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Date: 14 May 2005 23:48:28
From: Steven
Subject: Filter question
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Hi everybody,
I'm looking to purchase a filter to enhance my deep sky viewing
experience. I have a small 6" newtonian, good eyepieces (Vixen and
Celestron) and a lousy suburban observing spot. I did a little bit of
research, and I think that the best to buy in this situation would be
a broad band filter like the Orion Skyglow filter or the Lumicon Deep
Sky filter. But it never hurts to ask for other opinions :-) Any other
thoughts?
Regards,
Steven
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Date: 14 May 2005 22:43:26
From: Brian Tung
Subject: Re: Filter question
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Steven wrote:
> I'm looking to purchase a filter to enhance my deep sky viewing
> experience. I have a small 6" newtonian, good eyepieces (Vixen and
> Celestron) and a lousy suburban observing spot. I did a little bit of
> research, and I think that the best to buy in this situation would be
> a broad band filter like the Orion Skyglow filter or the Lumicon Deep
> Sky filter. But it never hurts to ask for other opinions :-) Any other
> thoughts?
I would recommend against a broadband filter as your first one. They
do help a little, but the effect is pretty slight. A narrowband filter
is a better choice, in my opinion. I have the Orion narrowband filter
and it's pretty good. It will permit you to see some objects that
aren't visible otherwise, but probably the more useful effect is that
it makes it easier to see the brighter objects that are otherwise a
bit lost in the sky glow.
For comparison, I usually use these filters with my 5-inch SCT, and
they are not at all useless with this size of telescope, despite what
others might say.
Incidentally, their benefit isn't limited to suburban use. There is
always some natural glow in the sky and the narrowband filters are as
useful, if not more so, under dark skies.
A line filter, like Lumicon's O-III filter, is another popular choice,
although with a 6-inch Newtonian, I'd probably give a slight nod to
the narrowband filters. But they're both pretty good. I'd also defer
the H-beta filter until considerably later.
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
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Date: 14 May 2005 15:25:41
From: Mean Mr Mustard
Subject: Re: Filter question
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Won't make a lick of difference on a 6". If you want to do DSOs
then you'll need to step up in aperture.
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Date: 15 May 2005 17:56:45
From: Ed T
Subject: Re: Filter question
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"Mean Mr Mustard" <macusr023@yahoo.com > wrote in message
news:1116109541.709789.275420@g44g2000cwa.googlegroups.com...
> Won't make a lick of difference on a 6". If you want to do DSOs
> then you'll need to step up in aperture.
>
Bullshit.
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Date: 15 May 2005 04:29:48
From:
Subject: Re: Filter question
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Steven wrote:
> Hi everybody,
>
> I'm looking to purchase a filter to enhance my deep sky viewing
> experience. I have a small 6" newtonian, good eyepieces (Vixen and
> Celestron) and a lousy suburban observing spot.
David Knisely's customary post says all there is to say about filters;
I don't have anything to add or subtract from it. But in case you want
something simpler ...
You *can* improve your views with a filter, but only for a few selected
objects -- the ones that emit light in very narrow color bands. But
there's really nothing you can do to get better views of galaxies and
star clusters except buy a bigger scope or find a better observing
site. Finding a darker site is particularly crucial for observing
galaxies; you'll get a better view of most galaxies in your 6" scope
from a dark site than you could in *any* telescope, no matter how
big, from a typical suburban site.
The good news is that the objects that are improved dramatically
by nebula filters include some of the most spectacular things in
the sky -- the Lagoon, the Veil, and many others. As for which
filter to get, I've always recommended a narrowband like the
Lumicon UHC or the Orion Ultrablock as the number one choice.
But I've got to admit that since buying an O-III filter, I've
used it a lot more than my UHC. And that's not just for big scopes;
it's also true even when using my puny 3.1-inch refractor.
- Tony Flanders
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Date: 15 May 2005 11:42:45
From: Dennis Woos
Subject: Re: Filter question
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> But I've got to admit that since buying an O-III filter, I've
> used it a lot more than my UHC. And that's not just for big scopes;
> it's also true even when using my puny 3.1-inch refractor.
In my 10" I use the OIII more than the UHC, but not so in smaller apertures.
However, I believe that, from previous posts on this topic, that David
Knisely agrees with you and also finds the OIII good with smaller apertures.
I think that this may boil down to a matter of personal taste - I don't
like how much the OIII kills stars on anything less than 10". Seems to me I
recently read a review of some OIII that didn't block stars as much as the
Lumicon - TV Nebustar?
I bet that you can try out many/all of these filters at a star party in your
area, and recommend that you do so before shelling out $. Who knows, you
may not like any of them very much.
Dennis
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Date: 15 May 2005 01:18:48
From: David Knisely
Subject: Re: Filter question
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Steven posted:
> I'm looking to purchase a filter to enhance my deep sky viewing experience. I have a small 6" newtonian, good eyepieces (Vixen and Celestron) and a lousy suburban observing spot. I did a little bit of research, and I think that the best to buy in this situation would be a broad band filter like the Orion Skyglow filter or the Lumicon Deep Sky filter. But it never hurts to ask for other opinions :-) Any other thoughts?
USEFUL FILTERS FOR VIEWING DEEP-SKY OBJECTS
by David Knisely
Prairie Astronomy Club
There are a number of different filters available on the market
today for improving the views of various Deep-Sky objects, with most
coming in one of three classes: 1. Broad-Band "light pollution"
filters, 2. Narrow-Band "Nebula" filters, and 3: Line filters.
BROAD-BAND "LIGHT-POLLUTION" FILTERS
The broad-band "Light-pollution Reduction (LPR) filters are
designed to improve the visibility of a variety of Deep-Sky objects by
blocking out the common Mercury vapor, Sodium, and some other emission
lines from man-made or natural sources which contribute to light
pollution, while letting through a broad range of other more useful
wavelengths. Since the eye is mainly a "contrast detector", this
selective screening out of some of the background skyglow increases the
contrast and helps Deep-sky objects stand out more noticably. While
these broad-band filters do not eliminate the effects of light pollution
or make the objects brighter, in many cases, these filters can improve
the visibility of some deep-sky objects to at least some degree. The
greatest improvement in the overall view is often found with emission
nebulae, but broadband filters can also give a slight contrast boost to
some reflection nebulae and a few of the larger more diffuse galaxies.
In addition, larger versions of these broadband filters which fit over
camera lenses can be somewhat useful for photography of wide star fields
when some skyglow is present.
Some available broad-band filters are the Lumicon Deep-Sky, the Meade
Series 4000 Broadband, the Celestron LPR, the Thousand Oaks Type 1, and
the Orion SkyGlow. The broadband filters can offer a noticable boost in
contrast and visibility of the fainter outer detail in emisson nebulae
over non-filtered views for objects like the Orion Nebula (M42), the
Lagoon Nebula (M8), the Merope Nebula, the Trifid (M20), and a number of
others. However, the improvement is not as noticable on star clusters
or galaxies. I have found that using the filter on larger and more
diffuse galaxies like M33, M81, M101, NGC 253 and NGC 2403 in my 10 inch
when weak skyglow is present will help boost the visibility of the
detail, but the effect is fairly mild. On star clusters, there is even
less of an effect, since some of their emission falls in the portions of
the spectrum blocked by these filters. In that case it may be better to
use slightly higher power on some of the smaller objects to dilute the
light pollution effect a bit. Since some light is blocked by the
filters, there can be times when a few objects may even look fainter
from a dark sky site when using a broad-band filter than without one.
Severe levels of light pollution may also be too much for the broad-band
filters to handle effectively, so you still want to find as dark an
observing site as you can and use averted vision. The broadband filter
has an additional bonus, as it does work fairly well as a blue filter
for observing Jupiter and for bringing out the white clouds and polar
caps of Mars. In summary, the broad band "light pollution" filter can
be useful in compensating for some light pollution, but may not be the
most impressive filter intended for deep-sky use.
