Actually, it really doesn't matter which you use. The first problem is
getting the printer to do equally sized lines and this is difficult to do
with a printer being driven by a windows type program. The only real way to
control this is to use the printer language directly to draw the lines.
Next is that the dots (sort of round but not entirely so) drawn by the
printer will not make a good line so you are reduced to drawing lines of
several dots wide in order to keep the percent error of width of the line to
a reasonable figure.
Much better if you plan on making accurate gratings is to make a grating
engine. This is basically a step and repeat machine that draws lines across
a material with a lot better accuracy. Drawing etched lines across a glass
plate and then filling the etched part with India ink will do a lot better
than any piece of acetate or mylar with dots of a printer on it will ever
do. You will also be able to do a lot of Ronchi gratings for your friends
and sell them to the community as well.
Another method is to make up a large image of the lines and photograph them
but that runs into problems with very large images as negatives get
relatively expensive as the size goes up although the printed circuit board
industry has some fairly low cost film available with the laser printers
that will allow for the smooth lines needed for the job.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!