Simple. Use a good part of glass.
Start from end. Think about what you want to do. Enormous magnifying? Good depth of field? Print on 15x20 cm photo paper? Fit your screen?
Enormous magnifying is possible with electronic microscope. But, I suppose, you don't mean this. With SLR, you reach best magnifying by use of extension tubes. The depth of field goes under 1 mm and the shutter time has to be over 1 second. You will need a tripod mount and a lot of lights around. I suppose you are not satisfied.
If you mount a common 50 mm or 28 mm lens on objective of your SLR-like camera, you reach 3:1 or even higher magnifying ratio. If you use under 300 mm focus length lens, the subject area is shortened to the dimension of aperture of 50's, the vignette appears so you have to clip the picture as showed here. If you use 300 mm lens with reverse mounted 28 mm lens on it, you'll reach good magnification of 5:1 without vignette! Chromatic aberration in this case is almost not visible.
With common ad-lenses the 1:1 magnifying is best of all you can do. Chromatic aberration is visible on the picture's edges, but sometimes only when is magnified on the screen. Not for profys purposes, but very good tool.
Best results comes by using of original camera's lens if it has good performances. The magnification reaches 1:3 and chromatic aberration is almost not visible.
Example: young seedling of Coryphantha salm-dyckiana taken with Dimage 7 at 200 mm macro with two lenses (2x and 4 x) mounted on it. As the subject is still smaller as available area, the 3x digital zoom was used to spare some disk space. Also, when the image was clipped in this way in camera, almost no computer work was needed. Note that the plant is only 5 mm wide. Fine hairs on spines are undistinguishable to human eye if not magnified.