Filter to view nebulae

[atman (Mark)]

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 (Ken)]

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 (Dean)]

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 (Darren)]

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 (Daniel)]

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 discusses the use of filters for deep sky objects in some detail, worth a read IMO.

Cheers
Steffen.

[atman (Mark)]

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]

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

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 (Mark)]

Thank you Don.

[atman (Mark)]

I just found this thread on Cloudy Nights about filters.


http://www.cloudynights.com/ubbthrea.../o/all/fpart/1

[AstroJason (Jason)]

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-F...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-48...item518bd1e3bc

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

[mental4astro (Alexander)]

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 (Alexander)]

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 (Jason)]

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-D...#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.