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Old 10-01-2021, 12:27 PM
a5tarman
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UHC and OIII filters

Hi all, I primarily use my 10 inch dob under bortle 6/7 skies. I'm trying to understand if adding a UHC or OIII filter is worthwhile in my area. I'm hoping to add more nebulae to my observation list without driving to a dark sky site. What kind of effect could I expect. Will a filter simply make a nebula kinda sorta just barely visible with averted vision if I squint in a certain way, or can I expect more?
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Old 10-01-2021, 01:59 PM
ab1963 (Andrew)
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I have tried all the fancy filters and there is only one IMHO worth having and that's a Lumicon Oiii filter which i have in one of the older 1.25 versions as i only ever looked at nebula through the Docter 12.5mm but now i have the full set of Vixen SSW's will be doing the same with them so my advice is if you only have one filter make it Oiii
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Old 10-01-2021, 04:29 PM
astro744
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You will see a significant contrast boost especially with a narrower bandpass line filter such as an O-III under polluted skies. The UHC is a good choice as it passes O-III and H-Beta but given your sky pollution I recommend the O-III for greater contrast. The O-III is best all round line filter for most nebulae.

I also recommend the Lumicon O-III but you cannot go wrong with Astronomik or Tele Vue. Thousand Oaks is good too but transmission is a little lower at least on the sample I have so I think it is better on a larger aperture telescope (background is jet black though in 10.1” giving very high contrast!). I have all of these but the earlier Tele Vue not the latest Astronomik version. I do like the very natural look of the earlier Tele Vue O-III but my preference for a pure O-III line filter is for the Lumicon O-III. (My filters are about 8-10 years old). My recommendation is based on use of the above through various telescopes but mainly a 10.1” f6.4 Newtonian. I understand the new Lumicon O-III Gen 3 and newer Tele Vue (Astronomik) filters are very good based on reviews online but until I get these I cannot comment further.

See https://agenaastro.com/articles/guid...n-filters.html

See also https://www.televue.com/engine/TV3b_page.asp?id=24 and https://www.televue.com/engine/TV3b_...d=24&Tab=_spec

See also https://farpointastro.com/?s=O-III&p...ct&dgwt_wcas=1

See also http://thousandoaksoptical.com/products/nebula/

I’m not sure what eyepieces you have but you can start with a 1.25” version to test under your conditions and then later get the 2” version if you like it. Both are useful. Some users will suggest you get only the 2” version and a 2”-1.25” threaded adaptor; I won’t recommend this and neither does Tele Vue and that is why their adapters are not threaded. Reason being one day you’ll forget there’s a filter in your adaptor and put a 1.25” Barlow straight through it. Use the filter size to match the eyepiece barrel size. I bought 1.25” filters of various makes and types and then bought 2” versions of the ones I liked most.
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Old 10-01-2021, 05:20 PM
Startrek (Martin)
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I use the Astronomik UHC filter with my Televue Ethos and Delos eye pieces when observing nebulae under Bortle 3 skies with my 12” Goto dob. The UHC filter definitely exposes the nebulosity with more contrast and colour
I don’t know whether you would have the same performance under Bortle 6/7 but I’m sure it would make a significant difference
Cheers
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Old 11-01-2021, 08:01 AM
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Recommended:
Astronomik UHC visual
TeleVue BandMate II Nebustar
Lumicon UHC Gen.3
DGM NPB
ICS UHC

Recommended only if you can test the individual filter:
Orion UltraBlock
Thousand Oaks LP-2


Nebulae emit light in discrete wavelengths and any other light passing the filter is extraneous to seeing the nebula.

The more of the extraneous light suppressed, the darker the background behind the nebula and the more contrast there is between nebula and sky.

To achieve that, a bandwidth in the filter that just passes the light of the nebula is ideal.



But there are always slight irregularities in the production of filters, and they react differently to short f/ratios like f/4 or faster, so the bandwidth needs to be about 8nm wider than the minimum possible bandwidth of 14.6nm (the spacing between the H-ß line and the O-III lines)

So a 23nm filter would be the ideal.

