Here are a few more southern ones that show difference between the visible and H-beta (486.1 nm) responses. I know of about dozen more, but I'll have to delve more deeply. I can recall that some of the obscure emission nebulae in Carina and Vela have had reports of observation using H-beta filters. (Astronomical Objects Southern Telescopes 2, I think mention them too)
- Les mention NGC 6334 / Cat's Paw is certainly one
- M20 - Trifid Nebula nebula looks larger to me.
- Doesn't work well on the M42 Orion Nebula, though M43 jumps back at you. Some portions of Barnard's Loop
- IC 410 - Greatest improvement than most
- Murders most planetary nebulae - except the rather dusty or very old ones.
- Some blue stars - Beta Crucis, Beta Canis Majoris
My off the head southern hit-list is...
- IC 2631 11 09.9 -76 37 Chameleon Emission Neb
- IC 2944 "Running Chicken Nebula" 11 36.7 -63 02 Centaurus Emission Neb (Around lambda Cen)
- He2-73 / Sa2-80 11 48.7 -65 08 Planetary Nebula
- Gum 45 / RCW 69 Centaurus 12 44.1 -62 29 Emission Neb
- MyCn 18 / He2-95 Musca 13 38.1 -67 23 Planetary Neb
Best negative response ever is
NGC 1514 in Taurus - the nebulosity disappears completely!
Comments:
- One huge omission in the northern list is NGC 7635 - The Bubble Nebula in Cassiopeia. It shows some extra structural differences without too much dimming.
- You are recommended to need a large exit pupil to make these filters effective
- Read Jack Marling's article on filters at
http://home.earthlink.net/~astro-app...ad/Marling.htm
- The original article on this appears at;
http://pages.sbcglobal.net/raycash/filters.htm