Telescope filters are a common accessory in amateur astronomy and can substantially improve your views of the moon, galaxies, and pretty much everything unless you live on a deserted island thousands of miles away from the nearest light bulb. So what telescope filters should i buy? That depends on what you want to do.
Astronomy filters explained
The general reason for these filters (other than the moon filter) is to increase contrast between things in your eyepiece making them easier to see.
A light pollution filter is probably the most generic of these types of filters and are designed to block out certain wavelengths of light such as light being created by sodium vapor, mercury, fluorescent, and other man made sources of light that are typically found in outdoor lighting. By blocking those types of light, but allowing others, the night sky tends to appear blacker while objects such as nebulae and galaxies tend to stand out more in the eyepiece.
Colored filters have the same type of effect such as enhancing surface detail, dust clouds, and polar ice caps on Mars. Many people use different colored filters when they are viewing the planets because a red filter will increase the visibility of features that a blue filter might not, and the opposite is also true. Colored filters can also do things like help split stars and increase visibility of galaxies (light to medium blue in particular for these cases).
This Celestron 1.25″ Mars Observing Eyepiece Filter combines the effects of a red and a blue filter which are probably the best filters to use on Mars, into one convenient package. While I am not sure it provides all the detail you can see with two separate filters, it certainly comes very close which makes this a huge time saver.
I can not tell you how much time some observers waste swapping out filters looking for that last little bit of detail in one part of the planet or another. The ability to see increased detail in multiple parts at the same time makes this filter an obvious choice for anyone who really wants to see the red planet.
This is truly a high quality filter with a metal cell, glass optics, and excellent multi-coatings to provide the absolute highest quality image possible, which is very important when trying to coax detail out of another planet.
A UHC (Ultra High Contrast) or nebula filter like the Solomark 1.25 Inch UHC Light Pollution Reduction Filter is much more than just a light pollution filter. How do nebula filters work? They target and only allow wavelengths of light specific to celestial objects ensuring the maximum contrast, and therefor the maximum visibility of deep space objects.
These are particularly useful with nebulae, either reflection or emission. I have had great results on a wide variety of nebulae, although results with planets and galaxies have been much less improved.
I would recommend a UHC filter like this one only for nebulae, but with that it does make a nice difference and keeps you from having to use multiple filters with each nebula to see which one works best. Simply use this one on all nebulae, then switch to something else for planets and galaxies.
If you want a UHC filter, and want something really outstanding, try the Orion 5654 1.25-Inch UltraBlock NarrowBand Filter from Orion Telescopes. This is probably one of the best telescope filters for nebula, and it does a reasonable job on other targets such as galaxies and planets too although that is not its primary focus.
This is the visual version of their Skyglow astrophotography filter and both are excellent choices for their application. Blocking out not just light pollution, this filter goes further and filters out light that is not directly associated with nebulae. This substantially increases contrast making empty space really dark black so that the light of the nebula can be more easily seen in the eyepiece.
If you want to see nebulae and live where there is light pollution (and who doesn’t these days), you need a UHC filter and this one is an excellent choice and is considered a best uhc filter.
Basic telescope filters in sets
This Neewer 1.25 inches Telescope Filter Set is a great place to start when you want a set. The quality of these filters is not bad, particularly with the extremely low price point. I am not overly impressed with either the circular polarizer or the moon & skyglow filter they do give you an excellent taste of what you can do with those filters.
What I really like is that at this price someone can afford to buy the set just to see if a set of telescope filters will help with what they want to do. Then, if it doesn’t help, no big deal. If they do help, you can then decide if a higher quality set might be something you are interested in. If you have any doubts about buying filters at all, I highly recommend trying this set first.
The entire set comes in a nice little soft case making it easy to carry out to the dark site. Nice touch.
The Orion 5590 Deluxe Stargazer’s 1.25-Inch Eyepiece Filter Set is a much nicer set and is a more practical once you have determined that you really want a set like this. Just like the previous set it includes the standard four color filters and a moon & skyglow filter. Where this one differs, other than better quality, is that it includes a variable polarizing filter. Considering that a variable polarizing filter is about $35 by itself, this makes this kit a really good deal.
I found that these color telescope filters work better at increasing contrast and blocking unwanted light than the cheaper sets. The moon & skyglow filter is far and away better than the one in the previous kit and is one of my absolute favorite light pollution filters. With the inclusion of the variable polarizing filter in place of a standard moon filter, images of the moon are not only adjustable for brightness, but also look far sharper due to the polarizing effect.
Overall this is an excellent set of telescope filters and should be the choice if you are even remotely serious about astronomy. It will more than pay for itself with far better views.