Filters for various things

[russmax]

I'm pondering eyepiece filters. I have Celestron's box o' Plossls and filters, but the only filter I ever use is the neutral density moon filter. A green-tinted moon filter came included with some accessory I ordered, but I hate it. I'm pondering a 4-filter set from Celestron that has 3 neutral density moon filters with different light transmission, and a "Moon & Skyglow" filter, all for $40.
https://www.highpointscientific.com/cel ... inch-94315

What filters for viewing have people found useful for various celestial objects?

Best regards,
Russmax

[Lady Fraktor]

The Baader M&S is a useful filter for lunar and planets, Baader Contrast Booster, and the Baader Solar Continuum are all excellent.
The ND filters are handy but good ones like the B+W are more expensive but do a better job than these ND filters.
The best way to view the Moon or planets without using ND filters or polarizers is to not let your eyes become dark adapted.

[Refractordude]

This filter is less expensive and does the same thing. The image is a review of the filter. Right click the image.

[bladekeeper]

An OIII filter and a narrowband UHC filter are quite handy for nebulae and planetary nebulae. A lot of folks enjoy the DGM NPB filter as the UHC option.

[russmax]

Thanks for the input, everyone. I did not buy the Celestron Moon filter kit. You all saved me from spending money on junk.

Now I'm researching the filters that everyone mentioned. I can see how the Baader filters are worth the money, and how lesser filters will degrade my views.

• Baader Moon & Sky: This seems like what I had in mind
• Baader Contrast Booster: This looks like the M&S without the IR/UV blocker.
• Baader Solar Continuum: I don't do any solar astronomy. Don't intend to until the solar eclipses coming up in 2023/2024.
• Baader Fringe Killer or Semi-APO filter might also be useful in my f/6.5 refractor.
• Baader OIII

Some of those are variations and combinations of each other, so I will have a hard time picking one or two.

A variable polarizer would be useful, but is not what I have in mind, right now. I like the repeatability of fixed ND filters.

OIII and narrowband UHC filters would also be useful for enhancing my deep sky viewing.

I think my next astronomy purchases will be these filters, in this order:

1. Baader Moon & Sky
2. DGM NPB (UHC filter)
   
   Thanks, and Clear Skies,
   Russmax

[Lady Fraktor]

The solar continuum filter pulls out detail on planetary and lunar as well, it is not just for solar. It is tuned to the eyes visual range.
The M&S + Baader Fringe Killer is almost the same as a Semi Apo filter using them combined led to the development of the SA filter.

[russmax]

In my research, I found this old article very helpful:
http://www.astronomy.com/~/media/import ... ilters.pdf

An oldie, but a goodie, I think.

[Lady Fraktor]

Exit pupil is important when viewing with filters as well though very, very few of the articles ever even mention it.

[LDW47]

Thanks for the input, everyone. I did not buy the Celestron Moon filter kit. You all saved me from spending money on junk.

Now I'm researching the filters that everyone mentioned. I can see how the Baader filters are worth the money, and how lesser filters will degrade my views.

• Baader Moon & Sky: This seems like what I had in mind
• Baader Contrast Booster: This looks like the M&S without the IR/UV blocker.
• Baader Solar Continuum: I don't do any solar astronomy. Don't intend to until the solar eclipses coming up in 2023/2024.
• Baader Fringe Killer or Semi-APO filter might also be useful in my f/6.5 refractor.
• Baader OIII

Some of those are variations and combinations of each other, so I will have a hard time picking one or two.

A variable polarizer would be useful, but is not what I have in mind, right now. I like the repeatability of fixed ND filters.

OIII and narrowband UHC filters would also be useful for enhancing my deep sky viewing.

I think my next astronomy purchases will be these filters, in this order:

1. Baader Moon & Sky
2. DGM NPB (UHC filter)
   
   Thanks, and Clear Skies,
   Russmax

If you want to view the Orion, Lagoon etc. nebulas in all their glory I would get the NPB first, don’t you already have a moon filter or two, unless one will follow the other rather quickly !

[Baurice]

A FULL APERTURE solar filter is great, as long as there are sunspots to see.

