Well, sometimes it would be interesting to know if there is focus shift for a certain lens. I usually take parts of my calipher and shoot it in VIS and UV and look at the differential. If you don't have something the like handy, a bank note seems to also work well...
This here proves that the well known Noflexar 35mm has hardly any focus shift.
VIS, UV, VIS-UV shot of a 10 EURO bank note at an about 30 degree angle.
[click on image to see a larger one]
Here now an example of a 35mm lens which is quite capable in terms of UV transmission, but shows quite some focus shift:
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