Regarding the macro lens question... better images, no. The EF-S 60mm Macro lens is smaller and lighter, more compact and portable than either of the Canon 100mm Macro lenses. However with a shorter focal length, you have to work a little closer to your subjects. So the longer lenses might allow you to shoot subjects that are too shy to allow you very close, or help prevent accidentally throwing a shadow over your macro subject. But really there will be little difference in image quality. The EF-S 60mm has excellent IQ.... As do both the Canon 100mm macro lenses. The 60mm's autofocus might even be a little faster than the 100mm lenses (all macro lenses tend to focus a little slower... they are "long throw" focus designs, to emphasize focus accuracy over speed... plus they have to focus all the way from infinity to 1:1 magnification, moving their focus group a long, long way).
The 100L has IS, which you might find most helpful if you using the lens for non-macro purposes, where the stabilization may give the equivalent of 3 or 4 stops of assistance (allowing sharp shots handheld at 1/25 shutter speed, for example). At high magnifications (near 1:1) don't expect as much assistance.... maybe the equivalent of about one stop (maybe allowing 1/80 or 1/100 shutter speed).
The 100/2.8 USM (not the L/IS) sells for a lot less and doesn't have IS. Image quality of the two 100mm macro lenses is about equal.
I particularly like the Canon 100mm macro lenses because they can optionally be fitted with a tripod mounting ring. Most lenses this focal length and shorter don't offer that option and I find the tripod ring very useful for macro shooting.
But I also use a 60mm macro lens, for it's smaller size and portability. I take it in my camera bag when I don't know whether or not I'll be shooting macro, but want it handy just in case. On the other hand, if I'm out with the primary intention of shooting macro I carry the 180/3.5L, 100/2.8 USM and MP-E 65mm macro lenses (the last is an ultra-high magnification, manual focus macro lens), along with macro flashes MT-23EX and ML-14EX.
Regarding your telephoto zoom...
The 100-400mm f3.5-5.6 zoom can be fitted with a teleconverter, but you will lose auto focus on both your cameras. A 1.4X teleconverter would make that zoom an effective 140-560mm f5.0-8.0, and your cameras are only designed to focus with f5.6 and faster lenses (Canon 1D series and 5D MkIII can focus to f8). Adding a 2X would be ever worse, costing two full stops of light and making the zoom an effective 200-800mm f7.1-11. There are some work-arounds... such as manually focusing. You also can tape over a couple of the contacts on the teleconverter, so the camera doesn't know it's there and still tries to focus, just don't expect it to be very fast.
Also, in generaly teleconverters work better, give nicer image quality on prime lenses rather than zooms. A 1.4X on your zoom might not be too bad. But a 2X likely might not give satisfactory image quality.
But, hey, 400mm is already a whole lot of lens on your cameras! You might try a teleconverter.... or just work at get ting closer to your subjects. Part of the fun and reward of wildlife photography is getting close enough to get the shot (safely, of course).
I spent three months getting acquainted with this coyote to the point she'd sit nearby or even lie down and fall asleep within arm's reach, and was rewarded with lots of photo opportunities. These two images were shot with a 135mm lens (on 7D)....
Those opportunities are rare, though. Often I carry a Canon 300/4 IS lens, which does happen to work well with a 1.4X teleconverter. The image below was made with the 300mm lens alone, once again on a 7D...
Same lens and camera for this one...
The image below was shot with the 300mm plus 1.4X (on a 5D Mark II)....
There can be opportunities with captive subjects, too... Following was shot with 70-200mm lens, on a film camera (i.e. full frame), at a neat safari-style zoo in Oregon...
Work on your stalking skills, use blinds, use calls and attractants to get the critters to come closer to you. Look for locations where the animals frequently feed or relax and are approachable. In parks where there are a lot of people birds and animals will often let you get pretty close, too.
Your car can be used as a blind... animals often allow a car to slowly approach pretty closely. Below image was shot from my car window, with 300mm lens (on a film camera)...
Yes, I do use longer lenses sometimes. Enough to know that no matter how long a lens you have, there will always be wildlife subjects that are just out of reach. Bird photographers, in particular, will tell you there is no such thing as a "long enough" lens! Some subjects will just be too far away... and when they are I figure that's a good time to put down the camera, relax and enjoy the show.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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