Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

A filter for embedded open clusters?

  • Please log in to reply
21 replies to this topic

#1 Enkidu

Enkidu

    Explorer 1

  • *****
  • topic starter
  • Posts: 66
  • Joined: 16 Oct 2017
  • Loc: EU

Posted 17 June 2019 - 05:32 AM

Has anyone considered a "nebula-killer" filter for embedded open clusters (eg an inverted UHC with the emission lines notched/suppressed)? I imagine stellar contrast in the Trapezium and clusters like NGC6530, 6611, or 2244 would be a refreshing and welcome sight.

 

Twilight / light pollution (or small exit pupils) can provide something similar... but a filter could offer complementary views, isolating another facet and enhancing detail/appreciation of the whole object. Perhaps useful with a UHC in dual-filtered binoculars?

 

Is this a crazy idea?


Edited by Enkidu, 17 June 2019 - 08:03 AM.


#2 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 17 June 2019 - 11:35 AM

I.e. suppress the light of the nebula without suppressing a lot of star light.

This is surprisingly easy to do:

View without a filter and use higher powers.

1) the background, and nebula grow dimmer, while the stars do not.

2) you don't suppress the starlight right at the wavelengths the eye is most sensitive to.

 

M42 is a bad example, because it emits energy at at least 11 different visible wavelengths.

Any filter that suppressed that energy would kill the stars.

Now, if you could see in the infrared...........


  • Augustus likes this

#3 Enkidu

Enkidu

    Explorer 1

  • *****
  • topic starter
  • Posts: 66
  • Joined: 16 Oct 2017
  • Loc: EU

Posted 17 June 2019 - 12:01 PM

Yep, I mentioned smaller exit pupils above : )

 

One-off custom filters are possible now, so I thought it'd be worth exploring whether this can be done a better way (or while using fixed mag optics)...

 

I'd be happy to see the wavelength data for M42, that sounds interesting.



#4 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 17 June 2019 - 12:18 PM

http://www.astrosurf...II/m42/m42.html


  • Dave Mitsky and Enkidu like this

#5 Roragi

Roragi

    Viking 1

  • -----
  • Posts: 516
  • Joined: 24 Oct 2013
  • Loc: Milky Way, Spain - Madrid

Posted 18 June 2019 - 05:27 AM

Actually I look for open clusters with integrated nebulae, I do not like the idea of killing.


  • havasman likes this

#6 quazy4quasars

quazy4quasars

    Ranger 4

  • *****
  • Posts: 307
  • Joined: 12 Jul 2014

Posted 18 June 2019 - 10:18 AM

I.e. suppress the light of the nebula without suppressing a lot of star light.

This is surprisingly easy to do:

View without a filter and use higher powers.

1) the background, and nebula grow dimmer, while the stars do not.

2) you don't suppress the starlight right at the wavelengths the eye is most sensitive to.

 

M42 is a bad example, because it emits energy at at least 11 different visible wavelengths.

Any filter that suppressed that energy would kill the stars.

Now, if you could see in the infrared...........

Looking at the relative flux of those spectra, the effectively obstructive emission lines are the H beta and O III doublet,   followed by the H alpha spike, which, though mildly stronger, can probably be ignored since it's well outside the scotopic vision zone and already attenuated by 3-4 mags visual.   I think any major reduction of the OIII doublet, (which after all, straddles the scotopic sensitivity maximum) along with higher magnification, would get you pretty much there, i.e. in the max contrast ballpark  A gold diagonal would be an idea... if perhaps a half baked one...   


Edited by quazy4quasars, 18 June 2019 - 10:43 AM.

  • Enkidu likes this

#7 Enkidu

Enkidu

    Explorer 1

  • *****
  • topic starter
  • Posts: 66
  • Joined: 16 Oct 2017
  • Loc: EU

Posted 18 June 2019 - 01:42 PM

Actually I look for open clusters with integrated nebulae, I do not like the idea of killing.

Nebulae are possibly my favorite deep sky objects to observe. This is why I'd like to see these regions in more unusual ways.

 

It would be similar to using a nebula filter on nearby galaxies to isolate star-forming knots: You wouldn't observe that way all the time, but it can deepen the integrated view when you "turn the lights back on."

