My OIII Filter arrived in the post yesterday, and we had the opportunity to try it out last night for a short while!
Eta Carinae Nebula
Tried "with" and "without" comparisons; the filter really shows a much larger area of nebulous gas and dust than without, and it seems to provide an almost "3D" depth to it! Very nice!
M42
Similar results to above, I also noticed it seems to make the nebula appear more "fan" like. The Trapezium seemed to be sharper with the filter, though that is likely my imagination!
The Jewel Box
I know it is not for this purpose; I just wanted to see. Turns a nice view into a fairly crappy view!
Very pleased so far; especially as I had to mumble the price into my hand when my wife asked how much it was...
All tested in our 12" Dob, with 30mm Plossl, 20mm wide view, and alternating with 2X Barlow.