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CN Report: Filter Performance Comparisons

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#1 asaint

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Posted 05 October 2006 - 10:06 AM

Filter Performance Comparisons

#2 reflector74

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Posted 05 October 2006 - 10:44 AM

I have some disagreements.

A prime example is what a terrific O-III can do for such planetaries as M27, M57, or M76 compared to the Lumicon UHC filter- also a fine filter. I greatly prefer the Baader O-III on those particular objects in my opinion. There are a great number of planetary nebulae in the heavens faintly visible in my 12" only with the use of an O-III filter.

Another thing I have found is that any object that my UHC filter enhances in a significant way will benefit in a unique and worthwhile way from my Lumicon H-beta filter! :) My Lumicon Swan Band comet filter also imparts really neat views of lots of nebulae.

Why were there no other brands of filters looked through for the article and why isn't Lumicon in the title?

#3 timmbottoni

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Posted 05 October 2006 - 12:55 PM

Thanks for this excellent update to the original, which I have linked many people to here...
http://pages.sbcglob...ash/filters.htm

I have an 80mm refractor, and under my light polluted skies, I have tried an Orion Skyglow and an Andover Tri-band, but I felt both weren't really a good investment for me, since I don't have enough light grasp, in my opinion, to really use these.

Any thoughts? Is there a minimum recommended aperture at which you think these filters become worthwhile?

Thanks,

Timm

#4 David Knisely

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Posted 05 October 2006 - 01:54 PM

I have some disagreements.

A prime example is what a terrific O-III can do for such planetaries as M27, M57, or M76 compared to the Lumicon UHC filter- also a fine filter. I greatly prefer the Baader O-III on those particular objects in my opinion. There are a great number of planetary nebulae in the heavens faintly visible in my 12" only with the use of an O-III filter.

Another thing I have found is that any object that my UHC filter enhances in a significant way will benefit in a unique and worthwhile way from my Lumicon H-beta filter! :) My Lumicon Swan Band comet filter also imparts really neat views of lots of nebulae.

Why were there no other brands of filters looked through for the article and why isn't Lumicon in the title?


This is a survey of nebulae to help indicate which "type" of filter (i.e. broadband, narrowband, or one of the two types of line filters) may be effective on a given object. As such, it is not a review of the various manufacturer's products, but is a guide to which type of filter might be more useful. Individual preferences (greatest brightness/nebulosity vs. greatest contrast) will tend to guide the obsever as to which filter they would choose for viewing a given object, which accounts for some of the variation in results. However, there are a number of objects which certain filters should *not* be used on, and I indicate that in the comments section. The H-Beta tended to be in this "not recommended" category a lot.

As I indicated in the text, the judgement of which filter was best was based on a number of factors which were all weighted together, rather than just on one. These factors include nebula brightness, the total area of nebulosity shown, and the relative contrast of the features visible within the nebula. The OIII as a general trend tended to provide somewhat more contrast (especially on many planetary nebulae), but the UHC generally showed a greater total area of nebulosity at a somewhat higher brightness level than the OIII. On M27, the object showed the largest area of nebulosity at the highest level of brightness with the UHC filter when compared to the OIII. This was particularly noticable on the faint outer "wings" of the nebula, which are much less prominent in the OIII. Under some moderate to severe light pollution, the OIII may have to be used over the UHC just to screen-out some of the light pollution a bit more effectively, but under mild skyglow to dark-sky conditions, the UHC was the clear winner. The H-Beta filter showed the nebula, but the outer wings were gone, and the dumbell form was not as large or as bright as in the other filters. A similar situation occurs with M76, although the OIII does provide a higher level of contrast as I noted in the detailed results. For M57, there is a very faint irregular outer shell around the object and this was best seen from a dark sky site with the UHC filter. While the OIII will give more contrast, the outer shells were more difficult to see than they were in the UHC filter. At higher powers (and to some extent, with some smaller apertures) a narrowband filter like the UHC may show a bit of an advantage over the OIII, although the OIII is still very useful, even in some rather small apertures.

