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Equipment Discussions >> Eyepieces

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gregory93
super member


Reged: 07/03/12

Next filter recommendations new
      #5995333 - 07/28/13 07:13 PM

Hello fellow members.

As the title states i would like to have some recommendations on my next filter.I currently own a Baader UHC-S but i do not like it at all.It does not provide a great boost making the search of small planetaries and other nebulae rather impossible. I was thinking of getting a true UHC like the Orion UltraBlock or a Lumicon OIII.I am leaning slightly more towards the Ultrablock because i could use it in more objects,incl. the pns.

Any ideas?

Edit: i own a XT8.
Clear skies!

Edited by gregory93 (07/28/13 07:22 PM)


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Mariner@sg
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Reged: 06/28/12

Loc: Little Red Dot
Re: Next filter recommendations new [Re: gregory93]
      #5995568 - 07/28/13 09:41 PM

I'd recommend that you get either the Lumicon UHC, DGM NPB or the Orion Ultrablock to replace the UHC-S. From what I recall, the UHC-S is more for imaging than visual.

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AstroTatDad
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Reged: 04/22/13

Loc: Los Angeles - San Diego
Re: Next filter recommendations new [Re: Mariner@sg]
      #5995899 - 07/29/13 01:42 AM

The Orion Ultrablock is pretty close to Lumicon UHC. I prefer the Lumicon UHC. If you want to save a little money you can go for the DGM NPB and a good Oxygen III like the Lumicon OIII filter. The thousand oaks filters are good too, I'm very happy with my Lumicon filters.
I own the Lumicon UHC and OIII both awesome filters.

Check out David Knisely's on Filter Performance Comparisons For Some Common Nebulae, so you can get an idea what filters work on a big list of common Nebulae.
http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performa...

Edited by AstroTatDad (07/29/13 01:46 AM)


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gregory93
super member


Reged: 07/03/12

Re: Next filter recommendations new [Re: AstroTatDad]
      #5996018 - 07/29/13 06:49 AM

Thank you guys for your replies!
I have read that article many times in the past, that's why i want now to get a real filter.
Between DGM Npb and lumicon UHC which should provide a greater boost?Or is the difference so small you cannot tell?

Clear skies!


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Next filter recommendations new [Re: gregory93]
      #5996054 - 07/29/13 07:44 AM

Quote:

Thank you guys for your replies!
I have read that article many times in the past, that's why i want now to get a real filter.
Between DGM Npb and lumicon UHC which should provide a greater boost?Or is the difference so small you cannot tell?

Clear skies!




It is a fairly small difference. I find a *very* slight edge in contrast when using the NPB over the Lumicon UHC, but it takes a lot of study to see that difference. The NPB also produces a slightly more "color neutral" view rather than the more greenish hues seen in filters like the UHC or Orion Ultrablock. In any event, you can buy on price here and still get a good narrow-band nebula filter. Clear skies to you.


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AstroTatDad
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Reged: 04/22/13

Loc: Los Angeles - San Diego
Re: Next filter recommendations new [Re: gregory93]
      #5996066 - 07/29/13 07:58 AM

They are a "little" different, I have not used a DGM NPB as of yet. But it is a awesome filter used by many. Nice combo with a good Oxygen III filter such as the Lumicon. You can't go wrong with either or, Lumicon UHC or the NPB. If I was to start over I may have went for the NPB filter first. It just seems like a nice combo type filter.

The NPB (Narrow Pass Band) filter is an Ultra High Contrast type of filter that is very effective for small and fainter emission and planetary nebula and a variety of bright nebula, especially through larger scopes. Another nice feature of the NPB filter is the very natural coloration yielded by this UHC type filter. Star images retain a much more natural color, in addition to pinpoint star images. High transmission at the 656.3nm Hydrogen Alpha emission line is a bonus for this design.

