RONCHI

Inkjet and Laser printed Gratings

Copyright – P. J. Smith

But permission is given to distribute this material in unaltered form as long as it is not sold for profit.

Gratings made on transparency material by Laser and Inkjet printers.

Approximately 50 line pairs/inch.

laser printer blank film inkjet inkjet-darkfield

Often recommended by well-meaning people is to make gratings using readily available computer printers.

My experience with this is in general quite negative and I consider it the least useful of all options although it did lead to some interesting research on phase gratings.

The Laser Printer.

I produced good artwork many times larger than needed using an inkjet printer and asked a commercial organization to Laser Copy this on reduced scale on transparency material. Originally the aim was to reduce this again but results were obviously so poor this was abandoned.

Photograph A shows the result. This is close to 40 line pair/inch. Toner particles are clearly visible and it is obvious that if the process were continued, a 100 line pair/inch grating would be very poor.

Maybe there are much better Laser Printers, but, since there are superior common alternatives available, it seemed a waste of time to continue this approach.

The Inkjet Printer.

There is material on the web which encourages making ones own gratings by downloading and printing a file. This is supposed to make a 100 line grating for Ronchi Testing. When I tried this approach the grating was actually 50 line pair/inch which is hardly fine enough for good results.

Photograph C shows the results on my inkjet printer under a microscope. When examined by transmitted light the lines are almost invisible. To make matters worse, after a week in a hot humid climate the ink diffuses making edges even less distinct. By a mix of dark field and transmission lighting the microphotograph at D does show the inkjet lines much better. But the bottom line is that these ‘dark’ lines are an anaemic transparent grey.

When used in a Ronchi test the surprise was that a Ronchi pattern was visible although there are much better common materials available.

Consider the Ronchigrams below.

The 50 lp/inch grating is really not sensitive enough for this very defective mirror.

Used with a slit the results are almost useable. The grating/grating results are hopeless.

Those following much of the advice on the Net about Ronchi testing using this technique are seeing only a very poor sample of what Ronchi Testing can do.

Despite this, the experiment with an Inkjet printer led me to consider why such an apparently poor grating could work at all. This led to an investigation of phase gratings.

Phase gratings are very interesting although in the implementations available to ATM’s somewhat limited.

GOTO RONCHI INDEX