Today about using getting rid of vignetting when shooting reflected UV light and using older lenses. The rescue used here is a quartz Balow lens.
[click on image to see a larger one]
UV test image, left without and right with quartz Barlow lens:
White Clematis in UV:
That used Barlow lens enlarged the projected image by a factor of 1.4x, hence letting the vignetting disappear beyond the sensor borders.
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