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Galaxy Filters for the Backyard

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#26 faackanders2

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Posted 07 April 2021 - 05:25 PM

I have a manual dob and wide AFOV/TFOV eyepieces do help me find objects even dim galaxies.  I therefore disagree with the "skinny filter" narrow AFOV/TFOV eyepiece with the exception when a galaxy is next to a bright star and the narrow FOV can be panned to eliminate that star but still keep the object of interest in the FOV.


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#27 brentknight

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Posted 07 April 2021 - 07:10 PM

Unfortunately there are no Galaxy filters, except the DGM GCE (Galaxy Contrast enhancement) filter.  I do have that and on M31 from a dark sky site I could not tell a difference, but two other amature astronomers said the 2" DGM GCE made an improvement.

 

I don't think I'd expect much from any filter for galaxies at a dark site.  I have seen some improvement with open spirals where HII regions are visible.  I'm most interested in getting some contrast  improvement at the house... 



#28 BillP

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Posted 07 April 2021 - 07:53 PM

As you can see from the graph, the the Lumicon Deep Sky and the Baader UHC-S are essentially the same except for the far red.  Interestingly, the DGM GCE and the Baader M&S are similar over most of their spectrum with the major difference being that the M&S lets the green spectrum around 550 thru while the GCE blocks it.

 

I do not live in a very light polluted area and my SQM is around 21.3 on moonless nights.  However, I do observe fainter stuff when the Moon is up and the SQM is 20 or a tad brighter.  Under those circumstances I found that the Baader M&S amazingly does a nice job of darkening the background sky while keeping the nebula/galaxy still bright (i.e., a contrast enhancement).  I have all the filters mentioned above except the UHC-S.  Of the 3 I actually prefer the Lumicon Deep Sky as overall doing the best job (subtly) of the 3.  After that the M&S, then the GCE last.  So to the OP I would say just stick with your UHC-S.

 

temp.jpg


Edited by BillP, 07 April 2021 - 09:15 PM.

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#29 Dave Mitsky

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Posted 07 April 2021 - 11:23 PM

David Knisely's review of the GCE filter can be seen at https://www.cloudyni...ce-filter-r1595
 

https://www.omegafil...om/product/4380


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#30 russell23

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Posted 07 April 2021 - 11:35 PM

A quick follow-up to my earlier post.  I tried both the Astronomik B-band filter and the Baader 495 Longpass filter on a few galaxies.  There was some very mild gain with the 495 LP and a loss of visible galaxy extent with the B-band.  I wouldn’t consider either of these filters worth it for galaxies.

 

The Astronomik B-band filter has some benefit for emission nebula when the exit pupil is less than ~1.5mm.  


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#31 brentknight

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Posted 08 April 2021 - 02:33 AM

A quick follow-up to my earlier post.  I tried both the Astronomik B-band filter and the Baader 495 Longpass filter on a few galaxies.  There was some very mild gain with the 495 LP and a loss of visible galaxy extent with the B-band.  I wouldn’t consider either of these filters worth it for galaxies.

 

The Astronomik B-band filter has some benefit for emission nebula when the exit pupil is less than ~1.5mm.  

Russell,

 

What were your conditions?  Neighborhood lights?



#32 russell23

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Posted 08 April 2021 - 08:26 AM

I live in a rural area.  There are no neighbor lights.  However, a few miles away to the south is a scrap metal facility that brightens the sky in that direction.  I would say in the south my skies have shifted from green to yellow because of that facility.  In the north my skies are still green.  


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#33 brentknight

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Posted 09 April 2021 - 10:31 AM

I guess I should feel lucky that the offending lights in my backyard are limited to the yellow/orange color range.  To the north I have more generic rural/suburban light pollution and I would think the UHC-S would not be much benefit.  Maybe I can come up with some way to quantify the contrast differences on particular galaxy types with and without the filter.  Anyone have any ideas on how I might do that?



#34 RLK1

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Posted 09 April 2021 - 12:02 PM

I guess I should feel lucky that the offending lights in my backyard are limited to the yellow/orange color range.  To the north I have more generic rural/suburban light pollution and I would think the UHC-S would not be much benefit.  Maybe I can come up with some way to quantify the contrast differences on particular galaxy types with and without the filter.  Anyone have any ideas on how I might do that?

