What are good filters to buy for an 8" reflector?
I read somewhere that a telescope is better with the use of filters and a good eye piece. What would you recommended for a novice wanting to see galaxies and nebula?
If the scope is good, then yes, a good eyepiece will help you get the most out of the scope. If the scope is bad, a really expensive eyepiece (unless you’re planning on upgrading the scope) is a lot like polishing dog poo. It doesn’t make it any better than what it is.
For galaxies, I really think unfiltered is best. Galaxies emit light from the entire spectrum, so anything you do to filter the light from the galaxy is going to dim it more than it’s going to help.
For nebulae (especially emission nebulae) a "light pollution" or a "narrow band" filter like an OIII filter are going to be the most useful. Because these objects only emit light at particular frequencies, a filter can block all but those frequencies, darkening the sky and making the object more visible. The other suggestions you have gotten (blocking out extra light, averted vision, and jiggling the scope) also work very well–I use them all the time
here are some to check out
http://www.telescope.com/control/accessories/telescope-and-eyepiece-filters
http://www.telescopes.com/search/index.cfm?Ntt=nebula%20filter&Ntk=all&source=googleaw&kwid=nebula%20filter&tid=exact
References :
An Ultra High Contrast (UHC), OIII or nebula filter is a great workhorse filter for nebulae. These all operate in the "green" region of the visible light spectrum, which is where the human eye is most sensitive.
http://pages.sbcglobal.net/raycash/filters.htm
For galaxies there is nothing like dark skies for best results. However there are some "tricks of the trade" to help you.
1) Block out all light from around your head (a towel over your head works great). Use dim red lights. Let you eyes adjust to the dark for about 30 minutes before doing any serious observing.
2) Learn to use and develop your averted vision. Almost a Zen thing – look by not looking directly at an object. Parts of the rods in your eyes (the rods are used for night vision, cones for daytime) are located away from the center of the eye, where the fovea is (the point were all the optical nerve bundles come together to head back to your visual context). Spooky when it works, but an useful tool for visual observing.
http://www.orion-xt10.com/dark-adapted-averted-vision.html
3) Jiggle the scope. This is counterintuitive, but what this does is trigger the brain to look for motion, which in turn and makes you see something that might normally be hidden from view. Don’t need to jiggle it much, just a tap or two will suffice.
4) Drink in the view. Just look for long periods of time and just light your eye integrate the view. Also, keep both eyes open (I wear an eye patch). A good way to practice is on the Andromeda Galaxy. Star with the core and work outward along the arms. It’s amazing what detail you can pick up.
References :
While filters can enhance the view of some objects, I disagree with that first sentence. That may sound pedantic, but you should see your telescope as the instrument it is, and get used to unfiltered views first. Filters by definition also block part of what’s there.
For an 8" reflector, the priority would be a broadband filter which will reduce sky glow, and/or a narrowband nebular filter. These will bring out the brighter nebulae like Orion, the Triffid, and North American. An OIII (double-ionized oxygen) filter is good for these, and fainter ones as well, such as the Rosette. Galaxies generally aren’t enhanced by filters.
References :
If the scope is good, then yes, a good eyepiece will help you get the most out of the scope. If the scope is bad, a really expensive eyepiece (unless you’re planning on upgrading the scope) is a lot like polishing dog poo. It doesn’t make it any better than what it is.
For galaxies, I really think unfiltered is best. Galaxies emit light from the entire spectrum, so anything you do to filter the light from the galaxy is going to dim it more than it’s going to help.
For nebulae (especially emission nebulae) a "light pollution" or a "narrow band" filter like an OIII filter are going to be the most useful. Because these objects only emit light at particular frequencies, a filter can block all but those frequencies, darkening the sky and making the object more visible. The other suggestions you have gotten (blocking out extra light, averted vision, and jiggling the scope) also work very well–I use them all the time
References :
As always, the two best sources for information on telescopes and accessories are:
Terence Dickinson and Alan Dyer: The Backyard Astronomer’s Guide (Firefly)
Philip Harrington: Star Ware (Wiley)
I hardly ever use filters myself. The only one I use at all regularly is an OIII filter for enhancing planetary and diffuse nebulae. I sometimes use coloured filters to bring out certain features on Mars, but most of the time I prefer the unfiltered view.
Eyepieces are a much better investment that filters. My personal favourites are Tele Vue Naglers because of their sharpness, contrast, and wide fields of view. You very much get what you pay for with eyepieces. Since I use the same eyepieces on many different telescopes, I find them a good investment. I particularly like low and medium powers for deep sky objects, and high power, long eye relief eyepieces for lunar and planetary viewing. I use a binoviewer for much of my lunar and planetary observing because I find that I see more when I use both eyes.
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