One of the most important issues to take care of in reflected UV photography is to avoid IR leakage. Here and example why this is the case.
[click on image to see a larger one]
This left image shows massive IR leakage, whereas the one on the right has none and properly shows the black flower center on this Winter Aconite.
and crocus (which is highly IR reflective) here:
The key is avoiding situations with strong sunlight, using a suitable sunhood and especially using the right UV transmission filter, the new 2" Baader U filter in this case, which has a very good IR suppression up to 1100nm. I had already written about that fact in my article: Principle Thoughts about Lenses + Filters for UV
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos