Filters

[Neil]

G'day everyone, anyone read the piece in Astronomy magazine titled " enhance your observing with filters" ? I was interested in the O-111, really want to enhance my views of M42, and the Hydrogen -Beta filter ,to bring out that ever elusive Horsehead nebula, anyone used these? and how well do they work? Clear skies everyone,see ya.

[Allan]

G'day Neil. I enjoy using filters so much I put a filter slider in my Dob. I've done a few side by side comparisons using the slider.

You don't say what size scope you are using. The H-Beta is generally very narrow and will make the image quite dark in small apertures. They do help a lot in finding the Horsehead, but just as important is a very dark sky and obviously the bigger the telescope the better.

A narrow band/UHC is a good all round filter and will work in any size telescope to increase contrast. That's usually a good one to start with and then get an OIII next for a bigger boost in contrast.

You mention M42 which does look great with the UHC/OIII but my personal favourite is the Carina Neb in a widefield. Very nice

[Amaranthus (Barry)]

The Rosette Nebula looks amazing in OIII. It really does depend on the DSO - they are all slightly different. I regularly use a UHC/LPR and OIII filter. Although the former is meant for light-polluted skies, I find it also brings out contrast beautifully in some structures when observing in dark locations.

[byronpaul (Paul)]

Scope size and type, eyepiece and magnification, as well as light pollution and seeing are some of the elements that will have a bearing on the improvements filters will make.

Whilst light pollution filters can improve what you are seeing, I've been blown away by the improvements Nebula filters make on targets like M42, Eta Carina, Trifid, Lagoon, etc.

I have 2" Lumicon OIII and DGM NPB filters mounted in a slide on an 18" dob. Whilst both vastly improve nebulosity and the ability to expose the fine detail, my preference weights strongly towards the NPB filter for nebula.

Everybodies opinion is different, and there is a great review here on the 2 filters I mention:
http://www.cloudynights.com/ubbthrea...9/Main/5919335

IMHO a H-beta filter is overkill. There are only a handful of targets like horsehead to use the filter on, and unless you have a meg dob and really dark rural skies horsehead is pretty elusive to visual observing. Whilst there are plenty in this forum that have seen Horsehead, I've only had the occasion to really try once with a 22" dob in very dark skies with a h-beta filter. Of the 6 or more of us that looked through the eyepiece, 1 or 2 said they definitely saw it, a couple thought they saw it, and a few of us said we didn't see it

For the price of a h-beta, you can pick up several other filters that you'll get more use out of.

Paul

[Renato1 (Renato)]

I got the O111 before I got an Orion Ultra block (same thing as a UHC). I used that O111 a lot in my 8 and 14.5" telescopes, but it does dim the image a lot. But then I got an Orion Ultrablock and things changed. Nowadays I tend to use the O111 as the filter of last resort when the Ultra block doesn't show me the 10 or 15% or so of faint, point like planetary nebulas - the O111 usually brings them out.

For smaller 5" telescopes, I find my Ultrablock dims the image too much, so I like the broader UHC type filters, like Kson or Astronomik UHC-E filters, much better in them.

In smaller 80mm telescopes, I tend to use the broadband Skyglow or Celestron LPR filters.

As for the H-Beta, perhaps someone can do a service of renting one out, because, apart from the Horsehead, the Comma under the Orion nebula, I think the California nebula (or some other one in that general direction) and another I came across by accident - I've found no other use for it.
Regards,
Renato

[Neil]

Thanks to Allan,Barry,Paul and Renato 1, I found all of your comments very informative and helpful. Allan I have an LX 90 12", Renato 1, the Orion Ultrablock is one filter I hadn't considered, I'll definately check it out, thanks again to you all , see ya.

[Renato1 (Renato)]

Originally Posted by Neil

Thanks to Allan,Barry,Paul and Renato 1, I found all of your comments very informative and helpful. Allan I have an LX 90 12", Renato 1, the Orion Ultrablock is one filter I hadn't considered, I'll definately check it out, thanks again to you all , see ya.

