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Which first best nebula filter?


View2

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Torn between which 2" filter would best suit my scope for things like dumbell and cygnus loop. I have a moon filter coming already as the moon is blinding.

The scope is a 127mm apochromatic ED triplet refractor, f/7.5 (fl=952mm). Although not f/10, it should still have high contrast(obviously I have not had it out yet). Have 2" Meade UWF EPS and some other 1-1/4 EPs). 

Am hesitating to get the UHC filter over an OIII. Hoping for some input here, and perhaps recommend brand. I know the baader ones are supposed to be high end, but have heard they are not much if any better than a celestron O3? 

 

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I would check the actual transmission curves first, I have seen some "Nebula filters" that are just OIII filters in that they transmit the OIII but nothing up at the Ha end. OIII transmits just the OIII wavelength whereas the Nebula should (I think) pass OIII and Ha.

Have a look at this: http://www.astrosurf.com/buil/filters/curves.htm#Meade%20Nebular

Scroll to the Meade Nebula filter and the next is the TV one. Meade transmits OIII and Ha but TV transmits just OIII no Ha, both are Nebular filters but different transmitted wavelengths.

It was not on here but on CN where it was reported that Celestron buy their filters from Baader, so they tend to be very similar. Maybe not 100% identical but close.

Over on CN there was a post about filters, where the actual transmitted wavelengths were measured. Posted a couple of months back. Amazing how many did not have their peak transmission at the expected wavelength. That is worth tracking down and reading.

From the data the Astronomic UHC filter looks good for both wavelengths. For OIII only take a look and decide if you want to include or exclude the Hb wavelength.

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This question is a very common one. And there are no cut & dried answers. A coin is tossed in the air and called before it lands. UHC or OIII? It depends on which objects in particular you are wanting to look at first - assuming you can't afford both at first. As regards the best brand to get, I'd look at the spectrum that the filter allows to come through. A wider spectrum indicates it lets through more of the light emitted/reflected from the object, so a brighter view. Personally I like this 'more light' as most of my personal observations are done visually. For photographic work, many would opt for the more narrow-banded filter. Or not. The Baader-line is very well spoken of, so you can't really go wrong. So I wouldn't let this decision stress you.

Just do beware - filters can become a slippery-slope. Some people end up with getting filters of all description. I know - I have over 36 of the little critters! :D

Have fun! A certified Filter-Nut,

Dave

Singularity Filter.jpg

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The Celestron O-III is a re-branded Baader O-III. They have rather a narrow band-pass width (narrower than most other O-III's) which means that the background stars all but dissapear in smaller aperture scopes. I used to use an Astronomik O-III in my 4" and 4.7" refractors as well as my 12" dosbonian and that was a superb filter - almost a single DSO filter solution in fact.

Prior to that I used an Orion Ultrablock which is a good UHC type filter. That worked well in the smaller as well as the larger apertures too.

For the Veil Nebula (Cygnus loop), which is one of my favourite Summer objects in all my scopes, in my opinion a good O-III filter such as the Astronomik or my curreny Lumicon provides the best views of any filter by quite some distance. Absolutely wonderful on a dark night even with my 4" refractor :icon_biggrin:. Worth the price of the filter and the wide angle / low power eyepiece alone IMHO.

For other objects such as M42 and the Dumbell I tend to prefer the more subtle enhancement that a good UHC gives. Currently I use an Omega DGM NBP for this, which is really good on these objects.

If I was on a tighter budget and had to pick just a single DSO filter for a modertate aperture I think I'd go for either the Astronomik O-III or the less expensive Orion Ultrablock.

 

 

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I'm really not into the science or math of optics, and like the opening poster i was once torn between which nebula filter to buy first (UHC or OIII). I wanted to see as many as possible. I cant remember who said it to me, but it was a fellow member of SGL. They said:

"A UHC filter will enhance the nebulae already visible through a scope, while an OIII filter will make the invisible visible". No truer word ever spoken. I bought both. I bought the Skywatcher 1.25" filters and have no complaints.

The UHC enhances what you can already see in a scope (m42 etc) and the OIII allows you to see such beauty as the Rosette/Veil.

Haha......this is the 2nd time ive posted this comment today. People must be getting into Nebulae.

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To understand how thess filters work is by looking at their characteristics.

The main light spectrums for these filters are 486nm (H-beta), 496nm(OIII) and 501nm(OIII).

Hb filter: high transmission for 486nm, blocks the OIII lines(496nm and 501nm) totally.

OIII filter: high transmission for OIII lines, blocks the 486nm totally

UHC filter: high transmission for all H-beta and OIII lines, blocks spectrums outside these area.

