On your 40D, a 180mm is a pretty long lens. Shooting close-ups and macro, it will require some significant working distance, probably a tripod most of the time since you will need to stop it down for adequate depth of field. Unless you want the compression of a longer telephoto lens and/or super thin depth of field effects, I'd suggest a shorter lens for use on your crop camera. The background blur shown above is a bit misleading... By itself, the background blur isn't a reason to choose the longer lens (note, too, that Kawi_200 is shooting with full frame camera). All you have to do to get greater blur with the shorter lenses is open up the 100mm to f8 or so, and the 60mm to f5.6 or f4, to get similar blur effects.
I've had the Canon 180/3.5L for many years and, frankly, used it little when I was only shooting with crop DSLRs. Occasionally if shooting anything that stings or bites or is poisonous, perhaps. But mostly I only use it on film/full frame. It's just a pretty darned long lens on a crop camera. 150mm and up macro lenses are fairly specialized, often not as fast focusing and less dual purpose.
The 24-70L can do close to 1:4 or one quarter life size, all on it's own. Call it close-up, if not macro. You could just add an extension tube or two to that lens (the Kenko sets are good) to be able to focus a lot closer and get higher magnification. It holds up well and gives nice quality shots with extension rings.
If you prefer a true macro lens, which will be easier in some respects than working with extension tubes, I'd recommend something in the 60mm to 105mm range. Those are the easiest to handhold for relatively casual macro shooting, and yet can be used for full 1:1 if needed (can even be used for higher magnification if needed, by adding extension tubes).
The suggested range still offers a lot of possible choices:
Canon EF-S 60/2.8 (fairly compact, USM, crop only)
Tamron 60mm f2.0 (unusually fast aperture so it should double well as a portrait lens, nice price, relatively compact, crop only)
Sigma 70/2.8
Tamron 90,2.8
Tokina 100/2.8
Canon 100/2.8 USM
Canon 100/2.8L IS
Sigma 105/2.8
Sigma 105/2.8 OS
The two Canon lenses have a few advantages:
- They both are USM, so can double nicely for non-macro uses (some Sigma are similar HSM, some Tamron are similar USD).
- They both have focus limiter switches, which also helps them focus faster for non-macro work, making them more dual purpose.
- They both can be fitted with a tripod mounting ring (sold separately... Canon's is expensive, but there are cheaper clones on eBay and elsewhere that seem fine). This is a handy thing to have!
- They are IF or Internal Focus lenses..... This makes them bigger, but they don't grow in length when focused really close. Many macro lenses have a huge amount of extension when focused to 1:1. This cuts into your working distance.
- The 100L has IS.... I don't know that it's all that useful for macro shooting, but it might be handy for non-macro work. (Note, at least one Sigma now has OS, their version of IS.)
As to image quality... You really can't go very far wrong with any of the above. Check out specific lenses you might be considering on the Lens Sample Photo Archive sub-forum attached to this forum. You can find examples made with practically any lens there.
You can get some idea how 60mm or 70mm lens would "feel", from your 24-70... even if it's not all that "macro" by itself.
