Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Robert LaBudde <ral@p...> wrote:
>
> At 02:19 AM 10/17/2005, Leon wrote:
> > >>Why do you need a laser? A UV LED with a collimating lens should be
> > >>sufficient. You don't need coherent light, and the only
advantage then to
> > >>a
> > >>laser is the smaller beam divergence initially.
> >
> >UV LEDs don't have anything like enough power.
> 
> What's the power requirement to expose a photosensitive board?
> 
> Remember a 5000 millicandela LED will focused down to a 0.0254 mm point.
>

It becomes a problem of parallax error.

http://www.polyphoto.com/tutorials/LaserTag/ParallaxError01.pdf

You can reduce the apparent size of the source by either cutting off
the end of the LED flat, moving it further from the lense, or choking
it off with a pinhole.

It seems to me someone calculated all this in the past and it came out
to taking a ridiculously long time to expose a board this way.

Steve Greenfield