Homebrew PCBs

Hello...

Does someone know what energy is nedded to develop photoresist?
I thinking to make an atacchment to CNC to make something like 
photoploter(imagesetter) to develop direct pcb not film. Ie some lamp 
and lenses to make beam paralel and adjustable apprture (iris).
And when 'drawing' line the aperture is oppened to make trace of light 
of just correct width.

Now I'm stuck as I can't find data of different photoresist. I know that 
near all of them need UV light of aprox 400nm wavelenght.

I know that few people try similar with laser. But near all fail in 
presision. With laser the photoresist make buble as in developing 
process the nitrogen gas is released from photoresist. So we need lower 
energy.

So does someone have data for photoresists? And maybe some idea how to 
realise optics?

Thanks

Slavko