As for why the Lumicon line was the only one used, the original limited survey was done many years ago when I only had the Lumicon set and the other company's filters were just coming into existance (the only company that had an OIII or H-Beta was Lumicon). In science, for proper repeatability and consistency, it is best to use the very same equipment that you started with when making an observation during an extended project, so that differences in results are not due to the differing equipment. Again, this is a nebula "survey" and not really a review article. I have tested a number of narrow-band and line filters, and the Lumicons tended to be the "gold standard" on which to compare (i.e. the UHC had greater than 90% transmission from 480nm to 510nm). The Meade Narrowband tended to have a passband which was almost identical to that of the UHC, while the Orion Ultrablock has a more "Gaussian" passband, with slight fall-offs in brightness on the blue and red sides of the central maximum. This gave a very slightly darker image than the UHC, although in practice, the Ultrablock and UHC yield a nearly identical degree of image enhancement. The Astronomik UHC also gives results which are very similar to that of the Lumicon UHC. The DGM Optics NPB has a primary passband that is slightly narrower than the Lumicon UHC, but which still takes in the OIII and H-Beta lines (as well as H-alpha, which generally isn't that important except with very large apertures). I like it slightly more than the Lumicon UHC, but again, the difference isn't exactly like night and day. As for the OIII's, the Thousand Oaks model again is quite similar to the early OIII's by Lumicon, except that, to avoid the red "ghosting" in star images caused by Lumicon's "red leak" passband, the Thousand Oaks Type III did not have any red transmission (the newer 2" Lumicon OIII's also no longer have any red transmission). The Tele Vue Bandmate OIII has a little too broad a passband to be considered a "true" OIII, so it does not provide quite the same level of contrast enhancement that the Lumicon and Astronomik OIII's tend to provide. With the H-Beta, again, the Astronomik model is fairly similar to my Lumicon H-Beta in overall performance. In most cases, once you get to 90% transmission and include the proper emission lines with steep passband skirts, the various manufacturer products perform in a very similar manner, especially when considering which "type" of filter (i.e. broadband vs. narrowband, vs. line) is best to use on a given object. Clear skies to you.

#5 Mr. Bill

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Posted 05 October 2006 - 02:34 PM

Good job, and thanks for what is obviously a "labor of love."

My personal observations agree in large part with your conclusions; UHC followed by OIII for the majority of views. In the end, it is as much an aesthetic judgement as objective as to the best filter for a particular object.

This is IMO why visual astronomy is so much fun.
;)

#6 spaceydee

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Posted 05 October 2006 - 03:11 PM

Wow, great article!

#7 LivingNDixie

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Posted 05 October 2006 - 03:20 PM

Nice write up David

#8 Glassthrower

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Posted 05 October 2006 - 04:14 PM

A print out of this article should be a standard reference for people considering filter usage.

Very thorough and well done David.

Clear dark skies...

MikeG

#9 Starman1

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Posted 05 October 2006 - 05:10 PM

A prime example is what a terrific O-III can do for such planetaries as M27, M57, or M76 compared to the Lumicon UHC filter- also a fine filter. I greatly prefer the Baader O-III on those particular objects in my opinion. There are a great number of planetary nebulae in the heavens faintly visible in my 12" only with the use of an O-III filter.


If I read the various German lab test reports correctly, the Baader O-III filter has a nice, narrow bandwidth and differs from the Lumicon only in the maximum percentage of transmission (slightly less, but still 90% or so). I wouldn't really expect there to be ANY visible difference between the two brands.

I agree in general that an O-III filter is desirable for most planetaries. I have not done the extensive research that David has done--I tend to use only one filter on each object according to the spectrum of light it emits--but I think a UHC does do a better job on M27 than an O-III.