Specifications

This DGM Optics custom designed filter is well suited for a variety of telescopes and objects. The filter design stresses maximum optical throughput utilizing state-of-the-art optical thin-film designs and materials.
This filter is a “first surface” hard oxide thin-film and is much more durable and long lived than laminated “soft film” designs used by several famous makers. They are also much less prone to the internal reflectance problems that plague laminated filters. Laminated filters can produce a very undesirable “doubling” of stellar images often with one of the doubles being red. Contrary to popular belief, this image doubling is not due to the red sideband component that many nebula filter designs produce, but in many cases is due to laminated glass not being exactly parallel to the protective cover plate after lamination. Many laminated filters display this annoying characteristic.
This filter averages around 1% transmission (optical density of 2) through the rejection region from 540 to 590nm, and average transmission greater than 90% in the passband, and greater than 75% at the 656.3nm H-Alpha line. The design yields a filter with a very symmetrical shape and high optical throughput, for maximum enhancement of nebula with a minimum of loss of stars in the field of view.
The substrate is B-270 and has measured total wavefront values of .25 waves. The combination of first surface optical thin-film technology and a polished, flat substrate enables this filter to be used with high magnification, a real plus for small planetary nebula.

Lumicon UHC
The ULTIMATE nebula filter. The Ultra High Contrast Filter is unbeatable for revealing nebulosity. This is achieved by passing three nebula emission lines-the two doubly ionized oxygen lines (496 and 501nm) and the H-beta line (486nm)-while blocking light-pollution and Sky Glow. The result is superb views of the Orion, Lagoon, Swan and other extended nebulae. Recommended for telescopes 8" and larger in aperture.

Edited by AstroTatDad (07/29/13 08:17 AM)


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Next filter recommendations new [Re: AstroTatDad]
      #5996659 - 07/29/13 01:52 PM

AstroTatDad wrote:

Quote:

The ULTIMATE nebula filter. The Ultra High Contrast Filter is unbeatable for revealing nebulosity.




Well, not quite. There are a number of emission nebulae which are better seen in some line filters rather than in a narrow-band nebula filter like the Lumicon UHC. In fact, there are a few objects that I have *only* seen in a line filter like the Lumicon OIII, so while the UHC is a good filter, it sometimes is not the filter of choice for a given nebula. Clear skies to you.


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AstroTatDad
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Reged: 04/22/13

Loc: Los Angeles - San Diego
Re: Next filter recommendations new [Re: David Knisely]
      #5997134 - 07/29/13 06:48 PM

Quote:

AstroTatDad wrote:

Quote:

The ULTIMATE nebula filter. The Ultra High Contrast Filter is unbeatable for revealing nebulosity.




Well, not quite. There are a number of emission nebulae which are better seen in some line filters rather than in a narrow-band nebula filter like the Lumicon UHC. In fact, there are a few objects that I have *only* seen in a line filter like the Lumicon OIII, so while the UHC is a good filter, it sometimes is not the filter of choice for a given nebula. Clear skies to you.




Yes very true David, I just put up the description from Lumicon and DGM. I was going to delete that part out, I guess I should have. LOL
And I know this because in my personal preference my OIII filter is my "Ultimate" filter. Only because of my favorite nebula's I like to observe the OIII works best on those. The way they have it in there description made me want to run to jack in the box and get a Ultimate Cheeseburger, not a filter LOL.

But really I enjoy using both my filters, still need to get the DGM Optics NPB and a H beta filter.


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BRCoz
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Reged: 10/21/05

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Re: Next filter recommendations new [Re: AstroTatDad]
      #5997352 - 07/29/13 09:47 PM

I use the Astronomik UHC, Orion OIII and Orion SkyGlow filters with low power.

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Alein 1630
super member


Reged: 01/18/13

Loc: Dutchess Count,y NY
Re: Next filter recommendations new [Re: gregory93]
      #5997487 - 07/29/13 11:12 PM

IIs there a waiting list for the npb? If so how long?

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AstroTatDad
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Reged: 04/22/13

Loc: Los Angeles - San Diego
Re: Next filter recommendations new [Re: Alein 1630]
      #5997544 - 07/29/13 11:42 PM

Quote:

IIs there a waiting list for the npb? If so how long?




I haven't checked in a while but they can also be bought from here
2" DGM NPB http://item.mobileweb.ebay.com/viewitem?sbk=1&nav=SEARCH&itemId=31070...