Well Neil, as you get enthused - you'll wind up buying all of them.
With a 12" you won't have a a tough time seeing the Horsehead.
Keep checking the classifieds for good deals.

Cheers,
Renato

[byronpaul (Paul)]

Originally Posted by Renato1

Well Neil, as you get enthused - you'll wind up buying all of them

Ain't that the truth.

Nothing wrong with buying, trying, and selling. Great way to get a good feel for the gear that best suits your needs!!!

[Don Pensack]

There are basically 4 filters that make sense for the amateur looking at nebulae:
1) Broadband. Also inaccurately known as a light pollution reduction filter.
This filter slices out a chunk of the spectrum in the yellow-red area of the spectrum to reduce the glow of the atmosphere from artificial lights. Unfortunately, the effect is relatively minor unless you are already under really dark skies. Even there, the effect is like turning up the contrast a tiny bit. In strong light pollution, so much light bounces around inside the filter that they often make sky glow worse.
Examples:
Orion SkyGlow
Lumicon Deep-Sky
Baader UHC-S
2) Narrowband. This reduces transmission to only a narrow section of the spectrum where nebulae emit energy: Hydrogen emission and Oxygen emission. The Hydrogen emission in the deep red is almost beyond out dark-adapted vision, but there is also a hydrogen emission in the blue *486nm), and the Oxygen emission is nearby in the blue-green (496nm and 501nm). The improvement in contrast is amazing. If you get one filter, this is the one to get.
Examples:
Lumicon UJC
DGM NPB
Orion Ultrablock
Thousand Oaks LP-2
TeleVue Nebustar
3) Oxygen-III filter. Narrower than a narrowband, the hydrogen emission line is eliminated. It improves contrast of small areas of a nebula that emit light in the ionized oxygen wavelengths. Excellent on planetaries and some supernova remnants.
Examples:
Lumicon O-III
Orion-O-III
DGM O-III
Thousand Oaks LP-3
TeleVue O-III
4) Hydrogen-Beta filter (H-Beta filter). Narrowest of all because it restricts transmission to only the 486nm line of Hydrogen Beta. This enhances the secondary ionized hydrogen emission, and makes some very faint hydrogen nebulae more visible (example: IC434 behind the Horsehead Nebula, The California Nebula in Perseus) There are only a handful of objects where this filter is best, but it can do a good job on them.
Examples:
Lumicon H-Beta
Thousand Oaks LP-4

In order of how I would acquire them:
1) Narrowband. The most versatile and "universal" of all the nebula filters.
2) O-III filter. Useful on almost all the objects with strong O-III emission.
3) H-Beta filter. (If you have money burning a hole in your pocket)
4) Broadband filter. If you view at a really dark site and just need to tune up the contrast a bit. If there is any advantage to this filter, it is that it can be used at a little higher power without making the field too dark.

The best magnification to use the filters is 10-12X/inch of aperture and down. Otherwise, the objects may tend to get too dim.

[byronpaul (Paul)]

Don,

I've read your detailed filter essay on your website several times in the past and also countless other threads on filters, but your contribution here is a ready good summary.

Thanks for chiming in

Paul

[Renato1 (Renato)]

Originally Posted by Don Pensack

Orion SkyGlow
Lumicon Deep-Sky
Baader UHC-S

I guess the other thing I'd add to your excellent summary, is variation within the Broad band filters.

My old Lumicon Deep Sky is a broad broadband - only useful at a dark site, pretty ineffective in light polluted skies.

My old Celestron LPR is a narrow broadband - almost halfway to a UHC filter, images are a bit dim in my old lightpolluted backyard.

My Orion Skyglow is between the latter two, very fond of it.

