In my quest for studio perfection I decided I should like to upgrade my ultra violet exposure unit.
Those familiar with alternative photographic processes will be aware that a UV light box is a pretty common tool. It is used to expose whatever you're printing onto/with to UV light which when passed through a negative onto a pre-prepared light sensitive surface can produce an image.
My own UV box was okay. I built it myself and it had been slowly upgraded and tweaked over the last six months and did a decent enough job. It had a vacuum driven contact frame which I was very proud of and could hold a sheet of paper up to 600mm square. the only thing I wasn't happy with was the exposure times, which were a very lazy 25minutes that impacted upon my work-flow and rather stressed my vacuum pump.
With this in mind I began looking into how to improvements. My initial idea was to increase the amount of UV florescent tubes from 6 to 14 and increase power and efficiency by over-driving the tubes and using modern high efficiency ballasts. However before I did this a fairly new technological advance, namely ultraviolet LEDs caught my eye. Having found that you can buy them, ready-to-go, on a 5m long ribbon I decided to buy a length and jury-rig a test. The results from this rough test were surprising - a very good and even exposure in less than ten minutes. Hearted by this I shelved my UV tube ideas and set out to build an LED based unit.
I purchased an extra 5m of the LED ribbon and and set about cutting it and attaching it to a white foamex board.Once finished I had a UV array consisting of in excess of 640 LEDsWhilst housing the new LED panel I took the opportunity to improve my existing UV unit box, slimming it down and generally tidying it up. I fitted out the inside with white foamex to more effectively reflect the light and moved the vacuum pump so it could be mounted externally to prevent heat soak into the vacuum frame and stop it blowing dust around inside the box.
For added ease of use I also integrated a timer unit, which allowed me to pre-select a time, hit the start button and let it go.
So how is it? ...
All in all I'm very pleased. It's a much neater set-up and a dream to use. It runs cool and uses less power. The only issue I've found is that the LEDs seem to be producing a slightly lower contrast image. I assume this is due to the longer wavelength of emitted by the LEDs compared to the UV tubes (405nm against 375nm), though I'm not sure of the physics involved, but I should be able to compensate for that.
Here's a little vid of it running.UPDATE. Surprisingly the move from tubes to LED has meant that I have had to produce new Photoshop adjustment curves for the printing of my digital negatives. I can only put this down to the manner in which the longer wavelength UV light emmitted by the LEDs penetrates the film and ink of the printed negs. However once the adjustment has been made it is all working great.