1.25" DGM NPB http://item.mobileweb.ebay.com/viewitem?sbk=1&nav=SEARCH&itemId=16104...

Edited by AstroTatDad (07/29/13 11:43 PM)


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Lamb0
Carpal Tunnel
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Reged: 07/25/07

Loc: South Eastern(ish) Nebraska
Re: Next filter recommendations new [Re: Alein 1630]
      #5997565 - 07/29/13 11:55 PM

I recommend the $150 2" NPB version where feasible. It currently shows "More than 10 available". You'll get a full 2° TFoV filtered (1.4° or 1.05° Barlowed, 2.1° TFoV unfiltered) when threaded into your 36mm Hyperion Aspheric, or ~1.7° in the 30mm Superview when used in your 8" Apertura AD8 without using your 2" Barlow. Typically, ~10x/" (30mm Superview fully Barlowed for 80x), is the normal maximum when used as a nebula filter... OTOH, try pointing more magnification at planets for a bit of fun!

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Alein 1630
super member


Reged: 01/18/13

Loc: Dutchess Count,y NY
Re: Next filter recommendations new [Re: Lamb0]
      #6009418 - 08/06/13 12:54 PM

Thanks! You also did all the math for mee too

Now, how would the thousands oak LP-2 compareto the NPB


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Next filter recommendations new [Re: Alein 1630]
      #6018117 - 08/10/13 07:12 PM

Quote:

Thanks! You also did all the math for mee too

Now, how would the thousands oak LP-2 compareto the NPB




They are quite similar, although I still might give a small nod to the NPB. Clear skies to you.


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gregory93
super member


Reged: 07/03/12

Re: Next filter recommendations new [Re: David Knisely]
      #6041327 - 08/23/13 07:12 AM

I just purchased one 1.25" NPB DGM filter.Should be here in about 2 weeks.

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REC
Post Laureate
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Reged: 10/20/10

Loc: NC
Re: Next filter recommendations new [Re: gregory93]
      #6041360 - 08/23/13 07:55 AM

I just ordered the 2" NPB on Monday and received it yesterday, great service.....only negative is, instead of packing it with foam, he used clouds!

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MrJones
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Reged: 09/15/10

Loc: Indiana
Re: Next filter recommendations new [Re: REC]
      #6041605 - 08/23/13 10:36 AM Attachment (18 downloads)

I have a problem with the continued recommendation of the DGM NPB filter and I'll explain why. First a brief review of what we're trying to do with a nebula filter.

Part I

The emission spectrum of Eta Carinae (thanks atlasoftheuniverse.com) is pretty typical for emission nebulae showing a mix of OIII and Ha, Hb peaks and other minor components.

A normal dark adjusted eye is most sensitive to blue-green light and insensitive to red light. To increase the contrast of nebulae for visual observation then an obvious path is to have a filter that selectively passes light just in the blue-green region around the OIII and Hb peaks and reflects everything else. This will reduce all extraneous light including that from stars through such a filter. These filters also reduce what you see of the nebulae as there are no 100% transmission filters. We will optimistically estimate that 90% transmission of the total area of interest is the best we can do. So if a nebula is beyond the threshold of detection and you add a nebula filter, you will have reduced it's brightness 10% through the filter and even with the improved background still won't see it.

Some of these filters also pass the red Ha region. This can be useful for two reasons. 1) This is often the strongest emission region of a nebula, so although the dark adjusted eye is fairly insensitive at this frequency, adding this information is only going to increase contrast. 2) You can also use these filters for one shot color astrophotography to capture all of the intense parts of most nebulae with significant contrast gain.

Note that I said "peaks" and not "lines". Due to the Heisenberg Uncertainty Principle and a few other factors the emission profiles centered at each frequency have a finite distribution and it's important to keep in mind that there is a lot of area in the bases of these peaks. So you don't actually want sharp cutoffs right at the frequencies of interest, but instead a cutoff range that encompasses most of the peaks with bases.