A light pollution reduction filter helps on some deep sky objects but not all. It is great for galaxies and nebulae and not so much for open star clusters.

The best of all are solar narrowband filters but these are expensive and highly addictive.

[Bigzmey]

Thanks for the input, everyone. I did not buy the Celestron Moon filter kit. You all saved me from spending money on junk.

Now I'm researching the filters that everyone mentioned. I can see how the Baader filters are worth the money, and how lesser filters will degrade my views.

• Baader Moon & Sky: This seems like what I had in mind
• Baader Contrast Booster: This looks like the M&S without the IR/UV blocker.
• Baader Solar Continuum: I don't do any solar astronomy. Don't intend to until the solar eclipses coming up in 2023/2024.
• Baader Fringe Killer or Semi-APO filter might also be useful in my f/6.5 refractor.
• Baader OIII

Some of those are variations and combinations of each other, so I will have a hard time picking one or two.

A variable polarizer would be useful, but is not what I have in mind, right now. I like the repeatability of fixed ND filters.

OIII and narrowband UHC filters would also be useful for enhancing my deep sky viewing.

I think my next astronomy purchases will be these filters, in this order:

1. Baader Moon & Sky
2. DGM NPB (UHC filter)
   
   Thanks, and Clear Skies,
   Russmax

Baader Moon & Sky Glow is a nice filter to have. It serves dual purpose: 1) a broadband light pollution filter. It helped me on quite few occasions to pull galaxies, globes and comets from light domes in the sky, 2) planetary filter. To improve contrast and cut glow without affecting planetary colors.

For nebulae UHC filter is a good starting point, but I would suggest to go with Lumicon, Astronomik or Orion Ultrablock over NPB. Lumicon and Astronomik are top tier UHC filters and would last you for life. New 1.25" Lumicon is ~$100 and new NPB is ~$75. In this case extra $25 is well spent. Lumicon provides report for each filter, so you see what you get. They have highest levels of transmittance (90-99%) in H-beta and OIII bands. Astronomik is very close in performance, but they don't provide reports for individual filters.

Orion Ultrablock and DGM NPB are second tier UHC filters. They are solid performers but typically somewhat under-perform compared to the top tier. Orion Ultrablock spectrum shape comes close to Lumicon, but it transmits a bit less light, typically in 85-90% range in both H-beta and OIII. DGM NPB transmits 85-90% in OIII bands, but cuts to aggressively into H-beta (only 68% transmittance in the sample I had). Since they cost about the same I recommend Orion over DGM.

[kt4hx]

I would also put in a good word for the DGM NPB filter. It is a narrow-band nebula filter that also does a good job in the O-III line and thus works nicely with many planetary nebulae.

As Gabrielle mentioned, exit pupil is an important factor and can impact filter choice. For instance, at higher magnification (smaller exit pupil) which darkens the field, a filter of wider passband can be beneficial because it allows more light through to the eye. Whereas as lower magnification (larger exit pupil) with a wider and brighter field, a filter with a tighter bandwidth would be preferable. For that reason some folks like to have both a narrow and wider bandwidth version of both the nebula and O-III filters to accommodate various magnifications.

The so-called Light Pollution Reduction (LPR) filters, such as the Orion Sky Glow, Baader UHC-S, etc., are very wide broadbanded filters that have variable benefit for visual observers. Under extreme light pollution conditions they can become swamped by the brightness of the sky and rendered ineffective. From darker locations they can give a subtle contrast boost visually to galaxies and some nebulae. However, that boost is very subtle and many observers may not even perceive the benefit.

On the very rare occasion that I would look at the moon, I typically prefer no filter. But as Gabrielle mentioned you do not want to be dark adapted for that. I will look at a nearby light before I go to the eyepiece in order to constrict my pupil to decrease the shock of looking at it through the eyepiece.

[LDW47]

There is quite an extensive study by a respected member, I believe, that compares the specs / performance of a wide range of filters incl curve graphs for various objects ie nebulas ! Find it, peruse it and see where the NPB stands in the line up !