NARROW-BAND "NEBULA" FILTERS
Narrow-band "Nebula" filters, as the name implies, are mainly
designed for viewing many emission nebulae. These filters allow only
the bright pair of emission lines of Oxygen III, the Hydrogen Beta
emission line, and wavelengths between H-beta and the OIII lines to get
through. Narrow-band filters darken the background skyglow
significantly without hurting the nebula, and are often of considerable
help when observing in mild to moderate light pollution. The filter's
improvement of the view of emission nebulae is usually superior to that
of the broadband filters, as many faint nebular objects become much
easier to see (without the filter, some may not be visible at all!).
Even the more prominent nebulae which are visible without filters gain
considerable detail and contrast with the narrow band units. However,
you still need to use proper dark adaptation, averted vision and low
to moderate powers (3.7x to 10x per inch of aperture) to get the most
out of these filters. Many of those who have tried narrow-band filters
and had problems usually are not getting dark adapted enough or are
using the wrong power range. To get dark adapted enough for those
observing under urban settings, shielding from any local light sources
is a must.
Some available narrow-band filters are the Lumicon UHC, Astronomik
UHC, Meade Series 4000 Narrowband, Thousand Oaks Type 2, and Orion
Ultrablock. The UHC and Meade Narrowband also have a deep-red passband
for the Hydrogen Alpha line. Both the UHC and Ultrablock will, for
example, often show the Rosette Nebula TO THE UNAIDED EYE when you look
through them from a dark sky site. Even under a really dark sky, the
contrast and detail improvements are impressive, and most observers
continue to use their narrow-band filters at such dark-sky sites. One
neat trick for finding tiny planetary nebulae is to "blink" the objects
by holding a narrow-band filter between the eyepiece and the eye. The
stars in the field will dim somewhat, but the planetary nebula will
remain undimmed, thus standing out from the background stars.
In comparison, the UHC and Ultrablock have very similar
characteristics, although the UHC has a slightly higher light
transmission factor in its primary passband than the Ultrablock, which
may be helpful for viewing faint nebulae. The Meade Narrowband filter
has a passband quite similar to that of the UHC. Spectroscopic
comparison of the two filters reveals that the Ultrablock's passband is
more rounded and slightly narrower than the more flat-topped UHC, with
falloffs in light transmission towards the passband edges, especially
towards the H-beta side. The UHC also shows a red "leak" passband
including the H-alpha line (the Ultrablock doesn't have one), which may
contribute to the image brightness with larger apertures. The
Ultrablock's more rounded and slightly narrower passband may be reasons
why some observers have reported a bit darker field and slightly higher
contrast under light pollution with some objects using the Ultrablock.
At times the Ultrablock has also been slightly less expensive than the
UHC, but when not sale priced, the two filters are of similar cost.
Both will perform very well, and the overall difference between them is
very slight. However, these "nebula" filters usually slightly reduce
the brightness of most star clusters, reflection nebulae, and galaxies,
although in moderate light pollution, a narrowband filter may still be
of some use on these objects with larger apertures. Photographic use of
these narrow band filters is also not recommended.
LINE FILTERS
Line Filters are very narrow passband specialty units which are
designed to let in only one or two spectral lines from emission nebulae,
such as the close pair of Oxygen III lines or the Hydrogen-Beta line.