I don't think you'll be able to quantify the contrast differences on particular galaxy types, with and without filters, in a light polluted environment. In general, those galaxies with higher surface brightness will generally respond better to the use of a filter while those with a low surface brightness will escape detection, with or without a filter, in a light polluted environment. Some galaxies will have regions within them that respond more favorably to a filter. I would avoid the advice of the graph-obsessed posters and use the UHC-S and/or equivalent while observing from a moderately light polluted area. I typically use several broadband filters for observations of various galaxies with my 16 f4.5 dob and my high ambient light polluted skies usually allow for a 4.3 or so visual magnitude and a faintly outlined milky way at the zenith. The more aperture the better, but as Ed Ting notes, "large mirrors collect and reflect light indiscriminately" so unless you're doing something to mitigate the effects of the pollution,  you're likely to see only a washed-out light fogged view of most galaxies in the eyepiece. 


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#35 brentknight

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Posted 09 April 2021 - 12:46 PM

::  SNIP  ::  In general, those galaxies with higher surface brightness will generally respond better to the use of a filter while those with a low surface brightness will escape detection, with or without a filter, in a light polluted environment.

You bring up a great point.  Would a galaxy that's not visible without a filter (just below the threshold of visibility) show faintly with an appropriate filter?  Somewhere near the optimal magnification/exit pupil?

 

So far I've noticed a slight improvement in contrast using the filter with galaxies that I can see without a filter, but I've not tried to detect one that I can't quite make out.  Perhaps there's a point where magnification and filtration cancel each other.  Magnification beyond that point dims the image more than the filter can enhance.



#36 RLK1

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Posted 09 April 2021 - 12:57 PM

"Would a galaxy that's not visible without a filter (just below the threshold of visibility) show faintly with an appropriate filter?  Somewhere near the optimal magnification/exit pupil?"

In my experience, most definitely. In some cases,under my observing conditions, I'll vary the focal length of the eyepiece and hence the magnification/exit pupil with a filter to detect a galaxy that would otherwise be invisible without doing so...


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#37 Starman1

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Posted 09 April 2021 - 06:14 PM

You bring up a great point.  Would a galaxy that's not visible without a filter (just below the threshold of visibility) show faintly with an appropriate filter?  Somewhere near the optimal magnification/exit pupil?

 

So far I've noticed a slight improvement in contrast using the filter with galaxies that I can see without a filter, but I've not tried to detect one that I can't quite make out.  Perhaps there's a point where magnification and filtration cancel each other.  Magnification beyond that point dims the image more than the filter can enhance.

Any filter will dim the galaxy.

Experimentation with magnification might be more fruitful.

 

The galaxy gets dimmer with increased magnification, but it also gets larger, and larger makes it more visible.

There is a point where the two curves cross that is the optimum magnification for the object, and it will be different in a bright sky

than it will in a dim sky.  But it may end up, indeed likely will end up, making the galaxy more visible than a filter would.


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#38 RLK1

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Posted 09 April 2021 - 06:29 PM

Any filter will dim the galaxy.

Experimentation with magnification might be more fruitful.

 

The galaxy gets dimmer with increased magnification, but it also gets larger, and larger makes it more visible.

There is a point where the two curves cross that is the optimum magnification for the object, and it will be different in a bright sky

than it will in a dim sky.  But it may end up, indeed likely will end up, making the galaxy more visible than a filter would.

"Any filter will dim the galaxy."

It dims (blocks) the light pollution more so, making the contrast between the galaxy and the milky white light polluted and fogged view in the eyepiece more evident. Not on all of them but on many of them. I'd estimate I'm able to observe about 70% of the galaxies that I'm after with a filter, concurrent with my observing conditions and equipment. 


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#39 j.gardavsky

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Posted 10 April 2021 - 10:18 AM

"Any filter will dim the galaxy."

It dims (blocks) the light pollution more so, making the contrast between the galaxy and the milky white light polluted and fogged view in the eyepiece more evident. Not on all of them but on many of them. I'd estimate I'm able to observe about 70% of the galaxies that I'm after with a filter, concurrent with my observing conditions and equipment. 

This is correct, but still not understood by lots of the observers.

 

The filters do not amplify the light of the nebulae or galaxies,

but they suppress the light of the unwanted wavelengths in the sky background glow,

if it is the natural sky glow, or a glow from the LP.

