Filter to view nebulae

[atman]

Hi all

I've got an 8" Bintel dob, with just the 3 standard eyepieces + an Televue 3x barlow.

Someone recently strongly recommended getting filters - I am particularly interested in being able to enhance the view of nebulae, (he mentioned hydrogen beta) but in the couple of days of researching I see Oxygen 3 filters mentioned.

I would appreciate any suggestions .

Thanks
Mark

[Merlin66]

Hmmmm
With an 8" aperture, any filter will severely reduce the light throughput..
A OIII is usually recommended for Planetary neb, the Hbeta isn't worth the effort (visually).
Depending on your light pollution a multi-band LPR may be a better bet.

[Allan]

Hi Mark,

Just remember that when you put a filter in your eyepiece you're cutting down on the light you see, because that's the job of the filter. I'm not sure how well an OIII would work in an 8" because it is a 'line filter' which means it only lets a relatively small amount of light through, and in an 8" the image may appear too dark.

I think you should start off with a UHC filter. They still filter out some light, so the image will be a little darker, but not as much as the OIII so should work nicely in your 8". A UHC will really improve the contrast on nebula. After you have used one for a while you could consider an OIII then.

Don't bother with a Ha or Hb for visual use. Also I think the sky glow type of broadband filters are a waste of time as well. The UHC and OIII filters are definitely the workhorse filters for nebula use. I use both in my 12" and the Eta Carinae nebula viewed with my OIII blows me away every time.

[SkyWatch]

Hi Mark,
I find a UHC filter works really well, especially in the city.
O3 filters cut out a lot of the starlight so what you see is heavily biased towards emission nebulae- which is great if that is what you want; but the UHC filter allows more starlight through, so you get a more "natural" image, while still increasing the nebula contrast. I find the view much more pleasing. They work much better with galaxies too.
I go along with Allan: both are great (especially with Eta Carina!), but the UHC gets my vote as a good first pick.
- Dean

[MortonH]

Hi Mark,

I have an 8" f/5 Skywatcher and a Lumicon UHC filter. It is stunning on brighter objects like the Tarantula Nebula and pretty good on everything else. I had an OIII before but felt it was bit too dark in an 8" scope.

If you have bad light pollution a general LPR (light pollution reduction) filter might be better (and I have a 2" Lumicon Deep Sky filter that I don't use any more) but otherwise the UHC is probably the best bet.

Morton

[Nab]

I also have a 8" dob and after some extensive reading chose a UHC filter (I got the Astronomik UHC). My impression was (wow) how much darker it made the view, and the second the "wow factor" on bright nebula (Orion, eta-carinae, Tarantula, not so much on the crab). The UHC has also helped to spot some fainter nebula and planetaries that while being very feint through the filter were otherwise invisible. With some exceptions lower power and wide fields provide the best view.

I don't think you would want anything narrower otherwise the light attenuation will make the view frustrating.

Cheers.
Darren.

[dannat]

Try the DGM NPB Nebula filter, but if you re not at a dk sky I personally don't see much with a filter in at 8" of aperture

[Steffen]

This article (http://www.cloudynights.com/ubbthreads/attachments/652339-LPR%20Filters%20%2B%20Knisely.doc) discusses the use of filters for deep sky objects in some detail, worth a read IMO.

Cheers
Steffen.

[atman]

Thank you all for your generous replies, the advice has opened up my limited understanding.

So it would appear that a UHC filter would be the most useful for me at this stage.

The next 2 questions are

1. Should I be looking at getting a 2" or 1.25" filter?

My scope came with a 26mm 2" eyepiece which gives around 46x magnification.

The other 2 pieces are 1.25' (15mm and 9 mm). The 15mm ep gives 80x magnification.

And I guess the other issue is the width of field of view.

2. Which brand - it appears the costs are similar $250 for 2", $120 -$150 for the 1.25".

It appears the Astronomic is on a par with Lumicon ( but easier to get locally.)

There is another consideration is that I will most likely be upgrading eyepieces - as I become aware of the "need", and understand more - and intend to buy on quality rather than simply price.

The current scope I'll stay with until at least next year - mainly to try and max out its potential. Obviously any investments in eyepieces will be transferable to other scopes.

( Short term pain for long term gain - that's the line I'm rehearsing for swmbo.) Wife to Mark " You want to spend $250 on WHAT ????"

[Steffen]

The 1.25" eyepiece adapter that came with your scope most likely has a filter thread, so I'd go with 2" filters.

Cheers
Steffen.

[bytor666]

The UHC filter is not meant for viewing galaxies.

Cheers!

[Don Pensack]

Here is the low-down on filters.
Broadband filters--reduce wavelengths at which some lighting broadcasts. Makes the most difference in already-dark skies. Enhancement is minimal, kind of like turning up the contrast a tiny bit. Sometimes these are called light pollution reduction filters. Not really worth owning unless you already observe in dark skies and this would be your 4th choice. Good examples: Lumicon Deep-Sky, Orion Sky Glow filter, Thousand Oaks LP-1

Narrowband filters--Also called UHC filters, these filters pass the wavelengths at which emission nebulae emit: 486nm blue (Hydrogen Beta), 496nm blue green (Oxygen III) and 501nm blue green (O-III, 2nd line). This is the "universal filter" and transmits all the wavelengths from every nebula that emits brightly. You don't have to guess. Not effective on bluish reflection nebulae (these are full-spectrum and need darks skies, not filtration) or dark nebula (ditto previous comment). Good examples: Lumicon UHC, DGM NPB, Thgousand Oaks LP-2, Orion Ultrablock

Line filters-- represented by O-III filters (most effective on most planetary nebulae and certain emission nebulae) and H-Beta filters (work well when the primary emission is hydrogen, like IC434 behind the Horsehead nebula). These filters are specialty filters and create even more contrast enhancement for the objects they are best used for. Your 2nd choice filter (after a narrowband) would be an O-III, followed distantly by an H-Beta.
Good companies: Lumicon, Thousand Oaks, Orion.

The above information and David Knisely's article will tell you what you need to know.

[atman]

Thank you Don.

[atman]

I just found this thread on Cloudy Nights about filters.


http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5995047/page/0/view/collapsed/sb/5/o/all/fpart/1

[AstroJason]

Don't mean to hijack your thread Mark but been reading the links you have provided and there is some good info there so figure I will keep this going.

What are peoples thoughts on these two filters?

http://www.ebay.com.au/itm/Optical-Filter-501-Astronomy-OIII-Narrow-CCD-2-NEW-/150466319339?pt=Educational_Toys_US&hash=item23087dd3eb#ht_1115wt_1144

Anyone know if this OIII Line Filter is only designed to be used for imaging? Reason I ask is because it doesn't really mention visual use in the description but it mentions CCD use. Really want a good Line Filter.

Also...

http://www.ebay.com.au/itm/Filter-486-Astronomy-Hb-OIII-Nebula-II-48mm-2-/350238139324?pt=Educational_Toys_US&hash=item518bd1e3bc

Interested in this Narrowband filter that Alex (mental4astro) put me onto. Not really doubling up on filters am I?

[mental4astro]

Jason, the first one is a CCD filter - says so in the listing's title. CCD filters are are not intended for visual but optimised for an even tighter through pass & in a band width we can't see well if at all.

The second one you linked to is a visual filter. The Hb will help with spotting nebulae like the Horsehead neb, something normally only had in UHC type filters. It is a very good filter & represents great value for money.

Memtal

[Don Pensack]

The first filter is a CCD filter only, and centers on transmitting only the 501nm O-III line. For visual use, you will want one that also transmits the 496nm line.
Good brands to look for for visual use: Lumicon, Thousand Oaks, Orion
Too narrow for visual: Baader O-III, Celestron O-III
Too wide for visual use: TeleVue O-III, DGM O-III

The second filter is too wide to be considered a narrowband filter and too narrow to be considered a broadband. It isn't narrow enough to be very useful for visual observing of nebulae. You want the 486nm line of H-Beta and the 496nm and 501nm lines of O-III to come through, but very little else.
Good brands to look for:
DGM NPB, Lumicon UHC, Thousand Oaks LP-2, Orion Ultrablock
Too wide: Baader UHC-S, TeleVue Nebustar

[mental4astro]

The second filter is suggested as an OIII filter, not an UHC.

As an OIII filter it works.

I agree with Don's suggestions for UHC filters.

[AstroJason]

Wow, so much good info so quickly. Thanks Alex for pointing that out I figured that may have been the case and thanks Don for the info on the lines to look for too.

