However, it is possible to make a macro lens for yourself. The advantage is that it costs next to nothing. The disadvantage is that it takes some time and if you're not very practical, like me, it presents a major challenge.
However, it's good to know that it's possible. The full article about how to do it is on photocritic.org.
The article also raises some other issues for those of us getting into macro photography. Such as the shallow depth of field and sensitivity of focusing.
One issue I've already come up against, while experimenting, is that of using low shutter speeds outdoors. To improve depth of field I've been using smaller aperatures, which reduce the shutter speed. Unfortuntately because the subject of a macro photography is very small, or being captured in close-up, the slightest movement is magnified.
While I'm usually able to take hand-held photo at 1/15 speed, this is too slow for effective macro photography of plants in outdoor conditions where there is even a slight breeze. The result is a blurred picture.
I need to experiment using a tripod and working with a subject outdoors. That will allow me to identify the slowest shutter speed that's reasonable to use when photographing plants which are subject to gentle wind movement. It will be interesting to see the results.