 

A gold diagonal would be an idea...

Gold diagonal! What an interesting out-of-the-box suggestion.



#8 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 18 June 2019 - 04:03 PM

The spectrum of gold reflection is really superb in the red and infrared.

But it transmits poorly below ~500nm, which would seriously dim the stars.

A "notch" filter from 480nm-510nm might be worthy of experimentation.

Baader has a filter that mimics a gold transmission called the "495 Long-Pass filter".

It might be worth a shot.



#9 quazy4quasars

quazy4quasars

    Ranger 4

  • *****
  • Posts: 307
  • Joined: 12 Jul 2014

Posted 20 June 2019 - 10:44 AM

The spectrum of gold reflection is really superb in the red and infrared.

But it transmits poorly below ~500nm, which would seriously dim the stars.

A "notch" filter from 480nm-510nm might be worthy of experimentation.

Baader has a filter that mimics a gold transmission called the "495 Long-Pass filter".

It might be worth a shot.

Jeez, can't s guy come in here, offer some goofball notion, straight out of left field, off the top of his head, without some knowledgeable person immediately explaining in clear English, devoid of hyperbole, exactly why its a goofball notion?

 

That was a rhetorical question. Good Day to you.



#10 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 20 June 2019 - 12:16 PM

Jeez, can't s guy come in here, offer some goofball notion, straight out of left field, off the top of his head, without some knowledgeable person immediately explaining in clear English, devoid of hyperbole, exactly why its a goofball notion?

 

That was a rhetorical question. Good Day to you.

lol.gif

Experimentation is what leads to revelations.

A gold-coated diagonal would be quite expensive compared to a filter.

I was suggesting there was a cheaper way to test the hypothesis using an affordable filter.

Thanks for the compliment, by the way.

 

Look at the curve of reflectivity of Aluminum, silver and gold here and compare to the Baader long pass filter:

Attached Thumbnails

  • 350px-Image-Metal-reflectance.png
  • ofil-bp-fcfy-1-2.jpg

Edited by Starman1, 20 June 2019 - 12:17 PM.


#11 quazy4quasars

quazy4quasars

    Ranger 4

  • *****
  • Posts: 307
  • Joined: 12 Jul 2014

Posted 20 June 2019 - 01:28 PM

  Interesting!  I had a buddy who worked at Lumicon back in the day; I wish I had picked his brain a lot more.  I imagine there are as many creative ways to combine properties of reflection, transmission, absorbance , diffraction, resonance/cancelling -as there are colors.  I was just thinking how gold is somewhat the inverse of cyan(OIII)

 

  An extremely tight OIII rejection might, for example, be accomplished by abusing an OIII narrow bandpass filter (as a diagonal, or deflector), IF the case were that the normally "unwanted" broad wavelength bands are reflected back(rather than absorbed or scattered),  of course; and many filters pass-bands change with  the "incident angle" of the incoming light too, so...  Hey, one half baked idea deserves another!  That goes for compliments as well. Thanks!

 

 I always enjoy your considered input, Starman, you're a guy who can appreciate goofy revelations for their own sake, just as I enjoy wantonly polluting the minds of the easily confused who might wander into my path of disruption.  confused1.gif bow.gif waytogo.gif    Yeah, it's the Devil's work, but, I do a truly lousy job!


Edited by quazy4quasars, 20 June 2019 - 02:19 PM.

  • Starman1 likes this

#12 sgottlieb

sgottlieb

    Apollo

  • *****
  • Posts: 1359
  • Joined: 22 Jul 2007
  • Loc: SF Bay area

Posted 20 June 2019 - 09:47 PM

I've viewed several planetaries through a reverse UHC filter -- with the idea of improving the visibility of the central star (think M57, etc).  The first time was back in the early to mid-80's when Jack Marling produced a few prototype filters with the idea of possibly marketing such a filter.  But the improvement was subtle at best and generally required a large scope to appreciate a difference.  Still it was fun and weird to see the planetary nearly disappear!