Don, is this the DGM NPB filter you mention? It has It seems to have additional peaks at 625 and 656. Is this too broad?

http://www.ebay.com.au/itm/NPB-2-0-DGM-Optics-Nebula-Astronomy-Filter-/310707955140?pt=LH_DefaultDomain_0&hash=item4857a325c4#ht_482wt_1399

[Don Pensack]

Alex,
The second filter says it is for Hb + O-III observing, which defines a UHC or narrowband filter. It does that, but with a little too much extra thrown in. It looks as broad as the Baader UHC-S.

Jason,
The NPB also has a transmission in the deep red. In really large scopes (say 400mm+), that translates to a better view of reds in nebulae. Some people like it, some don't. The Orion Ultrablock has literally no deep red transmission, so you won't see any reds at all. Fortunately, all nebulae transmitting H-alpha at 686nm also transmit H-beta at 486nm, and there our eyes are very sensitive.

[mental4astro]

Hmmm, Omega Optical apparently makes filters for other brands, big ticket brands. It could be that their OIII/Hb is one of those. After all, they have the capacity to produce their own premium in with their DGM line, a cut price 'home brand' just covers the lower end.

Either way, I'm happy with the performance of the OIII/Hb filter of theirs. Performs differently from the NPB I have, like an OIII would.

If premium prices are out of reach, or not important to one, the more modestly priced filters will still do a good job. You won't be looking into soup if that's what worries. But, I do think being properly informed is most important, regardless of one's ultimate choice. Picked up a couple of things too myself, :)

[Don Pensack]

The original narrowband filter, designed by Jack Marling of Lumicon, covered the H-beta and O-III lines emitted by gaseous nebulae with a bandwidth at FWHM (full-width, half maximum) of 23nm, approximately. The DGM NPB covers those wavelengths with a slightly narrower bandwidth. The purpose was to provide enhancement for nebulae while seriously darkening the background sky.

Marling also designed filters to cover just the H-Beta (about 9nm bandwidth) and just the O-III lines (about 12nm bandwidth), which he called H-Beta and O-III filters respectively. For study of those emission lines in certain nebulae. The O-III filter, specifically, was and is particularly successful at enhancing planetary nebulae.

An O-III filter can have up to about a 15nm bandwidth and still be considered an "O-III" filter, i.e. a filter that just passes the O-III lines in the spectrum and not much else, the goal being to enhance the contrast between the O-III emission lines and the background sky.

The link to the "O-III+Hb" filter shows a filter with about a 60nm FWHM bandwidth, which would not be considered an O-III filter by any company making them today. It wouldn't even be considered a narrowband filter (like Lumicon's UHC or DGM's NPB or Orion's Ultrablock) because the bandwidth is too wide.

At that bandwidth, it is similar to Baader's UHC-S, which sort of bridges the gap between a broadband filter (also known as a light pollution reduction filter) and a Narrowband filter (previously mentioned).

Since there are now a few filters with that wider bandwidth, we should probably refer to them as "wideband" filters to differentiate them from narrowband filters. They pass the O-III and H-Beta emission lines, for sure, but too much more to be considered a narrowband "nebula" filter.

I suspect they would do quite well when the sky is already really dark. And they wouldn't cause so many stars to disappear, which might be an aesthetically-chosen option.

The broadband, or LPR filter will have an even wider bandwidth, removing most of the deep yellow, orange, and shorter wavelength red, is made by many companies. The enhancement of nebulae is minor, sort of like turning up the contrast from 3 to 4 on a ten point scale. They work decently for photography and can be a "guilty pleasure" at a really dark site by turning up the contrast a bit without sacrificing all the stars in the field.

There are about 40 brands of filters out there now, and while the "wideband" filter could definitely be in the arsenal of nebula filters (especially for very small apertures), its reduced utility as a "nebula filter" would prompt me to suggest a narrowband as every observer's first nebula filter. There are many good ones (I've mentioned a few), but the one in the link is not one.

[glend]

Thanks folks and especially Don P for that very complete review. I've been lurking in the background on this thread while I researched my first filter for visual observing with my 12" dob, and I checked out the cloudynights link and noticed this comment:

David K's review of the DGM NPB filter showed that he was getting better contrast consistently with this filter over the Lumicon UHC. He then goes on to say, "The DGM Optics NPB Filter is an excellent narrow-band nebula filter which I recommend that nearly every amateur have in their eyepiece box."

Good enough for me, I've bought one.

[bytor666]

Hmmm, Omega Optical apparently makes filters for other brands, big ticket brands. It could be that their OIII/Hb is one of those. After all, they have the capacity to produce their own premium in with their DGM line, a cut price 'home brand' just covers the lower end.

