A popular way to photography objects at these scales is to use objectives from transmitted light microscopes.
FAQ: How can I hook a microscope objective to my camera?
The key thing here is knowing that there are two types or designs of microscope objective. Finite (finite conjugate) objectives are fairly easy to use, they just need to be mounted at the end of a bellows and they will form an image at the distance (typically 170mm) for which they are designed. Infinite (infinite conjugate) objectives expect a relay lens. Many newer objectives are of the infinite variety and are marked with a distance (such as 200) along with the infinity symbol, which I found confusing. The story is that the number (such as 200) is the expected focal length of the relay lens, the objective is indeed an infinite conjugate objective when so marked.
Apparently an infinite conjugate objective will form an image without a relay lens, but it will be inferior to the image obtained when a relay lens is used. The usual scheme is to mount the microscope objective in front of a telephoto lens of the necessary focal length. Zooms are not ideal, but may work just fine, particularly if used at the longer range of their zoom capability.
The other bugaboo is chromatic aberration. Some objectives do not fully correct for chromatic aberration, expecting it to be compensated for by some other part of the microscope for which they are designed. Such an objective will not perform well (to say the least) for photomacrography. There is apparently no way to predict how this will work out with an objective that has not yet been tried out by somebody.
A lot of people have had excellent results with certain Nikon microscope objectives, and a lot of information can be obtained by reading the information in this link.
This link begins with a discussion of the setup used by Charles Krebs, who has taken many amazing photographs. Within the thread is a collection of links to many different setups, and each is instructive.
This link begins as a discussion of Nikon, Olympus, and other focus blocks, but has developed into an extensive discussion of equipment for photomacrography.
There is lots more amazing information on this site. It rewards careful study and does not yield its best treasures on the first visit.
Here is a great discussion on different lenses, aperture, and stacking.
The tests described indicate that one fellow gets the best resolution from the MPE-65 using it at f/2.8 (fully open), whereas the series of tests done by Charles Krebs indicated that f/4.0 was the best. The conclusion is that you had better test your own lens and camera setup to see what is best for your equipment!
Charles Krebs says that he never uses it stopped down smaller than f/5.6 at 4x or more magnification (this gives an effective aperture of f/34 or so). Mr. Krebs has used the MPE 65 with the Canon 1.4x converter (and a short tube) with good results and feels that is the thing to do if you want to get more magnification than the lens by itself can give.
Here is another lens shootout from a different site: Macros Muy Macros They are testing lenses on a full frame camera and like the Mitutoyo 5x and the Olympus 38mm. Of particular interest is a flash based image comparison tool written by John Hallmen. (email@example.com) see: this link.
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