I've been thinking for a while about a cheap UV source for contact printing on cyanotype. I want to use it for some teaching so it needs to be portable and I'm also interested in something that is more like a point source than the usual 'UV lightbox' construction. The latter point because I want students to be able to use it for photograms and not be restricted to 'flat' subject matter: something a bit 3D like a dry seedhead casts a wonderful shadow, but only if the light is close to a parallel beam.
I don't expect a truly focused source (and I know how I'd build one if I did anyway) and illumination falloff isn't going to be an issue because the prints will be mostly postcard sized and probably never bigger than 10x8 so the lamp doesn't have to be all that far away for fall-off to be negligible.
So, I was wondering if something like this would work:
(This is an eBay listing, only because it was quick and easy to search, I'm sure there are lots of other places I could find something like this.)
Anyone have any ideas as to whether this sort of tube will produce the right wavelengths, and whether a 25W tube at a distance of a foot or two is just going to make for too ridiculously long exposures?
Any other suggestions?