Finally we have recommendations for filters based on single observing reports. Perception is a funny thing. Been to a magic show? Ever read multiple police reports from the same incident? When trying to distinguish contrast differences of very similar views you are as likely to be right as wrong not even factoring in that everyone's vision itself is going to be different. The ONLY way to do this visually is to make a number of double blind observations with multiple observers, and determine if you have a statistically significant result.

Fortunately, unlike eyepieces for example, optical filters are not complex devices in practice. They pass some light and reflect some light. We can therefore make a number of determinations from just transmission spectra of the filters.

Part II (Some Filters Compared) will be coming soon ...


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MrJones
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Reged: 09/15/10

Loc: Indiana
Re: Next filter recommendations new [Re: MrJones]
      #6041883 - 08/23/13 01:22 PM

Part II

You may have caught Jim Thompson's filter data and reviews. He has recently posted a few things on these forums. While it would be ideal to specifically have a visual guide (Jim is primarily a video astronomer) and more information such as my post above to guide new people, he has compiled a lot of current filter data and this is what should be spammed in these forums vs. single observer subjective opinions and recommendations.

Two of his complete guides with data are here and here.

A comparison of specifically narrow band nebula filters, which should be your first and possibly only filter as an amateur astronomer is here.

Remember that we only want the light around the OIII and Hb lines and possibly Ha. You can immediately see from these transmittance profiles that the DGM NBP filter has a huge problem with transmitting a significant amount of spurious red and orange light outside these regions vs. the others. A tipoff should be that this filter transmits so much red and orange light that it actually appears red when you look through it. Not what we want at all. The one useful snippet of information from Knisley's guide is that this gives a more natural appearance. It does indeed as it lets through a lot more starlight, I have the Meade and Ultrablock filter in this comparison and the Meade does the same, probably to a much lesser degree, while the Ultrablock transmits no red and tints things including stars blue-green though the nebulae themselves look fine. Unfortunately the spurious light that the DGM lets through includes regions such as Na lamp emissions. While at very dark sites you may not notice much difference with other filters, in general this extra light well into the spectrum of what dark adjusted eyes can see is exactly what you are trying to avoid, will only cost you contrast, and in fact makes it obviously the WORST choice of these filters for most amateur astronomers, whether they be visual, video or photographic. As you can see in Jim's other filter comparisons the DGM filters all seem to have this problem.

Also looking at this chart you can see Lumicon with the highest overall transmittance for the OIII_Hb region which is exactly what I would expect from the most expensive filter, the Ultrablock with the (second) lowest transmittance in this region which is probably enough to be noticeable vs. at least the Lumicon and the rest with decent OIII/Hb and Ha regions.

Happy filter hunting and please everyone keep posting Jim Thompson's guides to educate and inform. And thank you Jim, keep up the good work.


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Next filter recommendations new [Re: MrJones]
      #6041959 - 08/23/13 02:18 PM Attachment (14 downloads)

Mr. Jones posted:

Quote:

A normal dark adjusted eye is most sensitive to blue-green light and insensitive to red light. To increase the contrast of nebulae for visual observation then an obvious path is to have a filter that selectively passes light just in the blue-green region around the OIII and Hb peaks and reflects everything else. This will reduce all extraneous light including that from stars through such a filter. These filters also reduce what you see of the nebulae as there are no 100% transmission filters. We will optimistically estimate that 90% transmission of the total area of interest is the best we can do. So if a nebula is beyond the threshold of detection and you add a nebula filter, you will have reduced it's brightness 10% through the filter and even with the improved background still won't see it.




The best AAVSO visual observers can, with a lot of repeated estimates and averaging, get a magnitude of a star to at best within +/- 0.1 stellar magnitudes (+/- 0.2 magnitudes is somewhat more common a magnitude error estimate). 0.1 magnitudes is a light intensity difference of 9.6% while 0.2 stellar magnitudes is a difference of 20% in light intensity. This means that for most observers, it is highly unlikely that the viewer could ever detect a difference in intensity of around 10% or less on diffuse objects like nebulae (and even a 15% to 20% difference might not be all that easy to see). The transmission of the OIII and H-Beta lines in the DGM NPB filter usually exceeds 90% (mine is closer to 93% at the OIII lines and 94% at H-Beta). Thus, the insertion line loss of the filter is basically undetectable visually. This also goes for the other good narrow-band nebula filters like the Lumicon UHC, Thousand Oaks Narrowband LP-2, and a few others that all have transmissions around 90% or more at the OIII and H-Beta line wavelengths. Any alleged light "loss" from the filters would be insignificant, and would be *more* than compensated for by the increase in contrast provided by the filter. In fact, as many of the more experienced deep-sky observers will tell you, there are a number of very very faint emission nebulae that are *only* readily visible with the proper narrow-band or line nebula filter.

