Achromatic Close-Up Lenses
If you want to get even closer than your present gear allows, check out an achromatic close-up lens. This is a highly corrected close-up lens, at a fraction of the cost of a macro lens. Canon (look for 250D and 500D models) and Century Optics make good ones that will fit any brand of lens, because these lenses simply screw into the front of your existing lens. You can even get them to fit multiple lenses by buying an achromatic close-up lens that fits the filter ring of your largest-diameter lens, and then getting inexpensive filter-ring adapters to fit your other lenses.
This accessory lens is easy to use because you don't need to do anything other than screw it onto your lens. Then you just focus and shoot. Your camera will work with autofocusing just fine, though you do have to be careful where the camera is actually focusing.
Results will be very sharp, as shown in Figures 4 and 5. This will depend somewhat on your original lens because you are modifying it, but I have been pleasantly surprised to see how well these little accessory lenses work on all sorts of main lenses. I have even used them on compact digital cameras that don't have interchangeable lenses but do have a filter ring.
Figure 4 Small monkeyflower, zoom and achromatic close-up lens.
Figure 5 Flower fly, zoom and achromatic close-up lens.
I will warn you, though, that zoom lenses will not work as you expect, such as allowing you to zoom in and out on your subject. Because of the way close-up lenses work, their effect is related to the focal length of the lens, so that as you change focal length, you will be changing how close you can focus, which then changes your focus as you zoom.
Avoid cheap close-up lenses or “filters” such as those that you can buy in packages of three for $4070 or so. These are not corrected lenses, and they give soft, less sharp results. I can't recommend them unless you want a soft focus close-up. (That can be an interesting effect, but it is just an effect.)