Focused UV Source for Cyanotypes?

[Bandicoot]

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:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=270251500292

(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?

Thanks!



Peter

[Jim Noel]

How do you intend to focus UV wavelengths? Do you have a quartz lens? Most glass absorbs UV radiation.

[Akki14]

Why do you want focused? Get a facial tanning unit (a very small tablestop version of a sunbed for tanning of the skin) and prop it up on both ends with stacks of books, face down. That's all I use for my cyanotypes and it's fine for up to 8x10.

[keithwms]

The thing you linked to may work but it looks to me like it'll have a pretty odd radial intensity distribution. Maybe it's fine.

A deuterium lamp will give you lots of juice down past 200 nm and you can easily collimate / focus it. Normally you buy them in a little vented, mirrored housing with a fused quartz objective. If you do this then be sure to get an ozone-free bulbs, otherwise you have to worry about ventilation.

http://www.newport.com/Oriel-Apex-De...3/catalog.aspx

(you can find cheaper used ones, these are commonly used in labs such as mine and in industry; ~$1k would buy you a very compact and fairly high output source)

[Dave Miller]

Keith, I think the key word in the opening thread was: cheap!

[keithwms]

Oh alright

[JBrunner]

An edison socket black light CFL in a spun aluminium clip lamp housing to focus the output a bit might do the trick for the small prints/photograms you describe, as you could place the lamp pretty close.

[keithwms]

Aha I've got you all beaten on cheapness, use the sun and some mirrors or a big lens for a few bucks more....

[Erik Hartmann]

I bought 4 of the lamps witch are being used here.... and build a box ....
So I got a UV-Box witch has been working fine for the last 1/2 year.......exposure time is about 10 min for cyanotypes
But try the lamp.....sure it will work....but put it inside some kind of box.....

[Trevor Crone]

I used a number of these (see link) for my UV light box.

http://www.lightbulbs-direct.com/pro...-saver-25w-bc/

They have an electronic rapid start circuit so they stabilise very quickly.

This company sell other UV lights which might better suit your needs if you are after just one lamp.