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Filters that work for galaxies

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#1 Bill Steen

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Posted 11 February 2015 - 10:38 PM

I am finding, once the Moon went down, that the Meade HD 60 25 mm eyepiece I have has more clarity and light throughput than my ES 6824A.  I am wanting to use the HD 60 to locate galaxies that I have not been able to find before, using my modified Polaris 130.  Some of the galaxies I am looking for may just barely be visible, but I am not sure if I am really seeing something or if it is my imagination.  I am using all the observing tricks that I know about.  Even an 82A filter I have seems to help a little bit, but I really need a little more assistance.  I am not really trying to see any detail, just be able to say, "There it is!" with more confidence that I really am seeing an indication.

 

I was wondering which of the light pollution/moon glow filters or any other filters for that mater would be truly helpful with this endeavor.  Probably something in the $90 price range would be about top dollar that I would be willing to spend on a 1.25 inch filter at this time or in the near future.

 

With the additional light throughput, I should be able to give up a little light for the right filter and still have the brightness of the ES 6824, but with less light pollution and better contrast.

 

I am wondering about the Baader LP and Moon Glow Filter as one particular example.

 

Any and all thought, opinions, suggestions are appreciated.

 

Thanks,

 

Bill Steen



#2 Mariner@sg

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Posted 11 February 2015 - 11:22 PM

I'd say the gas filter is the best bet.



#3 David Knisely

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Posted 11 February 2015 - 11:36 PM

The only kind of filters that help galaxies at all are the so-called broadband "LPR" type filters (Orion Skyglow, Lumicon DeepSky, IDAS LPS filter, DGM Optics GCE, etc.), but the enhancement they may provide for these objects is usually fairly minimal even under skies that are already fairly dark.  The effect of these filters is most noticeable on the larger and more diffuse galaxies, as on the smaller ones, a similar enhancment can often be achieved just by bumping up the power a little.  Under moderate to severe light pollution, no filter will help galaxies, so your best bet is to find as dark an observing site as you can.  Clear skies to you.  BroadbandFiltersOnGalaxiesSmall.jpg


Edited by David Knisely, 11 February 2015 - 11:42 PM.


#4 T1R2

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Posted 11 February 2015 - 11:45 PM

I agree with David on this, but that 5" is only going to do so much, OTOH that 14"scope on small, tight, somewhat brighter spiral galaxies and elliptical, a bump up in mag is all you really need, given good clarity and seeing and dark skies.



#5 CeleNoptic

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Posted 11 February 2015 - 11:45 PM



I'd say the gas filter is the best bet.

+1 to the *gasoline filter*!

I'm not aware of any galaxy filter other than a dark spot. Baader M&SG? Well, it might be helpful in some certain situations but basically useless as any other filter.

Some measures reducing local LP and improving eye dark adaptation e.g. light blocking screens like  this or this, red goggles and observing hood/vest can help. But if your sky is heavily light polluted (e.g. Bortle 8-9) nothing really helps.  



#6 Starman1

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Posted 12 February 2015 - 01:09 AM

Even in light polluted areas, there are some things that might help:

--never look at anything closer than 45 degrees from the horizon.  Everything is best when it is high in the sky, so don't look at objects that are low.

--build light shields for yourself that block off all local light as well as, hopefully, all the sky below about 20 degrees from the horizon.  The air is always brighter nearer the horizon, so blocking it off will make the whole sky seem darker.

--use a little more power than normal.  If you usually view DSOs at 100X, say, use 120X instead.

--sit outside long enough to dark adapt as fully as the sky allows.  Even at my home in LA, that's at least a half hour.  You'll see more in the scope.  No reason to hinder your ability to see faint targets because you aren't even dark adapted.

--try blocking ALL peripheral light with a hood or by cupping your hands around the eyepiece.  This helps.

--use averted vision as much as you can to see the fainter parts (or in some cases the object).


Edited by Starman1, 12 February 2015 - 01:10 AM.


#7 Scanning4Comets

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Posted 12 February 2015 - 01:51 AM

[Don Pensack
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"The best light pollution filter is gasoline--you put it in your car and drive to darker skies."

 

Exactly what is on Don's SIG.

 

Another thing to consider is a larger scope to grab more light. Sure a 130 can see galaxies, but galaxies don't really start to shine until at least an 8" or bigger in darker skies.


Edited by Scanning4Comets, 12 February 2015 - 01:51 AM.


#8 russell23

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Posted 12 February 2015 - 05:44 AM

I've read that the 82A filter can give some extra pop to spiral galaxy features.

 

Dave



#9 Allan Wade

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Posted 12 February 2015 - 06:56 AM

I spent sometime comparing filters on galaxies, both at dark sites and light polluted sites. I have a Baader UHC-S which is a broadband filter, and it is a very poor filter to use for galaxies in any circumstance. My Baader Moon and Skyglow filter at best was acceptable to use in a light affected sky, but at a dark site I still preferred no filter. 

 

Observing galaxies is my passion, and I just stick to really dark skies plus all the usual tricks to see as much as I can.