Quote:

Note that I said "peaks" and not "lines". Due to the Heisenberg Uncertainty Principle and a few other factors the emission profiles centered at each frequency have a finite distribution and it's important to keep in mind that there is a lot of area in the bases of these peaks. So you don't actually want sharp cutoffs right at the frequencies of interest, but instead a cutoff range that encompasses most of the peaks with bases.




The Heisenberg uncertainty principle does not really come into this much here. The main problems are getting the passband in precisely the right wavelength location and sharpness on a repeatable basis, and that is a manufacturing issue. It would be difficult to get a filter narrow and sharp enough to have the uncertainty principle be a significant factor, as can be seen with etalon-based solar H-alpha filters that have passband widths well under one angstrom wide. With nebula filters, the passband can be considerably wider and can let through the wavelengths between the OIII and H-Beta lines without impacting the view significantly. In fact, you *want* the passband to be a little wider because for some shorter/ratio instruments (f/4 and faster), the angles that the light comes into the filter can be somewhat steeper, resulting in a shift in the filter's "skirts". For that reason (and the easier manufacturing), filters are not generally made for amateur use that have super-narrow passband widths with almost "square-wave" skirts. A good range for narrow-band filters is a FWHM figure in the 220 angstrom to 280 angstrom range with a peak transmission exceeding 90%.

Quote:

Finally we have recommendations for filters based on single observing reports. Perception is a funny thing. Been to a magic show? Ever read multiple police reports from the same incident? When trying to distinguish contrast differences of very similar views you are as likely to be right as wrong not even factoring in that everyone's vision itself is going to be different. The ONLY way to do this visually is to make a number of double blind observations with multiple observers, and determine if you have a statistically significant result.




These are not "single observing reports"! There are multiple ones, which can easily be accessed by viewing the postings on the Deep-sky forum, as well as in some web sites (Doug Snyder's PLANETARY NEBULAE OBSERVER'S HOME PAGE for example, which has hundreds of observing reports using filters). Also, you will find many reports on the more prominent deep-sky observer e-mail lists like the Yahoo AMASTRO list (that one has some of the best visual deep-sky observers on the planet there). On that AMASTRO group in particular, many observers use the DGM Optics NPB filter and report very good results. Many observers often say that they like the NPB notably better than the Lumicon UHC, although personally, I feel that the two filters are fairly similar (with a slight nod to the NPB overall). In my side-by-side tests using my Lumicon multi-filter selector, the NPB provided just a hair more contrast than the UHC did, although again, the difference wasn't exactly huge. I didn't use the NPB for my extended nebula/filter survey project, but with its characteristics, using it might have changed the results a little, at least on some objects.

Quote:

Remember that we only want the light around the OIII and Hb lines and possibly Ha. You can immediately see from these transmittance profiles that the DGM NBP filter has a huge problem with transmitting a significant amount of spurious red and orange light outside these regions vs. the others. A tipoff should be that this filter transmits so much red and orange light that it actually appears red when you look through it. Not what we want at all. The one useful snippet of information from Knisley's guide is that this gives a more natural appearance. It does indeed as it lets through a lot more starlight, I have the Meade and Ultrablock filter in this comparison and the Meade does the same, probably to a much lesser degree, while the Ultrablock transmits no red and tints things including stars blue-green though the nebulae themselves look fine. Unfortunately the spurious light that the DGM lets through includes regions such as Na lamp emissions. While at very dark sites you may not notice much difference with other filters, in general this extra light well into the spectrum of what dark adjusted eyes can see is exactly what you are trying to avoid, will only cost you contrast, and in fact makes it obviously the WORST choice of these filters for most amateur astronomers, whether they be visual, video or photographic. As you can see in Jim's other filter comparisons the DGM filters all seem to have this problem.




