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Can filters help visual observing?

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#1 ChemguyLenny

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Posted 19 October 2018 - 09:15 AM

I am wondering if it is worth getting some of these specific filters (nebular, narrow band, etc) vs the regular filters RGB, etc. if I am just doing visual observing - no photography?  I have a 120ST, a 6SE, an Orion 8 inch dob and an older (nice) Celestron 80.  I can see the little fuzzies and the Orion constellation nebulas are visible.  Would special filters make my viewing more special?  Thanks.



#2 arnaud_dupuis

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Posted 19 October 2018 - 09:29 AM

Hi,

 

TL;DR: Yes absolutely.

 

You should first have a look at these articles:

 * https://www.prairiea...common-nebulae/

 * https://www.prairiea...ep-sky-objects/

 

Basically a UHC/Narrowband and OIII filters are a must for nebulae observations. They make it pop a lot more.

The veil, dumbbell or ring nebulae all benefit from OIII filter (a lot) for example. Orion is more of a narrowband nebula. 

 

One point I have read many time is that you need a minimal aperture for at least OIII filter (6 inches if I remember correctly). I cannot tell you on that, I only have a 10 inches dob. Others might be able to help you on that point.

 

Anyway, it's a bit of an investment (particularly if like me you have 2 inches and 1.25 inch eyepieces, it can quickly add up to 500$) but it's really worth it. In light polluted AND dark skies environments. 



#3 dcollier

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Posted 19 October 2018 - 09:34 AM

I would also consider the Baader Moon and Skyglow filter.  I works well for planetary Mars, Jupiter, Saturn and makes galaxies more visible in light pollution.  It is not magic though.. 


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#4 petert913

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Posted 19 October 2018 - 10:11 AM

My experience with DSO's  is that filters work very well for larger aperture scopes.   10" and above.  Smaller optics just seem to give a

darkened view of the object.



#5 quazy4quasars

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Posted 19 October 2018 - 10:18 AM

  The best filter is a tankful of gasoline.

 

  I use a UHC and an 0III  from time to time, but observing from dark sites, it's rare I really feel like it's necessary.  


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#6 wrnchhead

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Posted 19 October 2018 - 10:22 AM

No purporting to be an expert, but I picked up one of the cheap Svbony filters, and with my 8" in town and out in the dark sites it made a noticeable improvement visually. Sure, cheap may make you wish you had saved your money for a better one, but I am not unhappy with my purchase. 


Edited by wrnchhead, 19 October 2018 - 10:23 AM.

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#7 Jeff Struve

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Posted 19 October 2018 - 10:23 AM

I have a number of filters... I don't find any of the planetary filters valuable. An LP and an Oiii and an UHC seem ok, but for the most part, to me, they do improve the contrast but dim things too much for my liking.

 

I do find a moon filter or variable polarizer valuable for dimming the moon... and a solar filter of course, but that's about it.



#8 Waddensky

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Posted 19 October 2018 - 10:24 AM

Yes, a good narrowband filter will bring out detail and improve contrast in visual observations of emmission nebulae like planetary nebulae. They don't make the nebula brighter, but they darken the background. The effect is really remarkable. I'd recommend reading the links Arnaud provided to get an idea of the effect. A good narrowband filter (sometimes marketed as 'UHC'), like the Lumicon UHC or the DGM Optics NPB, is a great start. Line filters like OIII or H-beta are perhaps nice upgrades when you know what filters do and are looking for a decent view of some specific nebulae.

 

Remember that these filters are not suitable to observe galaxies and reflection nebulae.


Edited by Waddensky, 19 October 2018 - 10:29 AM.

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#9 havasman

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Posted 19 October 2018 - 11:46 AM

+1 for the OP reading Knisely's Prairie Astro articles suggested in post #2 to gain basic info on visual filters principles and use.

 

It is critical to define visual versus imaging filters. The RGB filters referenced are imaging filters and not much use for visual astronomy. Visual filters work to dim every energy band EXCEPT the filter's passband. Choosing a filter with a passband matched to a nebula's emission band can greatly increase the apparent contrast of the nebula against the darker, filtered background.

 

I have observed with narrowband and wideband filters with scopes from 4.5" to 32" apertures and have found narrowband filters universally effective in all those scopes from dark sites and from very poor urban observing locations. I have also found wideband filters almost completely ineffective for my purposes. I have installed narrowband filters over the objectives of 10x50 binoculars and come to the same conclusions as for scopes.

 

Filters I have and use successfully include Lumicon UHC and Gen3 O-III, Thousand Oaks O-III and H-Beta and DGM NPB filters. They are all narrow-to-very-narrow passband filters.

 

Filters I have tried and found ineffective for my uses are Celestron UHC/LPR, Starguy UHC and Baader UHC-S. Those are all wideband filters.

 

_______________________________________

edit:

Galaxies, stars, and star clusters are all full range broadband emitters. As much of their available light energy is filtered as is removed from the rest of the field. So contrast is not enhanced. The same is true of reflection nebulae though they do not emit. They reflect relatively full range energy from broadband emitters and so are filtered also at the same rate as their backgrounds. Again, contrast is not enhanced. Some nebulae with both emission and reflection components can be enhanced but the effect is limited to the emission components. I think all this is likely in the Knisely articles.


Edited by havasman, 19 October 2018 - 03:16 PM.

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#10 stoest

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Posted 19 October 2018 - 01:28 PM

I consider my DGM NPB filter an essential part of my kit and I don't believe an observing night goes by without me getting very good use from it. On both of my scopes it brings out details and makes things visible to me that I couldn't see without the filter.  If I lost or broke my filter I would order a new one today, it's that important to my visual observing.  I'm a 100% visual observer.


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#11 Tony Flanders

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Posted 19 October 2018 - 01:51 PM

One point I have read many time is that you need a minimal aperture for at least OIII filter (6 inches if I remember correctly). I cannot tell you on that, I only have a 10 inches dob.

My buddy Josh Roth routinely uses an O-III filter on his 50-mm refractor, both under dark skies and in light-polluted skies. It allows him to spot the Veil Nebula from his suburban back yard.

I routinely use both an O-III and a UHC filter on my 70-mm refractor, and again I find them immensely helpful.

The bottom line with nebula filters is that they make a huge difference on a relatively small number of objects. No filter helps much, if at all, for observing star clusters and galaxies.


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#12 Redbetter

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Posted 19 October 2018 - 05:52 PM

My experience with DSO's  is that filters work very well for larger aperture scopes.   10" and above.  Smaller optics just seem to give a

darkened view of the object.

That indicates you aren't using them properly or at least not on the correct targets for the aperture.  The observed surface brightness of the object is due to the exit pupil employed.  If you observe at the same magnification with a smaller aperture the object will indeed be dimmer.  If you instead use a large exit pupil and low magnification you will see a smaller, brighter object.  The California nebula is surprisingly small but relatively bright in a 60ED with a 41 Pan and 2" H-beta.

 

I use apertures from 50mm to 20" with filters.   The larger the object the smaller the aperture/wider the true field of view.   I formerly used an old 1.25" O-III in my 50mm finder for things like the Rosette nebula.  I use a 60ED scope with 2" H-beta for Barnard's Loop with large exit pupil, and have also used the 80ED and 110ED for this.  Similarly the Veil and North America nebula are a treat in small apertures.  Refractors with 2" focusers excel for wide field nebula viewing.   Each scale has its own advantages, so I have also explored even Barnard's Loop with the 20", again with large exit pupils.


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#13 Roragi

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Posted 20 October 2018 - 07:34 AM

As you have already said, if you do not have any, the first one to have is an UHC type, the next an OIII.


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#14 kfiscus

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Posted 20 October 2018 - 09:50 PM

You owe it to yourself to try a DGM NPB (Narrow-Pass Band) under dark skies and with dark-adapted eyes. You will see new features in old favorites and you will be able to find objects that eluded you before.

Edited by kfiscus, 20 October 2018 - 09:51 PM.

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#15 Feidb

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Posted 21 October 2018 - 08:17 AM

Filters can be great visual aids under almost any skies.

 

In order, I've found the UHC, O-III and H-Beta the most useful.

 

I use all three in the field, lately the O-III more now because I'm no a quest for planetaries as one of my observing goals.


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#16 wrnchhead

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Posted 21 October 2018 - 08:23 AM

Used my Svbony this morning in the city and made a nice difference on Orion. 