#10 David Knisely

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Posted 12 February 2015 - 01:40 PM

I've read that the 82A filter can give some extra pop to spiral galaxy features.

 

Dave

 

In a large scope, that might be true, but the Lumicon Deep-sky filter lets through more light, so it is somewhat more effective (even though it still doesn't do a whole lot).  In fact, as far as the 82a is concerned, I use the Deep-sky filter *in place of* an 82a for viewing the orographic clouds and polar caps of Mars, so that filter can have more uses than  just on deep-sky objects.  Clear skies to you.



#11 turtle86

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Posted 12 February 2015 - 01:55 PM

I spent sometime comparing filters on galaxies, both at dark sites and light polluted sites. I have a Baader UHC-S which is a broadband filter, and it is a very poor filter to use for galaxies in any circumstance. My Baader Moon and Skyglow filter at best was acceptable to use in a light affected sky, but at a dark site I still preferred no filter. 

 

Observing galaxies is my passion, and I just stick to really dark skies plus all the usual tricks to see as much as I can.

 

I agree. For galaxies, it's aperture, dark skies, dark adaptation and averted vision for the fainter ones.



#12 MitchAlsup

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Posted 12 February 2015 - 03:30 PM

The best filter for galaxies is more aperture.



#13 russell23

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Posted 12 February 2015 - 03:55 PM

 

I've read that the 82A filter can give some extra pop to spiral galaxy features.

 

Dave

 

In a large scope, that might be true, but the Lumicon Deep-sky filter lets through more light, so it is somewhat more effective (even though it still doesn't do a whole lot).  In fact, as far as the 82a is concerned, I use the Deep-sky filter *in place of* an 82a for viewing the orographic clouds and polar caps of Mars, so that filter can have more uses than  just on deep-sky objects.  Clear skies to you.

 

 

I'm confused by that.  The transmission curve for the Lumicon deep sky is here:

 

http://www.astrosurf...umicon_deep.png

 

It cuts all wavelengths from ~540-640nm. 

 

I've looked at the transmission data for the 82A.  It is not that extreme at any point.

 

Dave



#14 David Knisely

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Posted 12 February 2015 - 05:54 PM

Well, some filters marked as 82a's have transmission curves and transmission maxima that are somewhat different from the true Wratten #82a.  The true #82a has a peak transmission of around 82% in the 4400 to 4500 angstrom range, with much of the rest of its passband being in the 65% to 75% range.  It is true that the 82a is not all that aggressive, especially when compared with an LPR filter like the Lumicon Deep-sky.  My Deep-sky has a peak transmission of about 93% and a huge deep notch that is designed to take out both the light pollution lines as well as the airglow lines (I replaced it with a 2" Orion Skyglow, which hits 97% at its peak).  Neither filter will help galaxies to a great degree however, which is the main point.  They are, however, rather effective for mercury vapor lighting, as the image below shows (too bad that lighting source is going out of favor):

 

BroadbandFilterComp3.jpg


Edited by David Knisely, 12 February 2015 - 06:00 PM.


#15 Bill Steen

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Posted 12 February 2015 - 07:05 PM

Thanks, everyone, for the help!  From what I read in the posts, I may purchase one of the Baader Moon and Sky Glow filters and try it out, or there is another cheaper knockoff by a company called Crystal View that is supposed to be similar.  I have some misgivings about purchasing from the second source simply because what they are doing may not be necessarily ethical if they have basically stolen the idea from Baader.  I am thinking about it.  For this little venture, the price on the Crystal View is probably about what I think one of that kind of filter is really worth to me.

 

I have been working some with an 82a filter and I think it is helping to knock out some of the light from low pressure sodium street lights in the addition.  I am thinking (hoping) something like the Baader filter might do just enough extra to actually make picking out some of the galaxies possible when they are not without it.

 

What I am doing is as much an intellectual quest of finding out exactly what I can do with the little Polaris 130 reflector from my back yard as anything.  I think of what I am doing much the same way as someone might compete in some particular class of sailing dinghy instead of taking out their yacht. 

 

Eventually, I am going to complete a review of this particular scope, but my thoughts on it are a bit convoluted just yet, and I need to get a much better feel for what it can really do.  It is a good little scope, but I do not want to lead a beginner astray with either too much good or bad.  I want to be able to say exactly what I have seen with the scope and what it took to accomplish the particular task.  I am finding it, as I have changed it to work with light pollution, to work pretty well a picking up nebulosity that I have not been able to see with smaller scopes, even though the image may not be as pristine as a small long refractor.  Right now, I am trying to find out how well it will work with galaxies, which seems to be a whole different quest than nebula in a light polluted situation.

 

Again, thanks!



#16 Starman1

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Posted 12 February 2015 - 07:21 PM

Neodymium-doped glass is not a trademark, nor an invention of Baader Planetarium.

It is not that which might give you pause about another brand--it is the optical quality of the glass itself.

Here is a user-review of the M&SG filter.

http://www.cloudynig...ow-filter-r2094

Note his comments about enhancement of galaxies.  It is very slight.

 

Since galaxies are full-spectrum objects, every visual-use filter will make them dimmer.  EVERY filter.

What you want is an improvement in contrast.

That comes with:

--larger scope

--darker skies


Edited by Starman1, 12 February 2015 - 07:21 PM.


#17 Simoes Pedro

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Posted 12 February 2015 - 07:42 PM

From my personal experience a baader neodymium or a CLS filter are useful to detect DSO.

 

Note that I used the term "detect". The improvement is very minor - galaxies will not "pop". But can be the difference between detecting and not detecting the object.

 

Due to its close to neutral tone I would recommend the neodymium.

 

I experience is limited to 4.5 mag skies. Under better skies I do not know whether the benefit is maintained.



#18 Bill Steen

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Posted 12 February 2015 - 08:10 PM

Thanks, Don and Simoes!



#19 David Knisely

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Posted 12 February 2015 - 11:28 PM

 

Even an 82A filter I have seems to help a little bit, but I really need a little more assistance.  I am not really trying to see any detail, just be able to say, "There it is!" with more confidence that I really am seeing an indication.

 

I was wondering which of the light pollution/moon glow filters or any other filters for that mater would be truly helpful with this endeavor.  Probably something in the $90 price range would be about top dollar that I would be willing to spend on a 1.25 inch filter at this time or in the near future.

 

 

Not all galaxies are the same, so for all galaxies the answer probably isn't the same.

 

For instance, the HII regions in galaxies might respond to an H-alpha filter; Table I

in the following paper gives sources of HII finder charts for more than 100 galaxies:

  Hodge PW. PASP, vol. 86, pp. 845-860 (Dec., 1974) 

 

Most of these are listed in Hodge's Atlas of HII Regions in Galaxies. In the 1982 edition,

the galaxies with the most HII regions are: M81 (803), IC 342 (668), NGC 2403 (606),

NGC 6946 (540), NGC 1232 (529), and M101 (471).

 

Of course, you should probably get some observing reports of these galaxies through

an H-alpha filter before spending the 200 bucks.

 

                                                                                     -- catalogman

 

 

An H-alpha filter is only useful on galaxies if you are using an image intensfier or a camera to view galaxies.  Visually, an H-alpha filter is almost useless, since the human eye is nearly blind to that wavelength at the low light levels we deal with when viewing with the eye alone at the telescope.  Some with larger apertures use a regular OIII filter to enhance some HII regions in other galaxies, and I have even noticed a little enhancement of these regions when using a regular narrow-band nebula filter.  Clear skies to you.



#20 GlennLeDrew

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Posted 13 February 2015 - 05:52 AM

A filter which has notches in its transmission spectrum to knock down a goodly amount of the more egregious light pollution/natural air glow, while passing as much other light as possible, could be a worthwhile galaxy filter. Even the Orion Skyglow Imaging filter could offer visual improvements here.

#21 Starman1

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Posted 13 February 2015 - 10:50 AM

I have an old Sirius Optics (defunct company) CE-1 filter that essentially does just that, and the light reduction in the notches is only about 50%.

I have tried it on galaxies in dark skies, and it seemed to help the visibility of some HII regions in M33.  Other than that, every galaxy appeared better without the filter.

At some more light-polluted sites, the filter seemed to increase the amount of light scatter.

Glenn's hypothetical filter would have to have excellent anti-reflection coatings, be a single layer filter (NO laminations) and even then severe light pollution would be a problem.



#22 GlennLeDrew

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Posted 13 February 2015 - 03:49 PM

Don,
My 'hypothetical' filter? ;)

For video cams such specimens as described do improve the visibility of continuum sources (galaxies and at least some reflection nebulae, under moderate light pollution, and should do so visually as well.

Why the requirement for no more than a single layer? And superlative AR coatings? Narrow band nebula filters do sterling work with their multitudinous layers--and their near mirror-like reflectivity. I don't see how it's gotta be all or nothing. To me there's nothing intrinsically disadavantagous with 'intermediate' levels of LP rejection, as long as the *ratio* of desired light passed to unwanted light blocked has increased.

#23 Starman1

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Posted 13 February 2015 - 04:09 PM

Glenn, what I meant by "single layer" was a single glass element without a second piece of glass laminated to it.

The coatings themselves would be 45-75 layers thick.

And the AR coatings would be to prevent reflections internal to the glass, which cause significant problems for broadband filters in heavy light pollution.

And I'm all in favor of notch filters.  They can work wonders without significantly dimming anything.

But other than the neodymium glass filters, who makes such an item commercially today?



#24 jeffmac

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Posted 13 February 2015 - 08:29 PM

Back to the picture that David Knisely posted of the galaxy with and without Lumicon Deepsky filter, I occasionally use my Deepsky filter on galaxies and do perceive a contrast gain. Not a perception of added detail but an obvious gain in contrast between the galaxy and the surrounding space. So, it is useful in this regard and may be useful in detection of faint galaxies.



#25 Achernar

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Posted 13 February 2015 - 08:50 PM

The best filter for galaxies is a full tank of gas and a trip to at least a reasonably dark site.

 

Taras




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