OIII ON M42?????

Hi all, Well my 11 year old Caroline, went out and bought her self with her own money, an 1 1/4" OIII Orion filter for one of our 3 scopes . We had a ultra block but no, that was not good enough she need an OIII. So even with the temp. at 19.3 here in Warwick, NY we took her new starblast EQ ( the smallest of the 3 ) out so she could show my wife and I why she needed to have the filter. It only took but an instant for us to see the difference between the OIII and the ultra block, the OIII showed more of M42 out to the edge of the nebulae but what i found interesting was, that stars the make up the trapezium were at best very very faint if visible at all, but with the ultra block you could see the nebulae nicely along with the trapezium. We were using relatively low power a 24 mm and a 15mm panoptic's. So is my 11 year old wrong about the OIII or is M42 just the wrong nebulae for the OIII.

Thanks for any input

Bob & Caroline

Good for Caroline! Well, you did say you saw more of the nebula with the OIII. I'd say your daughter is right on. Isn't increased contrast of the light from the nebula with broader band light the idea behind a narrow band (nebula) filter?

Wait till you see the Veil and the Rosette through the OIII. Wow!

Hi Bob!
The O-III filter has a narrower band-pass than the Ultrablock, so the background appears darker, thereby making the nebula appear larger and brighter. The O-III also filters out more of the starlight as well, thereby reducing the visibility of the Trapezium. Interesting...but I generally prefer the O-III on most nebulas, but with the Orion Nebula I find I prefer the Ultrablock. Each to his own, I guess...
Larry Seguin
Taos, New Mexico

Try the new filter on your 10" Robert, and tell us what you see. The narrowband filters are perhaps more useful in larger scopes than the starblast. Here's an interesting article on filter comparison on several bright nebulae:
http://pages.sbcglobal.net/raycash/filters.htm

George