> >A huge obstacle for me in the past when exposing pre-sensitised PCBs
> >through a printed film was light 'leaking' because the image on the film
> >was not printed on the correct side of the film.  With the film flush with
> >the surface of the board there was still enough light leakage through the
> >thickness of the film (a few hundredths of millimetres?) for the image to
> >be blurred.  I guess what I'm interested in finding out is if anyone has
> >had any practical experience of focussing an LED's beam to close
> >tolerances.  Maybe then I'll give this a go!

So what is wrong with following the KISS principle? (Keep It Simple Stupid)

If you are having a problem with blur because of film thickness,
plot your board 'mirrored' and then flip the film over so that
it is next to the laminate when you expose it. This is why most
board packages have a 'mirror output' function. Remember that you
only need to flip one layer since most packages plot the view
as you look through the board.

If you can use an arc source for exposure you also reduce the
blurring since any shadows are much crisper.

In order to get good lines you have to modulate the LED intensity
based on velocity since it is the integrated exposure time the
controls density.

R

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