The huge "High-pressure Sodium Monster" is significantly attenuated by the NPB filter to a degree that it does not have an overwhelming impact on the overall view, so the NPB is hardly even anywhere near the "worst" narrow-band nebula filter. As many have found through careful first-hand observational experience, it is indeed one of the better narrow-band nebula filters on the market today. There is some weak red from HP Sodium that does get into that red secondary passband of the NPB, but there is also some blue-green from HP Sodium that also gets into the primary passbands of *all* of the narrow-band nebula filters. That is a significantly greater problem (and is another reason to have a good narrow OIII filter under some light pollution). Below is a rough depiction of the strength of the urban skyglow and the contributing species (along with the continuum of incandescent lighting). That gives one an idea of the problem even filtered viewing is likely to have under urban viewing conditions.

Clear skies to you.


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Next filter recommendations [Re: David Knisely]
      #6042182 - 08/23/13 04:36 PM

I've been experimenting with a lot of different filters recently: Lumicon, Thousand Oaks, Baader, TeleVue, and some Sirius Optics (now gone) filters.
Some have a red transmission, some don't. All have been compared under dark skies, so I cannot safely extrapolate what I see to their usage in brighter environments. That is a key point, since they may perform differently in an urban or suburban environment.

But, the only negative I have about the filters with some deep red transmission is that the star images appear to be a blue-green color with a trace of red "fuzz" around them. Otherwise, I saw no negative aspects to the red transmission.

In fact, two nebulae in particular, M42 and M8, displayed some interesting deep red colors in the nebulae when used with a filter transmitting the deep red (i.e. Ha), while filters that had no deep red transmission (e.g. Orion UltraBlock) took away that aspect of the nebulae. And frankly, I missed the red details.

Since my environment was quite dark, I didn't mind the filters with the slightly-too-wide bandwidths because the starfields appeared more normal. Perhaps the nebulae didn't display the ultimate in details, but the beauty of the field made up for it. I noticed this a lot on objects like the Crescent Nebula (NGC6888) and Thor's Helmet, where a reduction in nebula prominence was OK when the rich fields were better filled with stars. On both of those, I liked the aesthetic view using the too-wide TeleVue O-III better than the Lumicon O-III, my reference standard.

But, I will grant that if the desire is to enhance the nebula the most, having a narrower filter will help more. For me, the jury is still out on the Baader O-III, which is a little too narrow (cuts a lot of the 496nm transmission), yet does great on some planetaries with most of their transmission energies at 501nm.

So, one could argue that different filters make sense for different objects, and that different bandwidths may make sense based on observing conditions, scope size, and aesthetic considerations.

Is there any general conclusion to take away? Yes, you want the filter to transmit the wavelengths you want to see at better than 90%, yet transmit no other wavelengths. Is there value in seeing the deep red at 656nm (Ha)? Yes there is, but not, perhaps, on every object.

Maybe the industry should come up with descriptive standards, such as:
5) Broadband: notches out some of the most prevalent light pollution lines but has otherwise little effect.
Enhancement: Light.

4) Wide Nebula filter: Like a UHC only closer to a broadband. A nice filter for big scopes, aesthetic considerations, or small scopes to keep the fields brighter. Generally more useful than a broadband. Enhancement: Medium

3) Narrowband (UHC) filters: transmits the prominent nebula lines (with red yes or no). The best contrast enhancement for general use on nebulae.
Enhancement: Strong

2) Line filters (O-III, Hb for Visual): the narrowest bandwidth to pass as close as possible to ONLY specific wavelengths.
Enhancement: Maximum

1) Line filters (Imaging): the minimum bandwidth necessary to pass a single line in the spectrum. Too narrow, perhaps, for visual use--specialized for photographing at wavelengths unimportant to visual use or to see specific emission wavelengths.
Enhancement: Ultimate.

Just a suggestion......


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