[LDW47]

I would also put in a good word for the DGM NPB filter. It is a narrow-band nebula filter that also does a good job in the O-III line and thus works nicely with many planetary nebulae.

As Gabrielle mentioned, exit pupil is an important factor and can impact filter choice. For instance, at higher magnification (smaller exit pupil) which darkens the field, a filter of wider passband can be beneficial because it allows more light through to the eye. Whereas as lower magnification (larger exit pupil) with a wider and brighter field, a filter with a tighter bandwidth would be preferable. For that reason some folks like to have both a narrow and wider bandwidth version of both the nebula and O-III filters to accommodate various magnifications.

The so-called Light Pollution Reduction (LPR) filters, such as the Orion Sky Glow, Baader UHC-S, etc., are very wide broadbanded filters that have variable benefit for visual observers. Under extreme light pollution conditions they can become swamped by the brightness of the sky and rendered ineffective. From darker locations they can give a subtle contrast boost visually to galaxies and some nebulae. However, that boost is very subtle and many observers may not even perceive the benefit.

On the very rare occasion that I would look at the moon, I typically prefer no filter. But as Gabrielle mentioned you do not want to be dark adapted for that. I will look at a nearby light before I go to the eyepiece in order to constrict my pupil to decrease the shock of looking at it through the eyepiece.

I have a Celestron UHC filter, made by Baader but less expensive, it performs well for what it is, it has its place, its uses when you want something not as dark as an NPB, Lumicon etc. !

[kt4hx]

I would also put in a good word for the DGM NPB filter. It is a narrow-band nebula filter that also does a good job in the O-III line and thus works nicely with many planetary nebulae.

As Gabrielle mentioned, exit pupil is an important factor and can impact filter choice. For instance, at higher magnification (smaller exit pupil) which darkens the field, a filter of wider passband can be beneficial because it allows more light through to the eye. Whereas as lower magnification (larger exit pupil) with a wider and brighter field, a filter with a tighter bandwidth would be preferable. For that reason some folks like to have both a narrow and wider bandwidth version of both the nebula and O-III filters to accommodate various magnifications.

The so-called Light Pollution Reduction (LPR) filters, such as the Orion Sky Glow, Baader UHC-S, etc., are very wide broadbanded filters that have variable benefit for visual observers. Under extreme light pollution conditions they can become swamped by the brightness of the sky and rendered ineffective. From darker locations they can give a subtle contrast boost visually to galaxies and some nebulae. However, that boost is very subtle and many observers may not even perceive the benefit.

On the very rare occasion that I would look at the moon, I typically prefer no filter. But as Gabrielle mentioned you do not want to be dark adapted for that. I will look at a nearby light before I go to the eyepiece in order to constrict my pupil to decrease the shock of looking at it through the eyepiece.

I have a Celestron UHC filter, made by Baader but less expensive, it performs well for what it is, it has its place, its uses when you want something not as dark as an NPB, Lumicon etc. !

It is true some folks are put off by the darkness of the tighter filters. I guess since I've used them enough through the years it doesn't bug me. Even used my Orion O-III with 15x70 binoculars once to pick up M97. More of an experiment than anything, but was interesting.

[LDW47]

I would also put in a good word for the DGM NPB filter. It is a narrow-band nebula filter that also does a good job in the O-III line and thus works nicely with many planetary nebulae.

As Gabrielle mentioned, exit pupil is an important factor and can impact filter choice. For instance, at higher magnification (smaller exit pupil) which darkens the field, a filter of wider passband can be beneficial because it allows more light through to the eye. Whereas as lower magnification (larger exit pupil) with a wider and brighter field, a filter with a tighter bandwidth would be preferable. For that reason some folks like to have both a narrow and wider bandwidth version of both the nebula and O-III filters to accommodate various magnifications.

The so-called Light Pollution Reduction (LPR) filters, such as the Orion Sky Glow, Baader UHC-S, etc., are very wide broadbanded filters that have variable benefit for visual observers. Under extreme light pollution conditions they can become swamped by the brightness of the sky and rendered ineffective. From darker locations they can give a subtle contrast boost visually to galaxies and some nebulae. However, that boost is very subtle and many observers may not even perceive the benefit.

