CLS or UHC?

[Franklin]

Hi, I'm new on here and have a question to ask. If you could only choose one filter, just for visual use from a suburban site with an average scope, to help with light pollution and increase contrast on the greatest number of different celestial objects, which one would it be? CLS or UHC. Which one is the best all-rounder?

[John]

I'd go for a UHC personally and add an O-III in due course.

I've tried a few CLS / Skyglow / broadband filters and found them rather innefective to be honest with you.

 

[Victor Boesen]

1+ for UHC and OIII. I've also tried a CLS filter but I've found that a UHC brings more contrast to the object and OIII can in some scenarios outperform the UHC by a noticable amount.

[Franklin]

Hi John, thanks for the reply. I've been reading a lot of your input on this site, very knowledgeable. Yes UHC that's what I was thinking too. I have a Baader Neodymiun Moon & Skyglow which does help with contrast on solar system objects but I'm looking for a filter for deepsky viewing now. My scope is no light bucket, 127mm f9.4 achro, so I think the narrowband O-III and others might be lost on it. Which is why I'm after a general purpose "nebula filter". My mind was all but made up on the Baader UHC and then I read on some of the sales sites how the CLS will perform on a greater number of deepsky targets. Hence my confusion. Anyway, from the posts I've been reading on here you seem like you're one of the resident guru's so I will side with your advice, especially since you have experience with refractors. Baader UHC it is.

[Franklin]

That's a second vote on the UHC then. Thanks Victor.

[John]

Just be aware that the Baader UHC-S (if that is what you have in mind) is really a broadband filter. It has a much wider band pass width than other UHC's. I think a "conventional" UHC such as the Orion Ultrablock or Astronomik UHC would be a better choice.

I find an O-III pretty effective with my 100mm and 102mm refractors.

 

 

[Franklin]

Yes, that was another point I picked up on from a post on the CN forum. UHC-S? What does the S mean? Is it that the filter allows more of the total spectrum through? More than a conventional UHC.  So if that is the case the Baader UHC-S might be not too different from the Skyglow I already have. What do you think of the Explore Scientific range of filters? They do a 2" UHC. Would that be like the Baader UHC-S or tradtional UHC? There's so many filters out there, I'm confused.

[John]

The Baader UHC-S was designed for small aperture scopes (smaller than yours) and does allow a wider bandwidth through than a "normal" UHC which makes it more like a broadband / skyglow type filter.

The Explore Scientific UHC is would be a better choice but an Astronomik UHC or a Orion Ultrablock is better again.

If you come across one, I have found the older Meade 4000 Nebular (that is how it is spelt !) Narrowband filter really quite good (better than the Explore Scientific) in my 100mm - 130mm aperture refractors. These are out of production now but turn up on the used market at quite good prices.

The Castell filters have a good reputation for their relatively low cost as well although I have not actually used one myself. As you can see from the chart here the Castell UHC is closer to the Astronomik UHC in it's band pass width and more "aggressive" (therefore more effective) than the Baader UHC-S:

https://www.365astronomy.com/castell-uhc-ultra-high-contrast-filter-1.25.html

 

[Franklin]

Thanks for the link John. I've been on 365 loads and never seen that before. It's good to see all the spectra for the different filters side by side like that. Wow, how little the Neodymium cuts out! The Castell UHC looks very close to the Astronomik like you said so that could be the one. Thanks for all your help.

[Ricochet]

10 hours ago, Franklin said:

Hi John, thanks for the reply. I've been reading a lot of your input on this site, very knowledgeable. Yes UHC that's what I was thinking too. I have a Baader Neodymiun Moon & Skyglow which does help with contrast on solar system objects but I'm looking for a filter for deepsky viewing now. My scope is no light bucket, 127mm f9.4 achro, so I think the narrowband O-III and others might be lost on it. Which is why I'm after a general purpose "nebula filter". My mind was all but made up on the Baader UHC and then I read on some of the sales sites how the CLS will perform on a greater number of deepsky targets. Hence my confusion. Anyway, from the posts I've been reading on here you seem like you're one of the resident guru's so I will side with your advice, especially since you have experience with refractors. Baader UHC it is.

A good site for filter comparisons is https://searchlight.semrock.com/?sid=a08a1af9-84ee-49d2-959d-153d7e7c0eb8

I think this shows the differences between filters better than the pictures on the Castell page. From a suburban site I think a narrower passband will be even more beneficial than at a dark site as it cuts out more light pollution. I certainly wouldn't dismiss OIII filters based on aperture, you just need to be mindful of exit pupil and that you will need long focal length eyepieces to generate the required exit pupil with your scope (i.e. >32mm).

[Franklin]

Got the 2"Castell UHC and am very happy with it. Just need to get a Cloud dispersion filter next!

[vlaiv]

17 minutes ago, Franklin said:

Just need to get a Cloud dispersion filter next!

I'm afraid you are out of luck there, but here is alternative:

https://www.firstlightoptics.com/misc/zarkov-cloud-gun.html

It is a bit expensive, but I'm told its worth every penny.

[Franklin]

Got to get one of them. Lol.

[Louis D]

On 25/07/2020 at 17:14, Franklin said:

I think the narrowband O-III and others might be lost on it.

It's really exit pupil dependent, but even at smaller exit pupils, it's quite helpful on many emission nebula.  Just start with large exit pupils and move your way up in power to see the effectiveness or lack thereof at smaller exit pupils.

For galaxies and comets, there's no substitute for dark skies.

Globular clusters need lots of magnification to resolve them.

Many planetary nebula do fairly well at high power without filtration.

Open clusters are of such high contrast that they are fine without filtration as well.

[Franklin]

I'm new to "nebula filters". Just got a UHC, not much use yet, but I did have a quick look at the Ring and Dumbbell planetary nebulae with it and there was noticeable improvement. The background sky was darkened making the objects appear more defined. From what I've been reading an OIII would work even better. On my xmas list.