The lens is not that hard to use. A decent workflow makes a huge difference. What is described here works well for 10X microscope objectives, too, which can be mounted on a filter ring using a regular lens as a tube lens.
First, definitely start by using a tripod as hand held is ridiculously hit-or-miss. Learn what
working distance is relative to magnification (I posted a quick guide on photomacrography.net, search for my scottburgess handle there around June 2013). Center the lens and camera on a rail on the tripod. Decide the approach vector and framing of your subject. Match the framing to the appropriate sized colored rectangle on the quick guide, which tells you how to set the magnification on the lens. Place the tripod from the chosen approach vector as close to the given working distance from the subject as possible--the guide has working distance too. Then slide the lens a tiny bit along the rail to focus. After a little practice, this will become reasonably fast to step through. Because you've got the entire tripod almost correctly placed to begin with you won't have problems with heavy gear cantilevered away from the center of gravity which causes the whole mess to sink in some odd direction or vibrate uncontrollably when the shutter trips.
Second, depth of field is very limited due to diffraction. At higher magnifications like 4X and 5X, f/2.8 - f/4 is about all you have to work with, and the DOF is in fractions of a millimeter. So think in terms of flat plane slices when composing. Sometimes it is better to shoot at lower magnification and crop.
Diffraction can also be challenging if you work with small pixel bodies. Don't toss that old digital body because it has "too few" pixels!
You will need to use a flash for live critters (and I often use rear curtain sync). There are some challenges as real critters won't tolerate the flash much. Also, the Canon ring flash is not canted on the interior of the ring so it lacks some coverage at 5X.
Occasionally I use a small light tent to control wind when working in the field. I've done macro work in bright daylight and 20mph wind gusts, with the tent yielding soft light on subject and a black backdrop. Or green, or white! Glorious!
I know some people are mentioning focus stacking, but I recommend against investing in that until you're comfortable using the lens and are confident that further work with it will be a significant part of your portfolio. Focus stacking adds some complexity and cost to the proposition, and I find it easier to work with in a studio setup that I've built than in the field.
I love this lens. It definitely rewards those who work steadily and patiently with wondrous images of things not visible to the naked eye. My eyes are starting to get old enough that I am considering doing more of my work with it tethered to a laptop, but that's what the years do to you.
That's a quick summary of what you really need to know to work with this lens. I hope this helps, and good luck!
Should I add that refurbished units are on sale in the Canon shop, at $755? Oh, of course I should!
The GAS made me do it!
