modern Tamron 180mm.... The vintage 180/2.5 SP was a very nice lens, but not a macro.
Tokina also makes a couple really nice macro lenses. The 100mm AT-X is the latest in a long line of top quality macros. They also offer the shortest and most compact 35/2.8, but it's crop only.
Lots to choose among... there aren't any "bad" macro lenses. Most are optically excellent. Some are more full-featured than others... The Canon are among the most full-featured of them all.
