Off-topic a bit but may be useful:
I have tried many times to get proto. boards etched using transparencies
with poor results. The printers can't get enough toner to stick,
especially on large areas of black (copper).
I now can get suberb results using:
1. A laser that puts down loads of toner (e.g. HP), I have Brothers and
Kyoceras and they seem to to be trimmed for economy (i.e. light toner
usage) which is the wrong thing here, an old Laserjet 4 works fine, as
do 2 modern HP colour Lasers.
2. I stopped playing with transparent film and used simply normal paper.
Providing you take the normal precautions of appropriately mirroring so
that the toner side is against the board, this works very well. The only
downside is that you need more exposure time. I use 30 minutes, where a
film would need about 10.
Just my €0.02
Bob von Knobloch.