The good thing about these filters, is that if one has the right pair of binoculars, you only need to stick one onto one of the eyepieces with blu-tack to get excellent enhanced binocular views (much better than using a filter on each eyepiece).
Cheers,
Renato

[Neil]

Thanks again Renato,Paul and Don. Your detailed advice is greatly appreciated. Clear Skys.

[ausastronomer (John Bambury)]

Hi Neil,

I gave a presentation at IISAC 2011 on "Visual Astronomy and the use of filters".

Here is a thread on this which has a link to the presentation which you can download as a PDF

Here is a direct link to the presentation PDF

Don and a couple of others have given you sound advice already.

I would recommend either a DGM NPB filter or an Astronomics UHC as the filter you need to start with. They are both excellent but slightly different, notwithstanding they are both narrowband filters. A H-Beta filter is pretty specialised and has a limited number of targets on which it is useful. As Don suggested you buy this after a Narrowband (UHC) and an OIII. A Narrowband like the DGM NPB or Astromics UHC will provide some assistance to see the Horsehead but not as much as a H-Beta. However, the narrowband will provide a noticeable improvement on hundreds and hundreds of targets compared to a handful for the H-Beta.

Don has not mentioned the Astronomics filters. Many people in the USA don't like them, where as most people in Europe do. The Astronomics UHC filter has a somewhat broader bandpass than some of the other narrowband filters like the Lumicon UHC, DGM NPB, and the Orion Ultrablock. This will fractionally limit the filters ability to eek out the last piece of minute detail in the nebulosity itself, but it gives an aesthetically more pleasing view when viewing emission nebula with embedded clusters, like Tarantula (NGC 2070) Eta Carina (NGC 3372), Orion nebula (M42), Lagoon (M8), Triffid (M20) and countless other targets of this type. The Astronomics UHC because of its broader bandpass lets more of the background stars through compared to the other narrowband filters, while still providing excellent contrast extension of the nebula and many people find these views to be more aesthetically pleasing than the views provided by the UHC filters having a tighter bandpass. The Astronomics also works slightly better on the horsehead than do the tighter bandpass UHC filters. It's all about personal preference, what view you provide aesthetically pleasing and what targets you like to look at. There is no right or wrong answer and one is not better than the other, they are slightly different and do different things and it's all about your personal preferences. I have both a DGM NPB filter and an Astronomics UHC and they both get a reasonable share of focuser time. However, unlike "most" of the tighter narrowband filters, which are made in Korea the Astronomic UHC is made in Germany and it isn't cheap, particularly the 2" version. On that basis I think you should head straight towards the DGM NPB which is an excellent first filter. Just be aware that if $$$$$$ aren't a concern there are other slightly different excellent options available.

Cheers,
John B

[Don Pensack]

The Astronomik UHC filter (there are two--I'm describing the narrower one) has about 10nm wider a bandwidth than the Lumicon UHC and about 13nm wider bandwidth than the DGM.
I don't think that's necessarily a problem.

I disagree with David Knisely on this one. He has often said there is value in having multiple Broadband filters, but that one should always pick the UHC and/or O-III filter that produces the highest contrast on the nebulae.
I think there is value in having multiple choices for different purposes.

For instance, a wider filter would show more stars (an observer might like that) and only sacrifice a bit of contrast on the nebula. And a wider filter would be usable at a higher power without dimming the overall field image excessively. That reduced dimming could be important in a small aperture, even at low powers. A wider filter might do fine in a larger aperture when the view is already great and you just want to turn up the contrast.

I use two different O-III filters a lot: the Lumicon (12nm bandwidth) and the TeleVue (23nm bandwidth), and for all those reasons.

What advice do you give to someone who can afford only one filter? That's the important question. I think I'd start out with a filter that runs fairly narrow in its category, has a high transmission, yet doesn't clip any of the desirable wavelengths during transmission.
The wider filter doesn't make the nebula invisible though, and your telescope won't break if you use one. I think if one chooses a filter knowing what the filter is, what it does, and how it differs from its competitors, there is nothing wrong with the choice.
But since nebula filters are fairly expensive, going into the choice blind, without knowing what one is choosing, might result in results that are less than might be delivered with another filter.