  • quazy4quasars and Enkidu like this

#13 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 7551
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 21 June 2019 - 02:53 PM

It is an interesting idea, might work for a few things, such as providing some contrast for the G/H/I stars in the Trapezium.  Unfortunately, removing 30nm in this portion of the visual band is going to result in about 30% reduction in scotopic visual response from the stars themselves.  This could be in the range of nearly 0.4 magnitude loss in brightness.  As Steve says, you would likely need considerable excess aperture to observe the benefit provided by the darkened background.

 

I did a related thing with some heavily reddened galaxies in or neighboring the Local Group, using yellow filters to suppress the blue, since they were relatively blue deficient.  The enhancement was slight.


  • Enkidu likes this

#14 quazy4quasars

quazy4quasars

    Ranger 4

  • *****
  • Posts: 307
  • Joined: 12 Jul 2014

Posted 21 June 2019 - 04:13 PM

It is an interesting idea, might work for a few things, such as providing some contrast for the G/H/I stars in the Trapezium.  Unfortunately, removing 30nm in this portion of the visual band is going to result in about 30% reduction in scotopic visual response from the stars themselves.  This could be in the range of nearly 0.4 magnitude loss in brightness.  As Steve says, you would likely need considerable excess aperture to observe the benefit provided by the darkened background.

 

I did a related thing with some heavily reddened galaxies in or neighboring the Local Group, using yellow filters to suppress the blue, since they were relatively blue deficient.  The enhancement was slight.

Agree.  Removing 480-510nm  is too much;  If you strongly diminish the OIII (forbidden!) doublet, that would only remove say 4950-5015 angstrom  or ~7 nm lost (assuming a sharp cutoff both sides)  So now you're losing 8-12 percent of the starlight along with ~80 percent of the nebula, effective.  Add in some higher magnification too and you've got 2 -3 magnitudes improvement in SB contrast.

 

Any enhancement of reddened galaxies... is good; at least a little, eh? I'll have to try that.



#15 JimK

JimK

    Skygazer

  • *****
  • Posts: 1143
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 03 July 2019 - 06:48 PM

...  Baader has a filter that mimics a gold transmission called the "495 Long-Pass filter".

It might be worth a shot.

While at a dark site (Rocky Mountain Star Stare) last week I decided to try out this idea on the Lagoon Nebula (M8/NGC 6533) in Sagittarius.  I was using 14-inch optics at about 75x with dark skies of ~22.0 MPSAS zenith (per my SQM-L device) around midnight.  Unintentionally, I first "bleached" my eyeballs by viewing this object unfiltered.

 

Upon using a 610nm red long pass filter, I immediately noticed the red-colored dots of light, however there were much fewer stars (only about 1/2 dozen), no nebulosity, and the overall view was very dark.  After several more minutes of observation, the number of stars seemed to double, with more faint stars becoming visible, as well as being able to see a dark lane dividing the east and west areas of stars.  Upon still more viewing, some very faint nebulosity glow of the bright western area (NGC 6523), but not the eastern area (NGC 6526), was noticed.  The vivid red dots reminded me of viewing carbon stars R Lep and T Lyr.

 

I then tried using a 495nm yellow long pass filter (since I had one readily available), but found it was not effective in reducing nebulosity.

 

The results of this experiment were very pretty/colorful, but not too encouraging as a means of removing just nebulosity from a star cluster, because the view was very, very dark and many stars of a cluster are also filtered out. [when using a red filter, and unsuccessful when using a yellow filter]


Edited by JimK, 03 July 2019 - 06:51 PM.

  • Enkidu likes this

#16 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 03 July 2019 - 07:48 PM

Filtering out just the nebula would require a notch filter that removes 480 to 505nm.

#17 JimK

JimK

    Skygazer

  • *****
  • Posts: 1143
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 04 July 2019 - 12:06 AM

Filtering out just the nebula would require a notch filter that removes 480 to 505nm.

Probably true -- but it was fun to experiment with the 610nm and 495nm longpass filters, based on CN discussions!



