If you're considering the EF 180mm f/3.5L Macro USM, you have the budget for the EF 100mm f/2.8<span style="color: red;"]L Macro IS USM - and you should get the 100mm Macro with IS. A main advantage of the 180mm lens is a longer working distance, which is useful for small critters that are spooked by big lenses shoved toward their compound eyes - that's something that the hands of marital couples don't have a problem with, nor do inanimate rings. Also, you'll likely be doing those shots handheld, and the IS will be a definite asset for that.