I do wish the manufacturers spent more time giving us specifications like bandwidth and transmission percentage averages at the important wavelengths instead of idealized transmission curves.

[ausastronomer (John Bambury)]

Originally Posted by Don Pensack

For instance, a wider filter would show more stars (an observer might like that) and only sacrifice a bit of contrast on the nebula.

Agree 100% Don

Originally Posted by Don Pensack

And a wider filter would be usable at a higher power without dimming the overall field image excessively. That reduced dimming could be important in a small aperture, even at low powers. A wider filter might do fine in a larger aperture when the view is already great and you just want to turn up the contrast.

Agree 100% again

These are the exact reasons the Astronomics UHC sees a lot of use in all my scopes, from the 10" SDM up to and including the 18" Obsession. On targets like the Tarantula Nebula with a lot of embedded stars it is the filter of choice in providing the most aesthetically pleasing view. Unfortunately Dave Knisely has blinkers on when it comes to filters and he presumes that the narrowest narrowband filters are the only ones which will work, without considering that people might be viewing different targets and trying to achieve different goals to what he is.

Originally Posted by Don Pensack

The wider filter doesn't make the nebula invisible though, and your telescope won't break if you use one. I think if one chooses a filter knowing what the filter is, what it does, and how it differs from its competitors, there is nothing wrong with the choice. But since nebula filters are fairly expensive, going into the choice blind, without knowing what one is choosing, might result in results that are less than might be delivered with another filter.

Absolutely and the reason I recommended the DGM NPB as the best choice for a 1st filter. It is about the tightest of the narrowband filters and one of the cheapest to boot. Myself, Mike Salway and David Hough were actually the first people to bring a DGM NPD into Australia when I purchased them directly from Dan McShane at DGM Optics, long before the rest of the astronomical community knew what a good thing they were. If cost is not a consideration there is certainly room in the tackle box for both a DGM NPB and an Astronomics UHC.

Originally Posted by Don Pensack

I do wish the manufacturers spent more time giving us specifications like bandwidth and transmission percentage averages at the important wavelengths instead of idealized transmission curves.

Agreed.

Cheers,
John B

[astro744]

Originally Posted by Don Pensack

I use two different O-III filters a lot: the Lumicon (12nm bandwidth) and the TeleVue (23nm bandwidth), and for all those reasons.

Thanks Don! A lot of people dismiss the Tele Vue O-III for being too broad and not a true O-III (according to one independent test that I have seen), yet I think the Tele Vue O-III filter gives a very natural view with lots of stars but also lots of contrast. I use this combination also on 4", 6" & 10" apertures on various objects and particularly like the view of Eta Carina at low power with the Tele Vue O-III. I do also like the Lumicon O-III for its bandwidth and high transmission which gives great results on planetary nebulae as well as the Veil.

I have actually invested in the Tele Vue, Lumicon, Astronomik and Thousand Oaks versions of the O-III over the years and have only just got myself a filter slide but have not yet done any comparisons other that unscrewing on and off eyepieces in the past. Of the filters I have used, the Thousand Oaks gave me the blackest blacks and whitest whites with a 24mm Panoptic at f6.4 with 10.1" aperture, (Suchting mirror).

However I preferred the view the Lumicon gave me as well as the very natural view the Tele Vue gave me and for this reason I invested in 2" versions of these two filters. Eta Carina is even more spectacular with a 41mm Panoptic and either filter on my 10.1" Newtonian. I think the Thousand Oaks is best for larger apertures >12". I will in due course do a better comparison now that I have a filter slide as it will allow for quicker change between filters. I have not tried DGM NPB or O-III and maybe one day curiosity will get the better of me.

[Neil]

Thank you John, I appreciate all the advice given and effort in your detailed advice, Thanks again.