Homebrew PCBs

At home I have a Photographic 'Wet' Darkroom (as opposed to a 'Digital'  
Darkroom) and I have often wanted to project UV light to expose some of  
the older forms of emulsion (Cyanotype, for instance).  Conventional  
wisdom has it that this cannot be done with glass lenses as they absorb  
far too much of the short wavelength light.  I have tried a jury-rig  
and it didn't work at all.  I have also observed that if I use a  
plastic negative, of only a few thou' thickness, the exposure times  
double (this is when I use a direct light source).
Now, if someone out there is able to push short wavelength UV through a  
glass lens, or perhaps they have a source of lenses made from quartz or  
some other material that passes UV, I would most definitely like to  
know.
There are sources of special lenses but at a high price only.  The URL  
below is such a company.

http://www.edmundoptics.com/index.cfm

Just a thought,
Simon


On Friday, May 23, 2003, at 09:36 Europe/London, Neil wrote:

> Alright, call me crazy, but an idea just occurred to me, and I can't  
> see why
> it can't work.  To me, the most difficult (expensive, complicated,
> unreliable, etc) part of creating a PCB is getting the pattern laid  
> out on
> the board so it can be exposed, etc.  The rest is science ... standard
> procedure, standards times, standard results.  Yes, laying out the  
> pattern
> can be science, but at a higher price, and still takes time to line up  
> the
> image transparencies, etc.
>
> So this idea just randomly came to me ... why not use a projector to  
> project
> the image on the board.  Use a positive-coated board and an XGA LCD
> projector, with a UV bulb instead of the usual bulb.  I get quite good
> results at 300dpi, so if we go with a projector resolution of 1024x768  
> for
> now, that's about 3.4" x 2.5".  There may need to be some optical
> manipulation done to get it to focus clearly at that distance, and a  
> bunch of
> other little things sorted out (such as calibration for
> non-linear/inconsistent pixel spread), but I can't see why it can't  
> work.
> No, it's not cheap, but I believe it would be really fast, going from
> computer straight to PCB.
>
> Maybe this has been thought of or done already?  Or maybe I'm going  
> off the
> deep end?
>
> Cheers,
> -Neil.
>
>
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Simon Whitehead
s.whitehead@...