8 replies to this topic

[azure1961p]

Some folks in the eyepiece forum on the plossl, orthos  versus Brandon oculars have mentioned using a light blue filter , I'm guessing written 80a?, as the galaxies as a r3sult appear plainer. These are seasoned  respectable observers so I take it seriously.  Here's what I'm guessing....

 

The pale blue serves to suppress the redder spectrums as in those orangey street lights and such.  You kno the common ones I'm talking about. I forget which is sodium vapor etc. etc..   Too some galaxies, younger still star forming associations would certainly *favor* a light blue filter.  We all kno as well, the blue/green sensitive area of our night vision plays into this as well.

 

Your thoughts?

 

Pete

 

 

[RLK1]

Some folks in the eyepiece forum on the plossl, orthos  versus Brandon oculars have mentioned using a light blue filter , I'm guessing written 80a?, as the galaxies as a r3sult appear plainer. These are seasoned  respectable observers so I take it seriously.  Here's what I'm guessing....

 

The pale blue serves to suppress the redder spectrums as in those orangey street lights and such.  You kno the common ones I'm talking about. I forget which is sodium vapor etc. etc..   Too some galaxies, younger still star forming associations would certainly *favor* a light blue filter.  We all kno as well, the blue/green sensitive area of our night vision plays into this as well.

 

Your thoughts?

 

Pete

I doubt such a filter will have any helpful outcomes on galaxy observations but there is one "blue" filter that may help with certain galaxies and it seems to function similar to a broadband LPR filter in this regard and that filter is a blue CCD imaging filter. 

 

I tried one after reading a forum post about it from J.Gardavsky and I'm glad that I did as it gave me one of the best views of the bearpaw galaxy I've ever seen in front of my moderately lighted polluted home with my 16" dob. 

 

Your experience with it may vary, of course, depending on light pollution levels, aperture, viewing conditions, specific galaxies being observed, etc...

[Redbetter]

Some folks in the eyepiece forum on the plossl, orthos  versus Brandon oculars have mentioned using a light blue filter , I'm guessing written 80a?, as the galaxies as a r3sult appear plainer. These are seasoned  respectable observers so I take it seriously.  Here's what I'm guessing....

 

The pale blue serves to suppress the redder spectrums as in those orangey street lights and such.  You kno the common ones I'm talking about. I forget which is sodium vapor etc. etc..   Too some galaxies, younger still star forming associations would certainly *favor* a light blue filter.  We all kno as well, the blue/green sensitive area of our night vision plays into this as well.

 

Your thoughts?

 

Pete

 

I would expect the opposite to be true for several reasons:

• Lighting/streetlights have shifted more to LED so the spectrum of light pollution is bluer now than it was before.
• Blue scatters more than the longer wavelengths.  This is not a plus...
• Galaxies on average are brighter on the redder end than on the blue.  Certainly this is true of the central bulges which are full of old stars redder than the Sun.

About the only place where filtering for blue would seem to offer an advantage is for the active star forming regions in the arms of active galaxies and such.

 

I have used yellow filters to specifically filter out the blue when looking at low surface brightness galaxies with heavy Milky Way dust extinction.

[j.gardavsky]

There is truth in the Redbetter's post.

 

Alternatively to the Baader blue(RGB)CCD (400nm - 500nm) interference filter, and to the Zeiss short pass (385nm - 490nm) blue interference filter,

I am using the long pass yellow filters to increase the visibility of the galaxies' cores an of the dark lanes around.

 

All these filters are mounted on the filter wheel.

As a rule, one of these filters work, if not, then there is still the "empty hole" on the filter wheel.

 

Clear skies,

JG

[saemark30]

The Lumicon Deep Sky filter may help with seeing some galaxies as suggested in their brochure. It has a  cyan color effect I find.

Edited by saemark30, 27 March 2025 - 11:10 AM.

[CrazyPanda]

The Lumicon Deep Sky filter may help with seeing some galaxies as suggested in their brochure. It has a  cyan color effect I find.

Here's the graph.

 

 

Looks like it clobbers sodium and mercury vapor lighting. So if you live in an area with sodium and mercury vapor lighting, then in theory this filter would suppress disproportionately more light pollution and air glow than light from the galaxy.

 

But if you live in an area with broad spectrum LED lighting, this filter will probably do more harm than good for the reasons Redbetter mentioned.

Edited by CrazyPanda, 28 March 2025 - 02:04 PM.

[RLK1]

Here's the graph.

 

 

Looks like it clobbers sodium and mercury vapor lighting. So if you live in an area with sodium and mercury vapor lighting, then in theory this filter would suppress disproportionately more light pollution and air clow than light from the galaxy.

 

But if you live an area with broad spectrum LED lighting, this filter will probably do more harm than good for the reasons Redbetter mentioned.

Of course it does depend, in part, on the type of light pollution present, but even IDA dark sky approved LED street lighting can still be mitigated by a filter and that's why I use a broadband UHC for most of my galaxy observations in front of my moderately light polluted home with the aforementioned lighting in place:

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[ButterFly]

Having a hole in a slider with other filters is the best way to find out. Spiral arms benefit the most for blue galaxy viewing. Remember that all filters work by taking away light, so there are tradeoffs. Broadband light pollution still leaves a lot of light in pretty much any band.

[j.gardavsky]

Having a hole in a slider with other filters is the best way to find out. Spiral arms benefit the most for blue galaxy viewing. Remember that all filters work by taking away light, so there are tradeoffs. Broadband light pollution still leaves a lot of light in pretty much any band.

Hole in one, filters in the others, 

that's my rule.

 

Thank you for your reply,

JG