Filter for visual deep-sky observations

[astrochumak]

Hello everybody!
Recently I bought myself a new telescope - DOB 8 retractable (yay), and now I'm looking for some DSO filters to help me see a little bit more details
I live in a Bortle 7 area, so there's a fair amount of light pollution out there. After doing some research I was kind of stuck at one point. Some people say that UHC is more aggressive than CLS filter in terms of light passage, but I was unable to find how it affects visual observations. I was wondering if somebody can clarify this for me: considering the level of LP in my area, which filter will be the best all-around filter for nebulae: CLS, UHC, OIII or Hbeta (I'm into galaxies more, but I guess broadband filters won't be that useful in my area)? As a lot of people write "The best filter for DSO is a gasoline to your car", but unfortunately I don't have one.
Clear skies, everybody🙂

Edited December 10, 2020 by astrochumak

[Victor Boesen]

Congratulations on your new telescope, it's a great choice! Deep sky filters will work better with larger apertures so 8 inches is great;)

I've tried a couple of filters throughout the last 5 years or so (From bortle 7/8 at home and bortle 4 and 5 skies abroad) and found that I always return to my OIII filter from Castell. My first filter was a CLS filter, but I didn't find the improvement/change to be that noticeable through the 6" scope I had at the time. As I upgraded to a 10" dob I got the Castell UHC and OIII filters and they were both better than the CLS filter in my opinion. The stars and background aren't as bright but the nebulosity is a lot more evident. Comparing the UHC to the OIII they're both very useful, but I'd say the OIII is better at more light polluted skies because of its narrower pass-band. At bortle 5 skies the OIII has helped me spot the western and eastern veil nebula (Through my 4" refractor) which I wasn't able to locate without the filter.

If you expect the filter to work for galaxies I'd go for a simple light pollution filter since they are rich in natural light (eg. stars, so you don't want an OIII- or UHC filter which dims the stars).

I have a couple of sketches of M27 comparing the view with and without my OIII filter from home which you can find here (The comparison is mentioned in the observing notes). You can also find my sketch of the eastern- and western veil from the bortle 5 location with my 4" scope:
https://myastronomyjourney.wordpress.com/my-astronomy-sketches/

I found this chart quite useful when choosing what filters to get:

Victor

Edited December 10, 2020 by Victor Boesen

[astrochumak]

1 hour ago, Victor Boesen said:

Congratulations on your new telescope, it's a great choice! Deep sky filters will work better with larger apertures so 8 inches is great;)

Thank you so much, Victor, for your reply, it was really helpful! Will look into OIII filters then. Great sketches by the way!:)

[Victor Boesen]

1 hour ago, astrochumak said:

Thank you so much, Victor, for your reply, it was really helpful! Will look into OIII filters then. Great sketches by the way!:)

No problem, glad I could help:) And thank you very much

[PeterW]

UHC or OIII, CLS isn’t aggressive enough and h-beta is very aggressive and is only noted to work well on a few objects. Darker skies are best, but if you can shield yourself from direct lights, dark adapt and shield/flock your scope you can gain something back against the light.

Peter

[John]

I agree with the above - a good quality UHC or O-III. Usually the advice is to go for the UHC first but personally I've found the O-III makes more of an impact. Having both in due course is the ideal of course 

I use these filters often with 100mm scopes so you don't need big apertures to get benefits from them

 

[tripleped]

Interesting and informative discussion. My question is with the terrible skies where I live (Bortle  8 ) and even though I have a 10” DOB how much can I really expect from either of these filters mentioned? Often the Amazon descriptions talk about “amazing” results but with my skies I find that hard to believe. Just don’t want to start chasing filters if the benefit would be marginal. Thoughts?

[John]

19 minutes ago, tripleped said:

Interesting and informative discussion. My question is with the terrible skies where I live (Bortle  8 ) and even though I have a 10” DOB how much can I really expect from either of these filters mentioned? Often the Amazon descriptions talk about “amazing” results but with my skies I find that hard to believe. Just don’t want to start chasing filters if the benefit would be marginal. Thoughts?

Such filters do benefit from dark skies and are more effective under them than they are under light polluted skies. For an observer trying to observe nebulae under bortle 8 skies, which is a pretty challenging proposition, the filter might be the difference between seeing some suggestions of the target and seeing nothing at all.

 

 

 

Edited December 26, 2020 by John