#17 Dave Mitsky

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Posted 21 October 2018 - 10:05 PM

Narrowband and OIII filters can make a world of difference in some cases.  NGC 1514 (the Crystal Ball Nebula) is a good example.

 

https://observing.sk...c/NGC_1514.html

 

B33 (the Horsehead Nebula) is often extremely difficult to impossible to see without the aid of an H-beta filter.

 

https://www.skyhound...jan/IC_434.html

 

A narrowband or OIII filter is very useful on NGC 2359 (Thor's Helmet), NGC 7293 (the Helix Nebula), the Veil Nebula complex, and many other nebulae.

 

Dave Mitsky


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#18 ChemguyLenny

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Posted 21 October 2018 - 10:50 PM

I have noticed when looking at the different filters uhc, oiii, etc. they mention that these are meant for 8 inch scopes or greater. What is good for a 120st or 6SE? Anything good for a celestron 80 refractor made in Japan?

#19 Redbetter

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Posted 21 October 2018 - 11:47 PM

Ignore the aperture claims/restrictions for the most part.  What matters is the surface brightness of the nebula and the exit pupil used.  With a smaller scope one will typically be targeting larger or brighter nebula with the filters.  If you try to use small exit pupil/high magnification with narrow or line filters then you will indeed get a very dim view.    But large exit pupils still work with small aperture, just as they do with medium or large aperture.  The 120ST should be excellent on large nebula targets with such filters using wide true fields and large exit pupils. 

 

The trade off to maintain image brightness is scale.  You can't expect to use the same magnification effectively with smaller apertures as for medium/larger apertures for nebula, with or without filters.  There are some planetary nebula, etc. that have high surface brightness and will respond well even with high magnification, but there are many nebulae that do not.  The filter will still decrease the background glow and accentuate emission nebulae, but the scale could be problematic. 

 

If you don't have appropriate eyepieces to match with a filter to achieve sufficient exit pupil, then you will likely find it more difficult to employ a narrow/line filter with small aperture except on a few targets.  The 6SE at f/10 is more challenging in this regard since one might only be using 1.25" eyepieces and might only have a 32 Plossl or 24 Pan for the low mag/moderate exit pupil end.  I don't know about the 80mm as I have no idea what ratio it is or what focuser it has.


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#20 Spartinix

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Posted 22 October 2018 - 01:39 PM

I've only got back into observing three years ago, after living in a light-polluted country for 20 years. I never used filters in the four years in my youth, observing from dark skies, with my 8" F4.

 

A year ago, a good friend of mine recommended me one day to invest in a UHC filter before trying out another eyepiece. I didn't feel like spending $200 on a filter but I followed his advice. Observing from good skies (21.3-21.8) I was curious to see what might improve.

Meanwhile I'm using an OIII as well, and I looooove switching filters and comparing views. I love it so much I made an 8-slot filter wheel on the inside of my tube so I can switch fast and easily soon. I'll be adding a Televue Bandmate Nebustar (no red), an H-Beta and a few color filters for solar system observing.

 

I don't share the sentiment of some saying there's no need for filters under dark skies. Sure, I will always observe whatever object without filters as well, but I like both. 

 

Just two days ago, I spent over half an hour admiring the UHC-filtered Rosette nebula at 79x, in a 62 arcminute-field and an exit pupil of 6.2mm, in the 19.5".

I like looking filtered with my 6" scope as well, as mentioned, at large exit pupils. In my main scope, I observe filtered also up to ~220x of magnification for now.


Edited by Spartinix, 22 October 2018 - 01:44 PM.

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#21 Starman1

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Posted 23 October 2018 - 11:41 PM

We seem to have a new thread asking exactly the same questions about filters every two days.

Here is a good synopsis of what they do as posted a few days ago:

https://www.cloudyni...-uhc/?p=8906084

Pretty much sums it up.


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#22 REC

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Posted 27 October 2018 - 09:56 AM

I consider my DGM NPB filter an essential part of my kit and I don't believe an observing night goes by without me getting very good use from it. On both of my scopes it brings out details and makes things visible to me that I couldn't see without the filter.  If I lost or broke my filter I would order a new one today, it's that important to my visual observing.  I'm a 100% visual observer.

+1 on the NPB filter.




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