Either way, I'm happy with the performance of the OIII/Hb filter of theirs. Performs differently from the NPB I have, like an OIII would.

If premium prices are out of reach, or not important to one, the more modestly priced filters will still do a good job. You won't be looking into soup if that's what worries. But, I do think being properly informed is most important, regardless of one's ultimate choice. Picked up a couple of things too myself.

[bytor666]

Alex,

A friend and myself did a shootout between the Omega / DGM O-III and an Orion Ultrablock and there was no difference at all !!! :eyepop:

[knightrider]

Has anyone had any experience on Prostar filters.
I've tried finding reviews or manufacturing information but can't find anything on them. From what I see they rebrand various products but try and provide value for money.

I was looking at their narrowband filter here: http://www.myastroshop.com.au/products/details.asp?id=MAS-001B3

Opinions? The only information I find is their own filter guide.

[JJDOBBER79]

I also bought the DGM NBP in the 1.25" for use with my 6" dob. My limited understanding is that this filter will become more useful as aperture increases. On the 6" I can notice a very slight contrast improvement on nebula, but not a whole lot. Thinking of upgrading aperture soon so hopefully will get more use out of it.

[GrahamL]

I've owned a lumicon uhc , orion ultrablock and now a DGM NBP
I find the dgm very differant to the other two both the lumicon and orion did a good job on enhancing different nebula, the dgm seems quite different in that it doesn't seem to throw up such the stark view and detail of the other two, anyone experience anything similar?

[mental4astro]

Last Sunday night I was finally able to do a side by side comparison of each of my three 2” filters. These are an Omega Optical Hb, a DGM NPB, and the Omega Optical OIII + Hb filter I mentioned earlier in this thread. The test target was the Horsehead nebula - if any nebula was going to sort the men from the boys it was this one. The scope used was my 17.5" dob.

The view through the Hb filter was the darkest. As to be expected as it is the narrowest band filter of the three. Seeing the Horsehead pillar was an exercise in seeing black on black. The glow of the background gas the pillar sits on is only just slightly brighter than the rest of the field. Once you knew where to look for the pillar it was quite striking, but by no means ripping your eyeball out obvious.

Next used was the NPB filter. Slightly wider band through put, so the whole field was a brighter, and so to spot the Horsehead, I’d say a little less contrast too. Yet, it was visible, and made easier knowing where to look.

Last was the OIII + Hb. I nearly didn’t use it thinking of Don’s words, but I thought ‘what the heck – let’s have a shot’. Well, the field again is slightly brighter than that of the NPB, and a lot more stars were visible, but, more importantly, the Horsehead WAS VISIBLE! And just as easy to spot as in the NPB!

Now, these observations were are not just my own. Jason, Steffen (who have added their voices to this thread) and Ed were there with me at Katoomba Airfield, and all looked through each of these filters. Now armed with verified practical experience on the OIII + Hb filter, and can most whole heartedly recommend it as a bloody good filter. Not theoretical scoffing at the labelled capability of the filter, but actual visual experience. It does as it claims. Interesting that no one has actually put down their experiences with this filter, but felt justified to dismiss it outright.

My hat off to Omega Optical in producing such a capable filter, AND at such an affordable price.

NB: Katoomba Airfield is 100km west of Sydney’s CBD at 1000m above sea level. Skies, while not text book perfect due to the proximity to Sydney, still provides excellent conditions due to its elevation. It certainly is good enough to allow us to see the Horsehead pillar without any major problem.

Mental.

PS: Don, your suggestion that the OIII +Hb filter would show more stars was very much correct. What is interesting is that while it may not strictly be a narrow band filter, it performed like one.

Mark, yep, I'd have to agree with your friends about the performance compariso, though I did find a slight difference, & I find the OIII +Hb visually more appealing.

[glend]

I have a DGM NPB filter that I use with my new 16" dob and I love the detail that it brings to life in nebula like Orion and Tarantula - at a truely dark site like Bretti. I have used it at home but feel to really work well it has to be used under very dark skies.

[gaa_ian]

This may be of interest for those looking for either a 1.25" or 2" UHC
I have found these UHC filters (http://everythingastronomy.com/buy-astronomy-products/)quite effective on increasing the contrast and extent of nebulosity visible at least on the Orion Nebula through an 8" Dob.
There is a link to the bandpass specs with the filter listing.
And yes (in the interests of disclosure) I am selling these filters, which are the same spec as those sold by "Orion"