#18 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 77160
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 04 July 2019 - 12:55 AM

One could do a calculation of the surface brightness of the Airy disk versus the surface brightness of the nebula.. I am thinking that with a 10 inch scope, the Airy disk is approximately 0.93 square arc-seconds in area.  That is actually based on the diameter to the first minimum so the actual area is somewhat smaller than this, making the surface brightness somewhat greater than this.  But this is just a ball park calculation.  

 

This suggests that for a 10 inch, the surface brightness in mpsas of a star is approximately equal to it's visual magnitude.  This puts an upper limit on the contrast possible by increasing the magnification.  

 

Just kind of thinking out loud.

 

Jon


  • Enkidu likes this

#19 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 41730
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 04 July 2019 - 10:18 AM

Except the star won't dim with increased magnification, while the nebula will.

Also, sometimes seeing a faint star requires getting some space around it.

I see the G. H, and I stars in M42, or the central star in M57 more regularly in fantastic seeing at 400x than at any lower powers,

and all are on top of nebulosity.



#20 Enkidu

Enkidu

    Explorer 1

  • *****
  • topic starter
  • Posts: 66
  • Joined: 16 Oct 2017
  • Loc: EU

Posted 05 July 2019 - 12:42 AM

Interesting thoughts and experiences from some very knowledgeable people.

 

 

I decided to try out this idea on the Lagoon Nebula (M8/NGC 6533) in Sagittarius.  I was using 14-inch optics at about 75x with dark skies of ~22.0 MPSAS zenith

Thanks very much for testing this idea with large aperture under dark skies!

 

 

Upon using a 610nm red long pass filter, I immediately noticed the red-colored dots of light, however there were much fewer stars (only about 1/2 dozen), no nebulosity, and the overall view was very dark.  After several more minutes of observation, the number of stars seemed to double, with more faint stars becoming visible, as well as being able to see a dark lane dividing the east and west areas of stars.

Purkinje effect perhaps?

 

 

I then tried using a 495nm yellow long pass filter (since I had one readily available), but found it was not effective in reducing nebulosity.

Maybe a 570nm amber filter would be better. By this rationale, a 470nm BandPass would also act as a rudimentary UHC filter but I've not heard of anyone doing that(?)...

 

 

One could do a calculation of the surface brightness of the Airy disk versus the surface brightness of the nebula..

I've wondered about this! Thanks for bringing it up.

 

By the way, Astronomik can make a limited run of (50) custom 2" "EOC" filters according to Don's proposed wavelength suppression.


Edited by Enkidu, 05 July 2019 - 12:43 AM.


#21 JimK

JimK

    Skygazer

  • *****
  • Posts: 1143
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 05 July 2019 - 11:58 AM

... the Lagoon Nebula (M8/NGC 6533) in Sagittarius ...  Unintentionally, I first "bleached" my eyeballs by viewing this object unfiltered.

 

Upon using a 610nm red long pass filter, I immediately noticed the red-colored dots of light, however there were much fewer stars (only about 1/2 dozen), no nebulosity, and the overall view was very dark.  After several more minutes of observation, the number of stars seemed to double, with more faint stars becoming visible, as well as being able to see a dark lane dividing the east and west areas of stars.  Upon still more viewing, some very faint nebulosity glow of the bright western area (NGC 6523), but not the eastern area (NGC 6526), was noticed.  The vivid red dots reminded me of viewing carbon stars R Lep and T Lyr.

...

 

...

Purkinje effect perhaps?

...

Probably more of regenerating my eyeball "opsins" after looking at the nebula unfiltered when it was very bright.  Just like trying to see a faint, small star cluster after gazing at Jupiter -- it takes a while to recover from those bright sky objects! 



#22 JimK

JimK

    Skygazer

  • *****
  • Posts: 1143
  • Joined: 18 Sep 2005
  • Loc: Albuquerque, NM USA

Posted 05 July 2019 - 12:07 PM

...

Maybe a 570nm amber filter would be better. By this rationale, a 470nm BandPass would also act as a rudimentary UHC filter but I've not heard of anyone doing that(?)...

...

I don't have a 570nm amber longpass filter, but a 470nm teal bandpass filter is in my gear, so now you have given me another idea as an experiment. Now I just need a (relatively) moonless, clear night.

 

Thanks!


  • Enkidu likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics