Allow me to quote this post from yahoo group "Skyquest Telescopes" which pretty much sums up the benifets of various filter types.
---------------------------------------------------------
This question is asked countless times so I have summarised about 10
of my recent posts on this topic below, it is fairly lengthy but
explains a bit about filters to you.
Several companies produce what is known as a "broadband"
filter or known otherwise as a "light pollution reduction"
filter(LPR). These are sold as the Orion Skyglow, Thousand Oaks LP1
Broadband, Lumicon Deep Sky, Celestron LPR, Meade Broadband Nebula
Filter, there are also a couple of others. These filters despite
the claims of the various manufacturers, provide minimal benefit for
visual observation from any sky conditions, neither dark site or
light polluted. The Broadband or LPR filters provide some benefit for
astrophotography purposes.
Broadband or LPR filters are not recommended for visual observation
regardless of prevailing sky conditions IMHO.
Several companies also produce "Narrowband" filters. For a person
that is only going to own 1 filter, a narrowband or UHC is the
best type to get, an O-III would be the 2nd filter to aquire and the
3rd probably a H-Beta as they work on a progressively lower number of
objects. If the telescope you own is over 16" aperture I might
suggest you aquire an OIII filter as the 1st filter and a UHC filter
as the 2nd filter.
The UHC filters work on a large number of different targets and in
semi-light polluted skies to dark skies. They do not make anything
brighter, they reduce unwanted wavelengths of light thereby making
more detail visible in the target object. Generally the UHC filters
work best on emission and planetary nebula, however they can offer a
slight improvement to other targets as well. You should also note
that there are no filters available that will dramatically improve
the view of galaxies and globular clusters, the only way to improve
the view of those targets is to travel to a dark sky site.
The better narrowband filters are sold as UHC Filters by Lumicon and
Astronomiks, Thousand Oaks LP-2 Narrowband, Orion Ultrablock and
Meade Narrowband, Televue have just released a Narrowband filter sold
as the Televue Bandmate Nebustar filter. I have had no feedback on
the Televue product but if it is like most other Televue products it
will sit at the top end of the tree. All of these filters have
slightly different bandpass characteristics. eg. The Astronomiks and
Lumicon have a wide H-Alpha Bandpass, the Meade Narrowband has a
clipped H-Alpha bandpass and the Orion Ultrablock and the Thousand
Oaks LP2 have a minimal light pass in H-Alpha.
I have also used the Sirius Optics (SO) filters and optically these
are very good however I do not recommend them as they are surface
coated on the eye-lens side of the filter and they are very easily
scratched and damaged. SO recommends you leave them permanently
attached to an eyepiece to avoid damage. I don't like owning things
that are easily broken yet I still own often use 2 of them
.
I have used most of the UHC/Narrowband filters and in my opinion the
Astronomiks is superior to all the others with the Lumicon UHC and
the Orion Ultrablock tied for 2nd place and exceptionally good
filters BTW. For USA users the Orion Ultrablock realistically
represents the best value for money as it is considerably cheaper
than the others and it is a subjective call as to whether or not it
is just as good as the others. Many experienced observers that have
used all the narrowband filters except the Astronomiks rate the Orion
Ultrablock at the top of the list. Importantly the Ultrablock is only
1/2 the price, albeit now made in China or Korea or somewhere like
that. The Lumicon I believe is made in the USA and the Astronomiks is
made in Germany. I have yet to find anyone that has used the
Astronomiks UHC that does not rate it as the best UHC available.
The Astronomiks is extremely well constructed mechanically, the glass
used is extremely hard and highly polished making the external
surfaces very durable, it has an unconditional 5 year replacement
guarantee, they would not give that if they thought you could scratch
it easily. The other filters have a finite lifespan, the Lumicon
after a number of years absorbs moisture between the glass layers and
the filter material can become a little spotty, they are generally
accepted to last about 8 to 10 years. I believe that the Astronomiks
may last longer than this but of course this is yet to be tested as
it has only become available in Australia and USA fairly recently.
Optically the differences are not mind blowing but they are apparent.
I have never had them all side by side in the same scope so a lot of
my evaluation is from memory. To me the Astronomiks allows a little
more detail to be picked up than the others and importantly it does
not darken the surrounding background objects quite as much as the
others. It is very good on Emission Nebula incorporating clusters,
like M8, M20, M42 and NGC2239 because it increases the contrast of
the nebula significantly, while leaving the stars of the incorporated
clusters clearly visible. I have now owned the Astronomiks for about
6 months and I have given the filter a good try on the following
objects:-
NGC246 Planetary neb in Cetus
NGC1360 Planetary neb in Fornax
NGC253 Large Edge on Galaxy in Sculptor <didn't do much and
nor should it, but hey it was worth a try
>
NGC2070 Tarantula Nebula in Dorado
NGC7293 Helix Nebula in Aquarius
NGC7009 Saturn Nebula in Aquarius
M8,M17,M20 Emission Nebula in Sagittarius
M16 Emission Nebula in Serpens
M42, M43 Orion Nebula in Orion
NGC 3242 Ghost of Jupiter Planetary in Hydra
NGC 3918 Blue Planetary in Centaurus
NGC3132 Eight Burst Nebula in Vela
NGC2239 Rosette Nebula in Monoceros
It performed exceptionally well on these targets IMHO and slightly
better than the other Narrowband filters I have previously used,
possibly by as much as 15% or so.
The Astronomiks UHC is available from:-
http://tinyurl.com/u03c
The Orion Ultrablock and the Lumicon UHC are readily available from
the following manufacturers.
http://tinyurl.com/2z3e3
http://www.lumicon.com/uf.htm
Clear Skies
John Bambury