Most of today's higher-quality UHC type narrowband filters are in the 22-27nm bandwidth range, like Astronomik, TeleVue, DGM, Lumicon, ICS.

45-50nm is very common among the Chinese UHC-type filters, so you want to avoid these if you can.

So since only 22-23nm of bandwidth is necessary for maximum contrast, the extra bandwidth just lets a bit too much light pollution through (why it only works best in a truly dark sky).

There is a little contrast enhancement, just not enough to make a large difference.



So, what can you do to maximize the experience?

1. Use only low powers with the filter. On an 10" scope, a maximum of 100x.

2. Make sure you are as dark-adapted as possible. That means 30-45 minutes outside, away from all lights, i.e. at least 30 minutes after turning off all lights.

3. Make sure the object you're looking at is at least 30° above the horizon. Your nebula target would lose ~0.25-0.3 magnitudes of brightness at the zenith, and double that at 30°.

It could lose a whopping 2.5-3.0 magnitudes at the horizon!! So try to view the nebula when it is near or crossing the imaginary N-S meridian.

4. Make sure the nebula is an emission-type nebula. The nebula filters won't help reflection nebulae like those in the Pleaides or M78 in Orion.

5. The 2" size is more universal--it fits 2" eyepieces, the bottom of most 2" to 1.25" adapters, and 2" star diagonals in compound scopes.
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Old 11-01-2021, 09:13 AM
a5tarman
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Thanks guys. If I were to only have one filter, UHC or OIII? Ideally I'd be driving to dark sky sites but with 90% of my observations under sky pollution I'd like to make the most of it.
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Old 11-01-2021, 11:03 AM
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A UHC filter passes both the H-ß line in the spectrum and the O-III lines.
If you KNOW what spectral lines are emitted by the object, a separate H-ß or O-III filter would be narrower and provide better contrast.
But if you don't know, the "universal" nebula filter is the narrowband UHC-type.
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Old 11-01-2021, 02:04 PM
ab1963 (Andrew)
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Quote:
Originally Posted by a5tarman View Post
Thanks guys. If I were to only have one filter, UHC or OIII? Ideally I'd be driving to dark sky sites but with 90% of my observations under sky pollution I'd like to make the most of it.
Why I highly rate the older Lumicon oiii over even the Astronomik is that with all UHC or Oiii filters I’ve ever used there’s always a green or blue colour cast but the 1.25 Lumicon Oiii 1.25 I have keeps the stars pretty much white and that was a big thing for me and the reason I got rid of everything else I had as nothing else i have used has matched this filter no fancy statistics just screwing the filters on eyepieces and having a look
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Old 11-01-2021, 03:11 PM
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gaseous (Patrick)
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That's interesting Andrew, the new Lumicon OIII certainly presents a definite green tinge to my eyes (as has every other OIII I've ever tried). The DGM NPB tends to give things a slight russet tinge, but not as "in your face" as the OIII green. The DGM NPB used to be my go-to filter, but I'm tending towards the Lumicon more recently as it tends to provide a bit more contrast to my eyes. I've never used a narrowband or line filter that kept the stars white, that would be a godsend.
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Old 11-01-2021, 04:16 PM
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Quote:
Originally Posted by gaseous View Post
That's interesting Andrew, the new Lumicon OIII certainly presents a definite green tinge to my eyes (as has every other OIII I've ever tried). The DGM NPB tends to give things a slight russet tinge, but not as "in your face" as the OIII green. The DGM NPB used to be my go-to filter, but I'm tending towards the Lumicon more recently as it tends to provide a bit more contrast to my eyes. I've never used a narrowband or line filter that kept the stars white, that would be a godsend.
That would be impossible if it is working.
The lines in the spectrum emitted by nebulae that we can see are blue and blue-green.
Some nebula filters pass some red as well, but that still doesn't make white stars white. If they are, the filter isn't filtering properly.
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Old 11-01-2021, 05:03 PM
ab1963 (Andrew)
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Quote:
Originally Posted by Don Pensack View Post
That would be impossible if it is working.
The lines in the spectrum emitted by nebulae that we can see are blue and blue-green.
Some nebula filters pass some red as well, but that still doesn't make white stars white. If they are, the filter isn't filtering properly.
Well all i can go by is what i see and that's candy floss nebula with very slight coloring in the stars it's not always about statistics this and that and i have a filter that performs this way i will send it to Rainmaker only as proof to verify and will throw all your stats in the rubbish bin
i do not lie i only judge by my senses, It's no different to the flogging the Vixen SSW's have had from some people i was out last night using them in a FSQ106 if you think that is a worthy Apo and from 3.5mm to 14mm an absolute joy to use even in my Pentax spotter perfect so now i don't listen to other peoples views on astronomy gear just look and make my own conclusions......

Last edited by ab1963; 11-01-2021 at 05:18 PM.
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Old 11-01-2021, 06:25 PM
astro744
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I think what Don said about it being impossible was a filter that produced white stars and not referring to what you see.

When Tele Vue first introduced their original Bandmate Nebustar (UHC equivalent) they made a point of showing how their filter didn’t produce red/blue fringing around stars like a competitors filter did. I have seen this in a filter and I much prefer the Tele Vue solution which gave mildly green stars of uniform colour.

I think the Astronomik filter (8+ years old) shows red/blue fringing and I’ll check next time I’m observing. (It’s either Astronomik or Lumicon but i’m fairly sure it’s the former and Tele Vue didn’t name which competitor it was). The original Tele Vue Nebustar is fairly gentle compared to the UHC from Astronomik, Lumicon, Thousand Oaks but gives much better contrast than say a Lumicon Deep Sky filter. I much prefer the original Tele Vue Bandmate O-III filter which provides a nice presentation offering good contrast and more stars albeit with a mildly green tinge. Many put down the original Tele Vue Bandmate O-III saying that the bandpass was too wide and not quite centred on the double Oxygen lines but I wonder how many of those commenting have actually used the filter and not just looked at the bandpass curves.

It is interesting that Tele Vue now paired with Astronomik to produce the Type 2 Bandmates which to my understanding have tighter and more accurate bandpass with high transmission and significant quality control. My take is that Astronomik improved their own filters and teamed with Tele Vue to offer a superior product to what either had before. I’m not sure if the red/blue fringing was addressed and when I get some spare funds I’ll invest in the newer Bandmate Type 2 Nebustar to see for myself through the eyepiece and not have to rely on interpretations of curve data.

Note contrary to what many believe UHC & line filters work best under dark skies but of course perform well under light pollution. Exit pupil too and telescope aperture determine how each filter behaves and sometimes it is only by experimentation that you find the best solution.

When Lumicon first marketed these filters in the 1980s (I can remember seeing the ads) the UHC was the recommended filter. The O-III was available to those seeking to find elusive planetary nebulae whilst the H-Beta was simply called the Horsehead nebula filter. Note the UHC includes both O-III and H-Beta but to have any chance of seeing the Horsehead you need the narrow band pass of the H-Beta filter alone. I believe that under heavy light pollution the narrower bandpass of the O-III would serve you better but the UHC would still provide a significant contrast boost.
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Old 12-01-2021, 01:02 AM
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When a star is too faint to activate cones in the retina, it will appear colorless, which the brain interprets as white or gray.
Bright stars, however, will activate cones and you will see colors, as we do with Betelgeuse or Antares, etc.

When a filter passes only the blue-green, as with the TeleVue BandMate II Nebustar or Lumicon UHC Gen.3, if a star is bright enough to activate cones, it will appear blue-green if any color is seen at all.

The Astronomik UHC visual also passes a broad swath of red, so some red flaring will occur when looking at a star if the star is bright enough.
The DGM NPB passes the red, but includes some shorter wavelength orange, so if color is seen in the stars, the stars appear red orange because the majority of light passed by the filter is in the red-orange with only a narrow sliver in the blue-green. The DGM NPB has about the narrowest bandwidth in the blue green available in UHC-type filters today, at around 22nm.

