Galaxy portrait upgrades with NB filters: 7 vs 3nm?

[GTom]

The best galaxy images I've seen usually contained H-α, sometimes OIII and SII layers too. I was wondering, do the super-narrow 3nm bandwidth filters have an advantage in this? Guessing, the 3nm variant allows about half the amount of starlight trough compared to a 7nm filter, I'd expect better separation of the otherwise tiny objects.

Going narrower obviously brings up the next challenge: need a filter that performs well with my fast systems (quattro 150p: f/3.45, telephoto: f/2.8 300mm)

Edited Sunday at 03:18 by GTom

[ONIKKINEN]

Distance to the galaxy in question is also a potential issue due to redshift. As an example a galaxy with a redshift of 0.005, around 70 million light years, will have the emitted Ha signal redshifted outside the 3nm bandpass so barely any gets through.

For nearby galaxies, i think the narrower the better assuming there is no bandpass shift from fast optics. Many filters are sold also in high speed variant and work well with fast systems, although usually the cut off point is around f/3 so that reduced quattro is in the potential danger zone of barely passing the light.

[ollypenrice]

I wouldn't say that the best galaxy images I've seen (or taken) have NB data added. RGB captures the same amount of NB data as is to be had through a NB filter. The NB filter allows us to isolate and exaggerate it, though. Still, I have, like most people, added a highly stretched and segregated Ha layer to galaxies in the past, though I've toned the addition down over time.

I suspect that your fast systems make the decision for you: stick to filters guaranteed to work with such steep light cones. I also think that the virtue of narrow bandpass filters is that they bring out finer structural detail in nebulae. At galactic distances and with the resolution of amateur optics, I doubt that these finely resolved details are available anyway, so a broader bandpass will do just as well - except, perhaps, in combating LP or the moon.

Olly

[emyliano2000]

I just finished M33 in full narrowband with 3nm filters.

I shot it in both broadband and narrowband but a SHO-LRGB palette looked a little bit weird so I decided to do 2 palettes, HOO-LRGB and full narrowband in SHO.

I used my 200p telescope with the ASI294M and 1.25" chroma filters.

I can't really say if there is an advantage over the 7nm filters because I never used 7nm filters on galaxies before but I found that I get pretty good results with the 3nm.

I don't usualy shoot Sii for galaxies and only occasionally, when there are large star formation regions, I use the Oiii filter but knowing that M33 has some really big nabulae inside it, I added Sii to see what comes out. For the Sii, I only shot 600sec.

This is the annotated SHO version and below it, the HOO-LRGB version.

Emil

[Ratlet]

Incredible.  Such a large amount going on in the SHO

[GTom]

4 hours ago, Ratlet said:

Incredible.  Such a large amount going on in the SHO

Probably richer than our own galaxy plus the fabourable angle.

Edited Monday at 00:03 by GTom