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Hi MBADDAH & All,
I'd have to respectfully disagree with a few opinions offered above, while agreeing with some others. In making this post I assume you own a telescope of at least 8" aperture. I won't comment on brand though.
For mine, the coloured filters are a waste of time. I prefer the natural view of planets and I don't think there are big gains to be made in contrast with the use of coloured filters. They are of no help I can see on deep-sky stuff. I own a 23A light red that gets used for 2 mins, once every 5th pancake day on Mars. I also think a SWAN-band filter can occasionally be useful on comets -- particularly on the ion tails.
Deep Sky observing is very different.
There are three basic types of visual-use filters --
(1) "Deep-sky" type filters that are supposed to make a general improvement on all types of objects by blocking light-pollution type wavelengths.
(2) "Narrow-band" filters (like the UHC filter) that are designed to pass both the doubly ionised oxygen lines (ie O III) _AND ALSO_ the nearby H-Beta Line.
(3) "Line-filters" that are designed to _either_ pass the O III _OR_ H-Beta.
The Deep-sky filters are of very limited assistance. They really only work on nebulae and despite the claims, I think, actually make any other types of objects (eg galaxies, clusters) dimmer.
The Narrow-band or UHC type filter is an extremely useful one. It will make a considerable improvement on virtually any emission or planetary nebula, whether you are in the suburbs or under a dark sky. It is like bolting on an extra 2" of aperture _for those types of objects_. There are very few nebulae that won't look better with a UHC in 8" and above 'scopes. The exceptions are those few nebulae that shine at odd-wavelengths for some reason and/or don't have strong O III or H-Beta emission.
Line filters can be pretty useful too. The O III is best for planetary nebulae that frequently shine strongly in the dual O III wavelengths. The H-Beta filter is very specialised and only works well on a few select objects. The California Nebula (NGC 1499) and the Horsehead Nebulae complex (IC 434) are two prominent examples. Because these filters have such a narrow band-pass, I wouldn't use either of these line filters on 'scopes less than 25cm. I probably wouldn't use the H-Beta on less than 40cm actually.
In summary,
Deep-sky filter -- waste of time IMHO.
UHC -- Excellent choice for 8" and above 'scopes for a big general improvement on planetary and emission nebulae. Even works well on Horsehead and comets (ion tail).
O III -- For 25cm and above on Planetary Nebulae in particular will provide a further small contrast enhancement over the UHC.
H-Beta -- For 40cm an above on very faint nebulae that have significant H-Beta emission. In a 46cm 'scope, the improvement on the horsehead has to be seen to be believed.
Over time I've acquired
1.25" -- UHC and O III
2" -- UHC and H-Beta.
Best wishes with your choice!
Best,
Les D
Contributing Editor
AS&T
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