On the very rare occasion that I would look at the moon, I typically prefer no filter. But as Gabrielle mentioned you do not want to be dark adapted for that. I will look at a nearby light before I go to the eyepiece in order to constrict my pupil to decrease the shock of looking at it through the eyepiece.

I have a Celestron UHC filter, made by Baader but less expensive, it performs well for what it is, it has its place, its uses when you want something not as dark as an NPB, Lumicon etc. !

It is true some folks are put off by the darkness of the tighter filters. I guess since I've used them enough through the years it doesn't bug me. Even used my Orion O-III with 15x70 binoculars once to pick up M97. More of an experiment than anything, but was interesting.

Its not that you are really put off with the darkness of the tighter filters its that the Celestron UHC gives you a different view that is a nice change from the darker sometimes, although I have 2 NPB’s as well. Its like everything else, a change is as good as a rest ! I also have a Tele Vue Bandmate OII that I like a lot so I mix and match and use different filters quite often, in both 1.25” and 2” sizes.

[kt4hx]

I have a Celestron UHC filter, made by Baader but less expensive, it performs well for what it is, it has its place, its uses when you want something not as dark as an NPB, Lumicon etc. !

It is true some folks are put off by the darkness of the tighter filters. I guess since I've used them enough through the years it doesn't bug me. Even used my Orion O-III with 15x70 binoculars once to pick up M97. More of an experiment than anything, but was interesting.

Its not that you are really put off with the darkness of the tighter filters its that the Celestron UHC gives you a different view that is a nice change from the darker sometimes. Its like everything else, a change is as good as a rest ! I also have a Tele Vue Bandmate OII that I like a lot so I mix and match and use different filters quite often, in both 1.25” and 2” sizes.

Truth be told I am not a prolific filter user anyway. I have the Orion Sky Glow, O-III, Ultra Block, the NPB and a Baader HaB. The majority of my time is spent pursing galaxies with the big scope at our dark site. But, I like to have the filters in the case in the event I decide to vary up my routine. Besides, I do love a good view of the Veil using the O-III.

[russmax]

Bigzmey,
You’ve quite correctly got the gist of what I’m after with the filters. Thanks for the Lumicon recommendation. I don’t think $25 is significantly more to pay for 99% vs 90% throughput in the passband.
—Russmax

Baader Moon & Sky Glow is a nice filter to have. It serves dual purpose: 1) a broadband light pollution filter. It helped me on quite few occasions to pull galaxies, globes and comets from light domes in the sky, 2) planetary filter. To improve contrast and cut glow without affecting planetary colors.

For nebulae UHC filter is a good starting point, but I would suggest to go with Lumicon, Astronomik or Orion Ultrablock over NPB. Lumicon and Astronomik are top tier UHC filters and would last you for life. New 1.25" Lumicon is ~$100 and new NPB is ~$75. In this case extra $25 is well spent. Lumicon provides report for each filter, so you see what you get. They have highest levels of transmittance (90-99%) in H-beta and OIII bands. Astronomik is very close in performance, but they don't provide reports for individual filters.

Orion Ultrablock and DGM NPB are second tier UHC filters. They are solid performers but typically somewhat under-perform compared to the top tier. Orion Ultrablock spectrum shape comes close to Lumicon, but it transmits a bit less light, typically in 85-90% range in both H-beta and OIII. DGM NPB transmits 85-90% in OIII bands, but cuts to aggressively into H-beta (only 68% transmittance in the sample I had). Since they cost about the same I recommend Orion over DGM.

[Ylem]

I use my OIII filter and a narrowband UHC filters the most. But honestly I don't use filters that much, YMMV

[TCampbell]

I think most of the major beneficial filters have been mentioned. No filter is great at everything, but some are handy for specific objects.

When I was new to astronomy I thought filters would really be a tremendous help. It turns out they are mildly helpful and take a bit of getting used to them. This is because all filters block light. But the trick is to try selectively block light. So they don't pull off any miracles to make the sky seem as if you don't live in a light polluted area. Also important is that if your eyes are around a bunch of outdoor lighting, your pupils will get not open up as much and, consequently, you wont see as much.