 

The filters I am using for the galaxies are the UHC (for the HII regions), the blue(RGB)CCD 400nm - 510nm for the outer spiral arms regions (OB stars associations), the long pass yellow filters for the dark lanes around the core. Sometimes, the Moon Sky Glow Neodymium filter finds a good use.

 

The choice of the filters is dictated by the astrophysics, and not by the lists or casual shootouts.

 

Best,

JG


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#40 BillP

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Posted 10 April 2021 - 10:34 AM

The filters I am using for the galaxies are the UHC (for the HII regions), the blue(RGB)CCD 400nm - 510nm for the outer spiral arms regions (OB stars associations), the long pass yellow filters for the dark lanes around the core. Sometimes, the Moon Sky Glow Neodymium filter finds a good use.

 

The choice of the filters is dictated by the astrophysics, and not by the lists or casual shootouts.

This is excellent advice...for when you have a good view of the galaxy in the first place.  So yes, the nature of the astrophysics of the particular galaxy can guide one on filter choices to see/detect those particular features better.

 

However, for many, perhaps the majority, they are looking for filters as a way to even get a hint or view of a galaxy in the first place!  In their case, leveraging astrophysics of the galaxy is not the answer.  The best "filter" in this use-case is quite definitely IMO the one that Don suggests, the GAS filter to drive to a darker and higher observing location lol.gif


Edited by BillP, 10 April 2021 - 10:37 AM.

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#41 Supernova74

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Posted 10 April 2021 - 11:45 AM

I’ve found in most part filters on galaxies for myself anyway have found of not much use and prefer to use averted vision which I’ve found really helps on the M51 in very mediocre class 6 sky’s when the sky is at its darkest.


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#42 RLK1

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Posted 10 April 2021 - 12:58 PM

From my observing session last night in front of my light polluted home with my 16" f4.5 dob, I was able to observe a total of 42 galaxies during a seven hours session. Virtually all of the observations were with a 10mm ethos eyepiece and either a celestron baader uhc light pollution filter or an astrotech broadband filter under highly transparent skies with a limiting visual magnitude of 4.95, the latter being the dimmest star I could see in ursa minor with averted vision. Seeing was so so, ranging from poor to average with intermittent breezes at around 15 mph. 

In general, I found the deepest I could go was a visual magnitude of around 12 and a surface brightness of approximately 13.5. I determined the celestron baader uhc filter gave better resolution of the notch in the black eye galaxy and of the spiral structure in m51 while the astrotech broadband delivered a bit brighter image of fainter galaxies but both allowed for some resolution of ngc 4147, a small globular cluster in coma berenices which can be a challenge for a 14" instrument under dark skies. The most challenging object I observed was Holmberg 342a, aka ngc 4145,  with a visual magnitude of 11.3 but surface brightness of only 14.6. I tried but failed to detect nearby ngc 4151, a type 1 Seyfert galaxy, that the "Observer's Guide" notes has a nucleus that varies by a magnitude with the maxima reaching 12.4. 

I can confidently state that all of my observations were clearly superior with a filter than without one and I wouldn't consider observing without a filter in much the same manner that most observers wouldn't observe without a paracorr in place on a fast reflector. 


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#43 Miranda2525

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Posted 10 April 2021 - 01:27 PM

Went observing for a good 3 hours last night. I have a Celestron UHC/LPR, which is close to the same as a broadband filter. I tried using it on M-64. The filter did *nothing* to enhance the view. In fact it was better looking without the filter in place.

 

I drove about 30 min away from city lights.


Edited by Miranda2525, 10 April 2021 - 01:29 PM.

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#44 j.gardavsky

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Posted 10 April 2021 - 01:53 PM

Re post #40

 

Not everybody will find an easy access to a better and safe observing location somewhere, and not everybody will be able to afford the Gas Filter frequently.

 

In an extreme case,

you could recommend people to move for a couple of month to Chile, and then to Australia, in order to avoid using the non-Gas astronomy filters.

 

Lots of members on this Forum have decided for the hobby astronomy, as they can enjoy it from their homes.

 

Otherwise, there is a mass of other hobbies, which require the Gas, as they can't be enjoyed from the backyard, or from the environments of their homes.

 

JG


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#45 Supernova74

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Posted 10 April 2021 - 02:05 PM

Re post #40

 

Not everybody will find an easy access to a better and safe observing location somewhere, and not everybody will be able to afford the Gas Filter frequently.