The logical consequence of this is

1. Nebulas with strong light spectrum in 486nm, will benefit most with Hb filter, UHC works too with lesser contrast, while OIII will totally kill the nebulas, HH and Cocoon are examples.

2. Nebulas with strong light spectrums in 496nm and 501nm, will benefit most with OIII filter, UHC works too with lesser contrast, while Hb will totally kill the nebulas. The Veil is a good example.

3. Nebulas with strong light spectrums in both H-beta and OIII lines, UHC will show most extended nebulosity, while OIII and Hb will show very different partial nebulosity.

4. Nebulas without strong light spectrums in these area, none of these filters can be of any help.

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Thanks all!

 From what I've gleaned, I think I will enjoy the new scope naked until mid summer. I plan on going to larch mountain here locally to view. If memory serves there are almost always folks there viewing during friendly weather. There i should be able to compare filters doubt. I used to have an 8" sct but sold it about 15yr ago. Been having severe astro withdrawal symptoms  lately and now have a 5" f/7.5 refractor. Not a light bucket, but anticipating some nice views all the same. I don't plan on doing any astro photography off the bat, just viewing using an ioptron ieq45p.

BTW, what is "kit" and "frac"?

Cheers 

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Generally, Lumicon filters are considered the gold standard against which all other interference filters are judged.  I have their 2" O-III and find it to be much superior to a cheap 1.25" Zhumell O-III I picked up.  I also have the Lumicon 1.25" UHC, but prefer the O-III for the higher contrast on just about all nebulae.  There are quite a few threads on CN about various filters and their passband widths and percentages.  David Knisely is the local filter expert over there.

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  • 2 weeks later...
On 5/17/2016 at 23:22, View2 said:

Torn between which 2" filter would best suit my scope for things like dumbell and cygnus loop. I have a moon filter coming already as the moon is blinding.

The scope is a 127mm apochromatic ED triplet refractor, f/7.5 (fl=952mm). Although not f/10, it should still have high contrast(obviously I have not had it out yet). Have 2" Meade UWF EPS and some other 1-1/4 EPs). 

Am hesitating to get the UHC filter over an OIII. Hoping for some input here, and perhaps recommend brand. I know the baader ones are supposed to be high end, but have heard they are not much if any better than a celestron O3? 

 

Since the UHC narrowband filter transmits the H-Beta and O-III lines most nebulae emit, it would be your first choice for sure.

Different nebulae can have improved contrast with a separate O-III or H-Beta filter, but unless you know the spectrum of the object being viewed, a narrowband is the "universal" nebula filter.

The second filter you would purchase would be a line filter like the O-III.  There are a lot of nebulae most enhanced by the O-III, so it is a logical second choice.

Many people stop there.  There are a handful of objects for which the H-Beta filter is best (e.g. The Horsehead, the California Nebula, et.al), but it would be a fairly distant 3rd.

The narrowband filter can also be used on these objects.

The key is to get one with a narrow-enough bandwidth to yield good contrast.  All the UHC filters work, but the narrower ones provide the best contrast (and also the darkest image of the overall field).

The narrow ones emphasize the nebula over the stars and field brightness.  The wider ones emphasize stars and field brightness over the ultimate nebula enhancement.

If viewing from the city, I'd go narrow.  If viewing from a truly dark site, I'd say it's a toss-up which you would prefer.

Known to be narrow:

Lumicon UHC, Thousand Oaks LP-2, DGM NPB, Orion Ultrablock, Farpoint UHC.

The newest Astronomik is narrower than the older ones and might make it into this category now.

Know to be wide:

StarGuy UHC, Optolong UHC, TeleVue Nebustar, Explore Scientific UHC, Baader UHC-S, Celestron UHC

There are other filters in the market, but tests for them may not be easy to find.  So you can get some specs and evaluate for yourself, look for these:

>90% transmission at 486nm, 496nm and 501nm.

FWHM (full width half maximum) bandwidth of 23-28nm

optical glass

hard-coated (can be cleaned)

Hope that helps

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Very much so, thanks. Now need advice on a 35mm 2" EP.  Looking at the TV panoptic maybe, but heard of weird pincushion effects? Again, the Scope is an f/7.5 127mm apo with 952mm focal length.

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The big pans are great eyepieces but are large and heavy. You may need some counterweighting to help balance your scope when using them. The pincushion effect you speak of bothers some but not others, it's kinda a case of suck it and see ;) 
It's never bothered me when using panoptics. 

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If a 32mm or 38mm would work for a 2" with 70° FOV, I've found these far-less-costly eyepieces work quite well in fast, as well as slow, refractors:

http://www.universityoptics.com/2inch.html#WS70

They are threaded and I've had no problems screwing filters into them.

I was surprised they were this inexpensive - and worked so well -

Dave

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