I've made a few field-stops for various reasons. My preferred material is thin, black plastic. Some "For Sale", "No Hunting", etc. plastic signs (at hardware stores) are printed on black plastic. I use an Exact-o (hobby) knife to cut out the field stop. Sandpaper will get rid of any colored paints that were used to print whatever message was on the sign (if necessary). The sandpaper will also roughen the surface, transforming it from glossy to flat.
I've made field stops for 2" and for 1.25" eyepieces in this manner. Sometimes a square or rectangular field-stop is more suitable than a circular field-stop . . .
You mentioned specifically 2" eyepieces and large eye-lenses Standby for a short story:
I once had a 2-inch eyepiece (with a very large eye-lens) in the focuser of a reflecting telescope that was being used for some solar observations. After I finished my observations, I pointed the telescope perpendicular to the sun to prevent the (large) primary mirror from focusing a small, concentrated disk of solar energy onto some flammable surface. I'm no dummy. Or so I thought!
The eyepiece had a home-made, rectangular, plastic field-stop precisely at the focal-plane of the eyepiece. I happened to look back and noticed some smoke coming from the long, wood OTA. A very quick glance at the telescope/eyepiece/sun geometry was all that was needed to determine what had happened. The eyepiece was pointed at the sun! The large eye-lens collected enough solar energy, focused it on part of the plastic field-stop, and started melting the field-stop!
So, be careful with those large eye-lenses!
Edited by Sketcher, 18 March 2019 - 03:19 PM.