In the line filter category, the Oxygen III (OIII) filter is the real
standout. Its very narrow bandwidth allows only the pair of emission
lines of Oxygen to get to the eye, and for many planetary and some
diffuse emission nebulae, the boost in contrast has to be seen to be
believed! The Veil and Helix Nebulae look like photographs in a 10"
with the OIII filter, and some of the "green box" emission nebulae in
SKY ATLAS 2000.0 jump out at you. You may even see some nebulae which
are not shown on some atlases. This filter is often the best one for
many planetary nebulae, with the "blinking" technique becoming vastly
more effective, as the stars nearly vanish, leaving the planetary
standing out like a sore thumb. However, since the bandwidth of the
OIII filter is so narrow, it may hurt some nebulae with significant
H-beta emission somewhat, like the nebulae around Gamma Cygni or the
Horsehead. Differences between this filter and narrow-band filters like
the Lumicon UHC are mainly in nebula visibility and contrast. Many
nebulae show a slightly larger area of nebulosity in the UHC filter with
slightly higher brightness, but in the OIII filter, they will often have
more contrast and dark detail. However, the OIII filter really dims the
view of star clusters and galaxies even more than the narrow band
filters do, although observers with large telescopes may find the OIII
useful for bringing out a few emission nebulae in other galaxies, like
the HII regions in M33. A few of the older Lumicon and Meade models
also have a substantial red passband, and on bright emission nebulae
like M42 and M8, weak red color in parts of the nebulae have been
reported visually usingmoderate to large apertures. Recently, Thousand
Oaks has produced its "Type-3" Oxygen III filter, as has Astronomik. It
doesn't seems to have the tiny "red-ghosting" secondary star images that
the Lumicon model does, yielding more point-like star images, although
its overall performance in enhancing nebulae is quite similar to the
Lumicon model. Meade has also introduced its own OIII filter.
Another somewhat less-used line filter is the H-Beta. As the name
indicates, the filter only lets through the H-Beta emission line of
hydrogen, and is best known for its effect on the Horsehead Nebula, the
California Nebula, the Coccoon Nebula, and a few others. On an 8" to
10" scope, the Horsehead Nebula goes from near invisibility to
visibility, and the California Nebula becomes fairly easy, gaining a
great deal of contrast and filamentary detail. An improvement over
non-filter use for additional objects like M42/43, the North America
Nebula, and a few others can also be noted, but in many cases, these
other objects can appear somewhat better overall in the UHC or OIII
filters. The H-beta can also be used to observe some of the structural
details of some brighter nebulae by comparing the H-beta view with that
in other filters. However, the H-beta does not usually work well on
most planetary nebulae, as it nearly wipes out some of them and greatly
dims most of the rest. The total number of emission nebulae which the
H-beta will significantly improve is somewhat limited. Many of these
"H-beta" objects tend to be fairly faint to begin with (like the
Horsehead) and require larger apertures for decent views even with the
filter. Unless you REALLY like looking at these faint H-beta targets,
you may be able to do without the H-Beta filter, at least for a while.
Thousand Oaks also makes their "Type-4" version of the H-beta filter, as
does Astronomik.
For recommendations, if you can afford only one filter, get a
narrowband filter like the Lumicon UHC, Meade 4000 Series Narrowband, or
Orion Ultrablock (whichever is least expensive at the time). If you can
afford to get two filters, the OIII makes a good companion filter to a
narrowband one but remember to use them with an eye that is properly
dark adapted and employ averted vision. Filters won't make the objects
brighter, but in many cases, they can make many of them a lot easier to
see. Have fun and clear skies to you.!
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
**********************************************
* Attend the 12th Annual NEBRASKA STAR PARTY *
* y 31 - Aug. 5, 2005, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
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Date: 15 May 2005 20:32:13
From: Steven
Subject: Re: Filter question
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Thanks to you all for the helpful advice, it is very much appreciated.
But it confuses me: if broadband filters such as these do not work,
why are they still being made by high-profile companies such as
Lumicon? What application do they have?
I'm not expecting the light pollution to magically disappear. I know
that the filter will dim everything but my eyes are not that sensitive
to contrast, so I was hoping that these filters at least help to solve
that. This way I would get a clearer view of some fuzzies - I'm
talking about galaxies like M65 and M66, not the really faint ones. Of
course, going for a bigger scope and a darker location would be much
better, but that's not happening soon. And it would probably cost me
more than a simple filter.
I'm shying away from the narrowband and line filters because I feel
these will dim objects too much for my modest aperture. That was a
decision based mostly on David Knisely's excellent text (thanks!)
which made broadband filters sound more like an 'all-round' filter.
