given the choice of buying either the Canon 100/2.8 Macro or the 180/3.5L Macro, which lens would you buy and why?
I have a 70-300 DO which with an extension tube can give me a magnification of 0.46x. as such, I'm having a hard time justifying buying the 180/3.5L with its large price tag. flying insects etc would probably fly before I could get close enough to photograph them with the 180/3.5L, but I'm not experienced with the Macro lenses so I could be wrong.
any experience and opinions would be helpful. there may be one or more points that I'm forgetting in my considerations of the two lenses.
The Tamron 180mm macro lens is highly regarded and in tests is at least the optical equal of the Canon. But it is nothing like as robust.
The 100mm and 180mm lenses are quite different beasts. Handheld flash photography is possible with the 100mm lens. It is possible but much harder with the 180mm lens due to increased focal length, size and weight. (I have tried, using Nikon equivalents.)
The 180mm has some significant advantages. The longer focal length means greater working distance for nervous subjects, and a narrower field of view making smooth out of focus backgrounds easier to achieve. It also has a tripod collar so that you can rotate the lens with ease (that is more useful than you might thing, especially when stalking a nervous insect).
But the 100mm lens is cheaper, lighter and smaller. And if you get up early in the morning, you can catch insects when they are inactive.
For general macro work the 100mm is better IMO. For dragonflies etc, go for the 180mm (Canon or Tamron).
Here's some tests:
Which would I buy? The Tamron 180mm for insects. And the Tamron 90mm for fungi, and flowers.