Hi all , I was wondering if someone could tell me what my options are filter wise. I have bought a starshoot 5 filter wheel. I have an Orion LRGB filter set , a televue Nebustar filter, and a Lumicon Hydrogen Alpha filter. I wanted to load the Nebustar and Hydrogen alpha, along with the RGB`s . I only have 5 spots , so I was wondering if I could use the Hydrogen alpha in place of the Luminance , and also , can the Nebustar be useful in Imaging or is it really just for visual use ? Thanks to all

I'd drop the Nebustar as it is mostly a visual filter and apparently blocks H alpha in emission nebula. It probably only passes H beta and OIII spectral lines greatly dimming stars to help certain emission nebula when seen visually. Most of these also emit H alpha making that filter a better choice for them as that emission line is usually stronger than the other two combined but poorly seen by the human eye. Both would severely dim star fields and galaxies over a luminance filter.

H alpha is can be used for luminance filter ONLY with emission nebula. Even then it requires extensive exposure time, I use at least 3 times more than I do luminance, 4 or 5 is better. You are only passing a very tiny part of the spectrum so are throwing away 99% of the light of broad spectrum objects like stars and galaxies but passing a significant portion of it for emission nebula. Note reflection nebula, often associated with emission nebula will be lost however.

It is very good for such nebula in light polluted skies. You don't say what your sky is like. It is also useful for some galaxies that are rich in H alpha like M82 but only to augment the luminence data not to replace it!

In my 5 filter wheel I use luminance, red, green, blue and H alpha. But I live under very dark skies.

If imaging from within Winnepeg's light polluted skies you may want to focus your attention on emission nebula and forget the LRGB filters replacing them with SII, H alpha and OIII filters. That's considered the best solution to heavily light polluted skies. But does limit you to emission nebula but that still leaves you a lot of targets.

Rick

Hi Rick , thanks so much for the info. Light pollution wise , I live in south Winnipeg, just beyond the perimeter highway, and have a back lane behind me, so it is not too bad .I`m right at the edge of the city so when i`m looking in the south sky i`m ok , but anything north is much worse. I also share a cottage with my brother in north western Ontario, 10 mins past the border and the skies are jet black , but I havent had the big scope out yet .( 254 N EQ-6) Just got it in end of may.

I just bought a StarShoot 2 Monochrome imager and a Star Shoot autoguider ( Visa sure loves me )which I hope is a decent starter camera to learn on ? Also , even though I researched the Tele-vue Nebustar before I bought it , I kind of wish I would have spent the money on an OIII filter. Has anyone ever tried imaging a couple of shots through a Nebustar ? When you look through it ,it is a mostly green , small blue tint to it .

Thanks again for your help , Jim

I don't find a light curve for the Nebustar but they claim it equivalent or maybe "better" than the Lumicon UHC. That light curve is on the net. Note it only passes the H beta and OIII lines blocking the rest of the spectrum. Objects not emitting mostly in this part of the spectrum will be greatly dimmed by such a filter. CCD cameras while having a peak response, some in the blue green some in the red have a response curve far flatter than the human eye which peaks in the blue green. Thus for visual use such a filter greatly enhances many emission nebula by reducing sky glow and star light but passing the main light emitted by the nebula that our eye is sensitive to. Since we see these in black and white the color is usually lost though some really bright emission nebula do look rather blue green in the filter, M42 and M17 for instance. For black and white photography it would work for such objects but since they emit far stronger in H alpha (but our eye's see this very poorly making such a filter nearly worthless visually) a H alpha filter is normally far better for such objects. Eyes want the UHC, cameras H alpha.

Here's the Lumicon version's response curve. I'd expect it very similar to the Nebustar's response curve. Note the curves stop before H alpha is reached. I believe the Lumicon version passes some H alpha but Nebustar's doesn't based on the Nebustar claim of it being "Red cut-off". In our club members with very old Lumicon UHC filters report no H alpha response but those with more modern ones do report H alpha response but it varies greatly depending on when they were made. Still for CCD work the pure H alpha would give the highest contrast for such objects and is preferable.
http://www.lumicon.com/images/lumico...hart-revsd.jpg

Rick

Hi Rick , thanks so much for all your help and information , greatly apprieciated
Jim