 

In an extreme case,

you could recommend people to move for a couple of month to Chile, and then to Australia, in order to avoid using the non-Gas astronomy filters.

 

Lots of members on this Forum have decided for the hobby astronomy, as they can enjoy it from their homes.

 

Otherwise, there is a mass of other hobbies, which require the Gas, as they can't be enjoyed from the backyard, or from the environments of their homes.

 

JG

Sometimes JG you just have to make do what’s available to you i guess gas filters!?


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#46 brentknight

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Posted 10 April 2021 - 02:23 PM

Went observing for a good 3 hours last night. I have a Celestron UHC/LPR, which is close to the same as a broadband filter. I tried using it on M-64. The filter did *nothing* to enhance the view. In fact it was better looking without the filter in place.

 

I drove about 30 min away from city lights.

I don't doubt this observation at all.  I think my point in all this discussion is really just about detecting galaxies (and more likely just faint ellipticals) from moderately light polluted skies.  Even where there are broad-spectrum streetlights in the suburbs, these filters might not help much (like my northern skies).  I mentioned earlier, my backyard sky is gently flooded with yellow lights from the neighbors nighttime yard display.  I know of no other way to remove this light other than to experiment with these filters, and to some extent it appears to work and others seem to agree.  From a dark site, I would likely only use these filters to bring out details within the brighter galaxies - not so much to detect them.

 

We most definitely have to deal with the circumstances we are given - and just hope things don't get worse...


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#47 25585

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Posted 10 April 2021 - 02:24 PM

brentknight, how do you find seeing galaxies in your C8 compared to 14" Dob? Obviously much dimmer in the C8, but as its less aperture & longer FL, it may give better contrast and pick up less unwanted light, for what you can see in 8". 

 

Filters are effectively aperture-reducing as the light you see is cut. Therefore a longer FL, larger FR, shorter unfiltered scope, with no filter might partially help.

 

I have decorative sodium bulb lamps in my road, and my C8 & 10" F6 Dob, are less affected than my 12" & 10" F5s.


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#48 brentknight

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Posted 10 April 2021 - 02:30 PM

Sometimes JG you just have to make do what’s available to you i guess gas filters!?

I have a Bortle 3 site less than 2 hours away from me (SQM 21.75).  The last time I was up there I scanned around the spiral arms of M33 with the same UHC-S filter.  It was marvelous.  I used the filter with A/V and with higher magnifications.  I could have spent the entire evening tracking down named NGC regions in both prominent arms.  What I see from the house is a pale shadow of what I can see up there, but I can see many more objects from my yard since I'm here almost all the time.


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#49 brentknight

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Posted 10 April 2021 - 02:40 PM

brentknight, how do you find seeing galaxies in your C8 compared to 14" Dob? Obviously much dimmer in the C8, but as its less aperture & longer FL, it may give better contrast and pick up less unwanted light, for what you can see in 8". 

 

Filters are effectively aperture-reducing as the light you see is cut. Therefore a longer FL, larger FR, shorter unfiltered scope, with no filter might partially help.

 

I have decorative sodium bulb lamps in my road, and my C8 & 10" F6 Dob, are less affected than my 12" & 10" F5s.

I've only had the C8 since early January and really haven't had much chance to use it on galaxies around here.  I'll have to experiment with that sometime too, but in the past when I've brought multiple telescopes out, I get fixated on one or the other and then the unused one just starts collecting dew...

 

My thoughts are that it would show fewer galaxies than the 14" would (in terms of the faintest magnitudes I could detect), but on those objects that were visible in both scopes I would think the C8 would show those objects better without a filter.  I really don't know though.



#50 Supernova74

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Posted 10 April 2021 - 02:51 PM

I have a Bortle 3 site less than 2 hours away from me (SQM 21.75).  The last time I was up there I scanned around the spiral arms of M33 with the same UHC-S filter.  It was marvelous.  I used the filter with A/V and with higher magnifications.  I could have spent the entire evening tracking down named NGC regions in both prominent arms.  What I see from the house is a pale shadow of what I can see up there, but I can see many more objects from my yard since I'm here almost all the time.

Lol got ur now it’s was JG terminology first time I’ve heard UHC,OIII being gas filters that’s all well one day I hope I nearly moved to a class 4 sky’s big improvement over my current class 6,yes i used my Astronomic UHC for the first time on M42 yes was amazed with the nebulosity stretching out never seen before unaided with a filter 


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