Older TeleVues (pre 2018) were wider, as were older Astronomiks (pre 2016), but you have to go back to pre-2001 to see any red in Lumicon UHCs.

I've used all of these extensively on nebulae over the last 3 years, as well as 48 other nebula filters.

Where O-III filters are concerned, the TeleVue and Astronomik are now pretty much identical, as is the ICS filter. They are all made by Astronomik. The Lumicon is made in the US, but has a nearly identical bandpass to the others.

The DGM is wider and doesn't offer the contrast of those others. Baader and Thousand Oaks are single-line O-III filters and more appropriate to imaging.

As is the case with the UHC-type filters (where 45-50nm bandwidths predominate), most of the Chinese O-III filters are very wide, with bandwidths of 25-28nm quite common. Had their bandwidths been placed differently in the spectrum, they'd have been high-end UHC-type filters, but their bandpasses miss the H-ß line.

With the bandpasses common in the better UHC-type and O-III filters today, the contrast enhancement of the UHC-type filters runs about 2.5 magnitudes, with the narrower O-III filters yielding about 3 magnitudes.
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Old 16-01-2021, 09:41 AM
morls (Stephen)
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I wonder what opinions are regarding the Baader 6.5nm OIII, Ha and SII?


Also, where do Optolong sit in the mix? As I understand things they initially had issues with haloing, but later production seems to have remedied this?
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Old 16-01-2021, 11:31 AM
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I wonder what opinions are regarding the Baader 6.5nm OIII, Ha and SII?


Also, where do Optolong sit in the mix? As I understand things they initially had issues with haloing, but later production seems to have remedied this?
All are imaging filters.
The Baader 6.5nm O-III is a single line O-III filter, wider, but less expensive, than the very high end imaging filters.
They also make an H-α and S-II filter for imaging. Very cost-effective for what they are and do.

Optolong's L-Enhance is basically a UHC filter with a peak at H-α.
Their L-Extreme is basically an O-III with an H-α peak.
You can find reviews of both on line.
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Old 16-02-2021, 02:18 AM
mandragara (Richard)
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What do you guys think of the Baader O-III filter?
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Old 16-02-2021, 04:00 AM
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What do you guys think of the Baader O-III filter?
The Baader O-III filter is an inexpensive photographic O-III filter.
It passes only one of the two O-III lines, so reduces the size and brightness of the O-III features from what our visual system needs.

I would recommend an O-III filter that passes both O-III lines at a high percentage, like Astronomik O-III or Lumicon O-III Gen.3 or TeleVue Bandmate II O-III or ICS O-III.

There could be a place for a single line O-III filter if you are investigating particular features in an O-III emission object, but be aware the field and object will be darker. It would be a second O-III filter, though, after you have purchased a dual line O-III filter for primary visual use.
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Old 16-02-2021, 10:10 AM
mandragara (Richard)
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Cheers!

I realised I made a rookie mistake of buying the narrow Baader OIII filter - I thought narrower = better as less light pollution creeps in, but now I see I'm probably losing out on some light with this O-III filter (I bought it to better highlight planetary nebula).

I guess I should try and sell it and get a better visual filter - it's a shame as I paid almost as much for it as the cost of an Astronomik OIII filter, oh well call it a learning experience
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Old 25-03-2021, 03:52 PM
mandragara (Richard)
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Just a follow up. Got my hands on an Astronomik O-III and the views are better than through the Baader O-III. So for anyone stumbling across this thread, that's the choice to make for visual
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Old 25-03-2021, 11:49 PM
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Yes, the Astronomik O-III is a 2-line filter which passes the 495.9 and 500.7nm lines at a high %, where the Baader O-III is a 1-line filter that only passes the 500.7nm line and at a slightly lower % transmission.
The Baader is a decent filter for imaging, but it cuts too much light for the best visual image.
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