The OIII is probably the only true "narrowband" filter that I like. Only certain nebulae work well with this filter (emission nebulae rich in oxygen... the Omega nebula (aka "Swan") comes to mind.)

UHC filters are technically all "broadband". These work on the assumption that the source of light pollution is caused by either Mercury street lights or Sodium street lights. That used to be largely true ... but as cities convert over to LED lighting, the UHC filters are not as effective. They work by blocking the ranges of emission bands for sodium and mercury atoms but not blocking the other ranges (so these are broadband filters ... narrow band filters block *everything* except for a very narrow range of specific emission lines).

UHC filters can be somewhat aggressive ... and you may find that the whole image is just too dark to be enjoyed (filters only block light) and again... less effective in areas with LED street lights (LED lights are emitting light in loads of bands ... not just limited to the ranges of mercury or sodium lighting). I do not enjoy using UHC (UHC = Ultra High Contrast) filters for visual astronomy (but they do work well when imaging if you don't have a lot of LED lighting).

SOME filters are really designed for astrophotography because they are so aggressive that what you get out of them isn't going to be strong enough for your eye to see much ... but cameras doing long-exposure imaging are just fine. E.g. ... good luck seeing anything through a narrowband H-alpha filter.

So this is where the Baader "Moon & Sky Glow" filter comes in ... this is basically a very weak version of a UHC filter. It moderately filters the sources of light pollution but it tries to be gentle to the point the image isn't hopelessly too dark to enjoy. You get a little bit of an improvement ... not a miracle ... but it tries to make your visual observing better without being too aggressive.

Then there are the moon filters. The moon is so bright that if you observe it during the night, the next several objects you observe AFTER the moon will be hard to see because the moon basically destroys your eyes "dark adaptation". The moon filters basically just dim the moon. It wont look any sharper or have more contrast ... it just wont be so blindingly bright.

These moon filters come in strengths. I wish there was some standard ... but it turns out there are lots of standards. Sometimes they are labeled based on "optical density" factors. An optical density of 0.3 cuts the light transmission by 50%. An optical density of 0.6 cuts the light by 75%. This is because each 0.3 (do not ask me where they came up with the "0.3" standard... it makes no sense to me) cuts the light transmission by 1/2... by when you double that up to 0.6 it's really 1/2 of 1/2 (which is lets just 1/4 of the light through). If you had a 0.9 it would be 1/2 of 1/2 of 1/2 (or just 1/8th of the light comes through).

So sometimes you'll see moon filters labeled based on the percentage of light that can pass. The common versions are ND50 (50% of the light... basically that's an OD 0.3 filter) or ND25 (1/4 of the light comes through ... basically that's an OD 0.6) and ND13 (1/8th ... really a round of of 12.5% and that's equivalent to an OD 0.9).

BTW "OD" stands for "Optical Density" and "ND stands for "Neutral Density". Optical Density makes sense. The term "Neutral" in Neutral Density means it blocks all wavelengths of light equally (it doesn't block one part of the visible light spectrum more than any other part of the visible light spectrum). This means it's basically "sunglasses" for your telescope and the number after the letters "ND" is the percentage of light allowed to pass through the filter.

Alas there is also something called a "variable" neutral density filter for the moon. This is really either one single polarizer or two polarizing filters. If your telescope has any 45° mirror in it then a single polarizer does the trick. This is because when you bounce light off a 45° mirror (so the light takes a 90° turn) you "polarized" the light. If you then attach a "linear" polarizer to an eyepieces... you can simply rotate that eyepiece and it will brighten or dim the light. Basically one 45° mirror and one "linear" polarizer filter will behave the same as two linear polarizers stacked together. If you stack two linear polarizers together you can twist them and it will reduce or increase the amount of light transmitted. The general idea is it results in the ability to vary the brightness of the moon ... just by twisting the filter.

I usually try to save the moon to be the last thing I observe ... knowing that if it ruins my night vision it doesn't matter because I was about to pack everything up anyway.