Does that sound like the right conclusion, or am I still going to
profit more from buying a UHC?
Again, thanks for any further input on this...
Regards,
Steven
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Date: 15 May 2005 18:47:17
From: Brian Tung
Subject: Re: Filter question
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Steven wrote:
> Thanks to you all for the helpful advice, it is very much appreciated.
> But it confuses me: if broadband filters such as these do not work,
> why are they still being made by high-profile companies such as
> Lumicon? What application do they have?
It's not that they don't work. It's just that the effect is subtle
enough that I wouldn't buy it as a *first* filter. A second or third
filter, perhaps. But not first. It's just a cost-benefit consideration.
The advantage of the broadband filter over the narrowband filter is that
it works on more objects. The effect is slight, but what it does it does
with galaxies and globular clusters in addition to emission nebulae. I
used it to help me see M1, the Crab Nebula, from a light-polluted area,
but it was still a very difficult see.
> I'm shying away from the narrowband and line filters because I feel
> these will dim objects too much for my modest aperture. That was a
> decision based mostly on David Knisely's excellent text (thanks!)
> which made broadband filters sound more like an 'all-round' filter.
> Does that sound like the right conclusion, or am I still going to
> profit more from buying a UHC?
As I said, they are more of an all-around filter. But you'll see more
benefit from a narrowband filter. I use my narrowband filter with my
5-inch scope far more often than my broadband filter.
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
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Date:
From: Martin Brown
Subject: Re: Filter question
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Date: 16 May 2005 10:39:59
From: Steven
Subject: Re: Filter question
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OK, thanks Martin and Brian for answering my further questions. I
think I'll go for the narrowband filter then (a Baader UHC, because
they're the only ones in my price range) and save the broadband filter
for later, for photographic use.
You've all been very helpful :-)
Regards,
Steven
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Date: 16 May 2005 16:42:02
From: GPA
Subject: Re: Filter question
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I found the following link to be very helpful in terms of the question of
"what filters help with what objects":
http://www.cloudynights.com/howto/filters.htm
Meanwhile, does anyone have an opinion or experience with the Celestron
UHC/LPR filter? How does it compare with the Lumicon UHC (other than being
almost half the price)? Is it a "broadband" or "narrowband" filter?
Thanks!
Gerry
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Date: 17 May 2005 21:45:24
From: William Hamblen
Subject: Re: Filter question
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On 2005-05-16, GPA <bravewords2NOSPAM@yahoo.ca > wrote:
> Meanwhile, does anyone have an opinion or experience with the Celestron
> UHC/LPR filter? How does it compare with the Lumicon UHC (other than being
> almost half the price)? Is it a "broadband" or "narrowband" filter?
My old Celestron LPR filter is closer to a Lumicon UHC than the
Lumicon Deep Sky. By old I mean about 1990. What I don't like about
LPR filters is the green color, which comes with the territory but is
still unattractive.
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Date: 18 May 2005 07:16:14
From: shneor
Subject: Re: Filter question
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Hi David,
One excellent filter you left out is the DGM Optics NPB. It's like a
UHC, with less starlight color distortion and a significantly brighter
image. I sold my (premium) UHC which I had owned for several years when
I purchased the DGM, as the results are noticeably better than the UHC.
Another advantage of the DGM is it's low price - about $105 for a 2".
Clear skies,
Shneor
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Date: 22 May 2005 14:44:50
From: Steven
Subject: Re: Filter question
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Hello everybody,
Just so you know: I was planning to wait a few more months and test a
few filters, especially the Lumicon UHC.
However, at the Astromesse in Germany I found a Lumicon Deepsky Filter
that looked very interesting. It also had a very interesting (second
hand) price tag, so I thought 'why wait' and I bought it. All good
advice and intentions are put aside when there's a bargain in sight ;-)
When the obligatory two weeks of bad weather have passed, I'll post
some of my thoughts.
Regards,
Steven
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