Here's a wonderful site that shows the spectra of many nebulae in the sky:
http://oit.williams....ulae/browse.cfm

If the spectrum shows any appreciable H-Beta transmission, I'd use a UHC instead of an O-III. There are a few nebulae in here that show a strong H-Alpha transmission. On those, I'd recommend a filter with a strong H-Alpha transmission (whichever brand that might be). One can be quite methodical about the approach to which filter is best, but it may take a decent collection of many near-identical filters to do so.
I suppose some enterprising amateur astronomer with a large selection of filters might be able to give us as lengthy a list as the site I link to but with a recommended brand and type of filter for that object. Such a list would be relevant only so long as no manufacturer changed its filters, and, alas, that's not been the case in the past.

#10 Dave Chadsey

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Posted 05 October 2006 - 06:09 PM

Great job David. Thank you for all that work and an excellent write-up. :applause:

#11 dave b

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Posted 05 October 2006 - 08:11 PM

a guy once gave me an abridged version of your first article. he had put the filters in order of best for each object.

so if the UHC was best, it was listed first on the list under the object title. anything that scored 1 or zero was not listed at all.

thanks for the great article

#12 David Knisely

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Posted 05 October 2006 - 11:22 PM

Thanks for this excellent update to the original, which I have linked many people to here...
http://pages.sbcglob...ash/filters.htm

I have an 80mm refractor, and under my light polluted skies, I have tried an Orion Skyglow and an Andover Tri-band, but I felt both weren't really a good investment for me, since I don't have enough light grasp, in my opinion, to really use these.

Any thoughts? Is there a minimum recommended aperture at which you think these filters become worthwhile?

Thanks,

Timm


No, there is no minimum aperture for filter use, although the larger the telescope, the greater the number of objects that will be accessable which filters will tend to help. I would recommend either a DGM Optics NPB filter, a Lumicon UHC (or Astronomik's version), or the Orion Ultrablock. Here, you can buy on price. I like the NPB filter just a hair more than the UHC, but again, the difference is small. In fact, at times, the NPB filter has been a little cheaper than the UHC. Remember to use nebula filters at powers between about 3.5x per inch and 9.9x per inch of aperture, which for your 80mm scope, would be from 11x to 31x, and get as dark adapted as you can. Most of the improvement in the view comes from the fainter areas of nebulosity, so averted vision is a must here. Good luck and clear skies to you.

#13 ausastronomer

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Posted 05 October 2006 - 11:46 PM

Excellent work Dave,

I have referred to your original comparison on many occasions over the last few years and appreciate the update. On some targets that you prefer the UHC I prefer the OIII, but this is solely a matter of observer preference and on those targets I can appreciate why you prefer the UHC. I have the Astronomiks UHC and OIII filters in 1.25" version and the DGM NPB filter in 2" format. I am also very impressed with the performance of the DGM NPB filter.

CS-John B

#14 reflector74

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Posted 06 October 2006 - 03:48 AM

I have some disagreements.

A prime example is what a terrific O-III can do for such planetaries as M27, M57, or M76 compared to the Lumicon UHC filter- also a fine filter. I greatly prefer the Baader O-III on those particular objects in my opinion. There are a great number of planetary nebulae in the heavens faintly visible in my 12" only with the use of an O-III filter.

Another thing I have found is that any object that my UHC filter enhances in a significant way will benefit in a unique and worthwhile way from my Lumicon H-beta filter! :) My Lumicon Swan Band comet filter also imparts really neat views of lots of nebulae.

Why were there no other brands of filters looked through for the article and why isn't Lumicon in the title?


This is a survey of nebulae to help indicate which "type" of filter (i.e. broadband, narrowband, or one of the two types of line filters) may be effective on a given object. As such, it is not a review of the various manufacturer's products, but is a guide to which type of filter might be more useful. Individual preferences (greatest brightness/nebulosity vs. greatest contrast) will tend to guide the obsever as to which filter they would choose for viewing a given object, which accounts for some of the variation in results. However, there are a number of objects which certain filters should *not* be used on, and I indicate that in the comments section. The H-Beta tended to be in this "not recommended" category a lot.

As I indicated in the text, the judgement of which filter was best was based on a number of factors which were all weighted together, rather than just on one. These factors include nebula brightness, the total area of nebulosity shown, and the relative contrast of the features visible within the nebula. The OIII as a general trend tended to provide somewhat more contrast (especially on many planetary nebulae), but the UHC generally showed a greater total area of nebulosity at a somewhat higher brightness level than the OIII. On M27, the object showed the largest area of nebulosity at the highest level of brightness with the UHC filter when compared to the OIII. This was particularly noticable on the faint outer "wings" of the nebula, which are much less prominent in the OIII. Under some moderate to severe light pollution, the OIII may have to be used over the UHC just to screen-out some of the light pollution a bit more effectively, but under mild skyglow to dark-sky conditions, the UHC was the clear winner. The H-Beta filter showed the nebula, but the outer wings were gone, and the dumbell form was not as large or as bright as in the other filters. A similar situation occurs with M76, although the OIII does provide a higher level of contrast as I noted in the detailed results. For M57, there is a very faint irregular outer shell around the object and this was best seen from a dark sky site with the UHC filter. While the OIII will give more contrast, the outer shells were more difficult to see than they were in the UHC filter. At higher powers (and to some extent, with some smaller apertures) a narrowband filter like the UHC may show a bit of an advantage over the OIII, although the OIII is still very useful, even in some rather small apertures.

As for why the Lumicon line was the only one used, the original limited survey was done many years ago when I only had the Lumicon set and the other company's filters were just coming into existance (the only company that had an OIII or H-Beta was Lumicon). In science, for proper repeatability and consistency, it is best to use the very same equipment that you started with when making an observation during an extended project, so that differences in results are not due to the differing equipment. Again, this is a nebula "survey" and not really a review article. I have tested a number of narrow-band and line filters, and the Lumicons tended to be the "gold standard" on which to compare (i.e. the UHC had greater than 90% transmission from 480nm to 510nm). The Meade Narrowband tended to have a passband which was almost identical to that of the UHC, while the Orion Ultrablock has a more "Gaussian" passband, with slight fall-offs in brightness on the blue and red sides of the central maximum. This gave a very slightly darker image than the UHC, although in practice, the Ultrablock and UHC yield a nearly identical degree of image enhancement. The Astronomik UHC also gives results which are very similar to that of the Lumicon UHC. The DGM Optics NPB has a primary passband that is slightly narrower than the Lumicon UHC, but which still takes in the OIII and H-Beta lines (as well as H-alpha, which generally isn't that important except with very large apertures). I like it slightly more than the Lumicon UHC, but again, the difference isn't exactly like night and day. As for the OIII's, the Thousand Oaks model again is quite similar to the early OIII's by Lumicon, except that, to avoid the red "ghosting" in star images caused by Lumicon's "red leak" passband, the Thousand Oaks Type III did not have any red transmission (the newer 2" Lumicon OIII's also no longer have any red transmission). The Tele Vue Bandmate OIII has a little too broad a passband to be considered a "true" OIII, so it does not provide quite the same level of contrast enhancement that the Lumicon and Astronomik OIII's tend to provide. With the H-Beta, again, the Astronomik model is fairly similar to my Lumicon H-Beta in overall performance. In most cases, once you get to 90% transmission and include the proper emission lines with steep passband skirts, the various manufacturer products perform in a very similar manner, especially when considering which "type" of filter (i.e. broadband vs. narrowband, vs. line) is best to use on a given object. Clear skies to you.


I'll chose to disagree for the most part, sir.

#15 ric_capucho

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Posted 06 October 2006 - 07:26 AM

A fantastic resource for all of us! Thank you!

Ric

#16 Jim7728

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Posted 06 October 2006 - 10:11 AM

Thank you, David.

We appreciate the work and effort you put into that very informative article. :bow:

#17 Alvin Huey

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Posted 06 October 2006 - 01:17 PM

Thanks David for updating this already wonderful resource. I point people to your document on a regular basis; those who listen and have tight budgets, get the UHC/UltraBlock/whatever narrowband, then O-III second...works almost every time.

I also understand that there are some brand differences and thanks for clarifying with everyone else here that you are comparing by "types" of filters, not brand, etc. I tell them to get whatever narrowband filter they feel like, but just get one. :)

I use a 15+ year old UltraBlock, Lumicon O-III and H-Beta.

#18 David Knisely

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Posted 06 October 2006 - 01:22 PM

reflector74 posted:

I'll chose to disagree for the most part, sir.


You disagree on what specifically? Again, as I state in the article, in many cases, two filters may give two different benefits (usually brightness and area vs. increased contrast and dark detail), so the choice will depend at least in part on which benefit seems more important to the user. For example, many people like the North America Nebula better in the UHC filter. It is brighter and a tad larger, and the stars in the field tend to be a little more prominent than they are in the OIII. However, in the OIII, the nebula, while a bit fainter, is noticably sharper than it is in the UHC, so I kind of like that more of a "defining" effect. With any degree of light pollution, the OIII becomes a better filter to use on the North America, as it will tend to screen out the skyglow a little more effectively, but under dark skies, the choice becomes less clear. Clear skies to you.

#19 jmcdonald

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Posted 06 October 2006 - 02:03 PM

Thanks so much for taking the time to do this writeup David. It's not only a useful filter guide but a useful general nebula viewing guide.

#20 spaceydee

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Posted 06 October 2006 - 02:23 PM

David, I really enjoyed reading this article, even though to be honest I have not read every description of every observation of each object. I was happy to see that the h-beta filter is useful on more objects than just the horse-head nebula! I have avoided buying one mostly because I felt I'd never see that one anyway - but it looks like there is fun to be had with that filter on other objects, so I may add one to my equipment list sooner rather than later (although not sure of priority still).

thanks again.

#21 stevecoe

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Posted 06 October 2006 - 02:32 PM

David;

As always, a terrific write up with lots of great info. We agree instantly that the UHC is the filter to have. I have also been using my Deep Sky more often. On some low surface brightness objects it does provide a better view than the UHC. The Deep Sky seems to allow more of the faint nebulosity through to my eye and is a "gentler" filter.

After your article I may put the H-Beta on my Christmas list, it does seem that you are finding it useful for more and more objects. I had been stuck at the fact that it was only useful for the the California Nebula and Barnard's Loop. You have done a great job is showing that it is more useful than that.

Seeing as how we both piggyback a 100mm Orion refractor on an SCT, I have found that the larger nebulae are really fun with the RFT refractor. That wide field of view, I usually put the 27mm Panoptic or 21mm Stratus into the refractor, gives a great image of many large nebulae and shows smaller objects afloat in the Milky Way. A good filter really enhances that view. M 17, North American, Sword of Orion and IC 1805 in CAS are all excellent with the 4 incher. So, don't neglect a good filter if you have a small scope.

Thanks for your expertise;
Steve Coe

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#22 Alvin Huey

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Posted 06 October 2006 - 04:43 PM

Like Steve, I like to use my Genesis for the really big stuff. But I don't have it mounted on a SCT ('cause I don't have one. :) Just mount it on my SVP mount) I also was reluctant to get a H-beta filter 'till a few months ago...bought it from AM from a guy who bought it from someone else...apparently it is one of the originals as it came in a blue case. I saw incredible structure on the California nebula with the Genesis!

Also I wonder why reflector74 disagrees. I agree with David's article 100% and I've been obseving seriously for more than 30 years. Maybe it is presonal differences which David clearly states in his article...that it is subjective.

Oh, re-reading his original post, reflector74, are you refering to Abell PNe's? Perhaps they might fall under the "O-III" only rule. I remember that a few abell PNe's were visible only in an O-III.

CS,
Alvin #26

#23 David Knisely

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Posted 07 October 2006 - 12:20 AM

David, I really enjoyed reading this article, even though to be honest I have not read every description of every observation of each object. I was happy to see that the h-beta filter is useful on more objects than just the horse-head nebula! I have avoided buying one mostly because I felt I'd never see that one anyway - but it looks like there is fun to be had with that filter on other objects, so I may add one to my equipment list sooner rather than later (although not sure of priority still).

thanks again.


Yes, the H-Beta is useful on a number of objects. In fact, the view of the North America Nebula in the H-Beta is almost as good as it is in the OIII filter, but it is fainter, so most people will still either want to use the OIII or the UHC (or in my case, the DGM Optics NPB filter). The H-Beta also shows some interesting structural details inside M42 which are not seen as well in other filters. Here is a listing of the objects which I consider to be "H-Beta" objects:

USEFUL TARGETS FOR THE H-BETA FILTER

While the H-Beta is probably one of the less-used nebula filters, the idea that it works only on a handful of objects is not true. Here is a list of the more prominent objects that the H-Beta may be at least somewhat useful on. Some may require larger apertures, but a few have been seen from a dark sky site by just holding the filter up to the unaided eye and looking at the sky). Some of these will also be helped by a narrow-band filter like the Lumicon UHC.

1. IC 434 (HORSEHEAD NEBULA)
2. NGC 1499 (CALIFORNIA NEBULA, naked eye and Rich Field Telescope (RFT))
3. M43 (part of the Great Orion Nebula)
4. IC 5146 (COCOON NEBULA in Cygnus)
5. M20 (TRIFID NEBULA, main section)
6. NGC 2327 (diffuse nebula in Monoceros)
7. IC 417 (diffuse Nebula in Auriga)
8. IC 1318 GAMMA CYGNI NEBULA (diffuse nebula in Cygnus)
9. IC 2177: (Diffuse Nebula, Monoceros)
10. IC 5076 (diffuse nebula, Cygnus)
11. PK64+5.1 "CAMPBELL'S HYDROGEN STAR" Cygnus (PNG 64.7+5.0)
12. Sh2-235 (diffuse nebula in Auriga).
13. Sh2-276 "BARNARD'S LOOP" (diffuse nebula in Orion, naked eye or in RFT).
14. IC 2162 (diffuse nebula in northern Orion)
15 Sh2-254 (diffuse nebula in northern Orion near IC 2162)
16. Sh2-256-7 (diffuse nebula in northern Orion near IC 2162)
17. vdB93 (Gum-1) (diffuse nebula in Monoceros near IC 2177)
18. Lambda Orionis nebular complex (very large, naked-eye)


Clear skies to you.

#24 David Knisely

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Posted 07 October 2006 - 12:33 AM

Like Steve, I like to use my Genesis for the really big stuff. But I don't have it mounted on a SCT ('cause I don't have one. :) Just mount it on my SVP mount) I also was reluctant to get a H-beta filter 'till a few months ago...bought it from AM from a guy who bought it from someone else...apparently it is one of the originals as it came in a blue case. I saw incredible structure on the California nebula with the Genesis!

Also I wonder why reflector74 disagrees. I agree with David's article 100% and I've been obseving seriously for more than 30 years. Maybe it is presonal differences which David clearly states in his article...that it is subjective.

Oh, re-reading his original post, reflector74, are you refering to Abell PNe's? Perhaps they might fall under the "O-III" only rule. I remember that a few abell PNe's were visible only in an O-III.

CS,
Alvin #26


Well, of all the planetary nebulae I have observed with filters under fairly dark sky conditions, I have found *zero* that were not at least faintly visible with narrow-band filters like the UHC. Some might need the OIII to find in the first place, and may display much more contrast in the OIII, but they were still visible in narrow-band filters. In fact, when using the OIII to "blink" the tiny nearly stellar planetaries, I find that once I locate them, I can usually see them at least fairly easily even without a filter. For locating the big faint guys, I will often go first with a narrow-band filter and then try the OIII once I locate the object. Two real faint "monsters" that I did this with are the Medusa Nebula (PK205+14.1 in Gemini) and the "Headphone" Nebula (PK164+31.1 in Lynx). With any significant skyglow, the OIII may have to be reached for first however. Clear skies to you.

#25 stevecoe

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Posted 07 October 2006 - 02:18 AM

David;

Thanks very much for the H-Beta list, I will try some of those once I get my hands on the filter.

Clear Skies;
Steve Coe


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