For live specimens, the 100-400 will give you a lot more reach, of course, compared to the 100 macro. It also has very close focus (to about 1:3 life size). It's excellent quality (I have one), but the macro will be a bit sharper. The latter may not be noticeable with handheld shooting.
Yes Danny, I thought the 100 mm macro was most useful fo rdead specimens which I have not any more and the 100-400 mm would help me a lot withother animals such as reptiles, birds, etc.
I have a 105m Macro and for insects such as butterflies I would not exchange for any other lens. For tiny insects, another set up is needed. A Zoom lens should be fine for reptiles, especially snakes. As for birds, unless you can get really close, you will get miniature images, if you are into bird photography you need to get one of those rather expensive long lenses, in fact the greater the Zoom and longer the lens the better.
When I am out and about photographing butterflies in the UK, I can always spot a bird photographer that has recently taken up butterfly shooting as a hobby, he always has one of those very long zoom lens dangling. He has to be some distance away from his subject to get a good shot and as there is nearly always some sort of herbage in the way and perhaps me, not so good. However, if he was out in the tropics trying to get images of canopy butterflies, that is the lens you would need.
I will probably end up with both, but these are rather expensive lenses ! Anywhere, I will learn the equipment on everyday subject such as my dogs this morning and a few plants as the wether was cold and windy today. Then we will see which one is the priority ?
I originally started out using a 60 mm macro lens on my Nikon, but quickly found you have to get too close to your subject to get much in the way of macro.
Fast forward a few years (add a real job that pays better than grad school) and I upgraded to a 200 mm F4 Nikon macro lens. The working distance is at least a foot from the end of the lens when going 1:1. I added a Nikon R1 macro flash that lets me take photos in any light.
Here are a couple examples of pinned specimens indoors. All were hand-held
The first pic is from further away, but as you get closer the background gets further out of focus so that in the second photo you can't really see the foam base even though it's only an inch or so below the wing.
That's a good point. With the crop sensor you're able to stay a little further back.
Another thing that may or may not work, depending on your setup is to add extension tubes that can give you magnifications greater than 1:1. The problem there is that it really takes a lot of light to get a good exposure as you extend. Here's where a good flash system can really help out.