Telescope filters change your night sky observation game. They do exactly what their name implies, filtering out or reducing specific light wavelengths while allowing others to pass through.
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When these wavelengths no longer reach your eyes, your visibility improves. So you’ll see some colors more vividly, which makes your viewing target pop. Filters also cut glare so that you can take crisper images with more details.
You might be wondering which filters you need, so we’ll try to simplify your selection process.
Think of colored filters like stained glass. For example, green glass absorbs the sunlight’s wavelengths and only lets green color shine through. Telescope filters work in the same way.
Astronomical Objects: Light and Color
The light and colors from celestial objects come from differing electromagnetic waves. Some of it is visible light you can see through your telescope, like the white of stars. And some astronomical objects’ light isn’t visible to human eyes, like infrared and ultraviolet.
Telescope filters work like TVs and computer screens. They let you take images in red, green, and blue. Later, you stack the images in post-processing to create colorful views of Mars or nebulae.
Giant telescopes like Hubble and James Webb differ in how they take images, but both take filtered photos in ways amateur astronomers dream about. But don’t worry. You can still take stunning pictures and experience exciting visual observations using telescope filters in your backyard.
Telescope Filter Types
Some terms apply to different filters regardless of their desired use. For instance, you find differing wavebands across lunar, color, and light pollution filter types. Check out the details of the specific filter you select to ensure it fits your telescope or astroimaging camera and meets your viewing or photography needs.
Telescope filter designations come in narrowband, mid-band, and broadband to define how much light spectrum passes through. For example, Narrowband filters for imaging allow only a tiny portion of the light to pass through to your camera or eyepiece. Therefore, they work well with planetary and emission nebulae imaging.
But on the other hand, broadband filters are used for observing and allowing a broader spectrum portion through. They work best for galaxies, reflection nebulae, star clusters, and the Moon.
And finally, mid-bands fall in the middle. Therefore, they are suitable for observing and imaging various celestial objects, depending on your telescope and desired outcome.
These filters clip into your camera behind the lens bayonet and allow you to continue using standard lenses and adapters. Many different filters come in the clip style and are well-suited for astroimaging. Simply clip them in place before connecting your camera to your telescope.
Best Telescope Filters
Here are some types of filters and how they work best.
Telescope Filters: Light Pollution Reduction (LPR)
Living near a city means light suppression filters are an excellent investment. They reduce light pollution and boost contrast by blocking sodium vapor and mercury street lights. So that helps the skies look darker.
In addition to LPRs, you may also see light pollution reduction filters called City Light Suppression (CLS) and Ultra High Contrast (UHC) filters. And while there are differences in other functionality, they all reduce light noise.
Since light-reducing filters strengthen contrast, they create depth in your astroimages. Visual spectrums and H-alpha lines stream through while the filters reduce street light intrusion.
Lunar Telescope Filters
Earth’s moon is the brightest and nearest night sky object, so pointing your telescope toward it offers exciting opportunities for viewing and imaging. However, moon viewing gets tricky due to its brightness, so an excellent lunar filter lets you decide how much light to let through.
Lunar telescope filters reduce some glare so that other features are enhanced. Thirteen percent filters are standard, which means they only transmit 13% of incoming light. So your contrast gets a boost, and you can see more details.
You can buy lunar filter kits with varying light transmission selections, basic single moon filters, and variable polarizing filter options. The latter lets you adjust your light transmission level from 1-40% to decide what’s best for your target (moon or planet) in your current viewing conditions.
Telescope Filters: Solar
If you’ve ever dreamed about photographing a solar eclipse, you’ll need a high-quality solar lens to block UV and IR light. It also needs to block out a very high percentage of visible light due to the sun’s intensity.
Solar filters allow you to observe or image the Sun safely and join the ranks of citizen scientists to capture sunspot information and other solar data.
Of course, Sun observations and astroimaging should only occur with properly certified solar filters. So do your due diligence in verifying that your solar filter will protect your eyesight.
Celestron solar telescope filters are ISO 12312-2 certified for safe, direct Sun viewing. And another good choice is a solar filter from Thousand Oaks Opticals. The last 30 years have seen this Arizona company gain loyal followers for its quality.
Oxygen III (OIII) Telescope Filters
Oxygen III telescope filters are perfect for Deep Sky Object viewers and astroimagers. Emission and planetary nebulae come to life in fine detail. And you get a great dark background from the filter’s light blocking. So your nebulae images have an excellent contrast depth for spectacular results.
Optolong manufactures quality telescope filters amateur astronomers can count on. And this L-eNhance narrowband filter provides a dual bandpass for DSLR, CCD, and color CMOS astrophotography cameras.
Filters like Optonlong’s isolate OIII, H-Beta, and H-Alpha nebula emission lines with maximum transmissions of up to 90%. Even in light-polluted night skies, you’ll still get the prominent nebula color, RGB (red, green, blue.)
Telescope Filters: Color
Frederick Wratten (1840-1926) created the first colored filters for photography, so the color numbering system got his name. Wratten sold his company to Kodak, where you can still find a vast list of motion picture color filters.
So the question is, how do you know which color filter is best for which planet? And the answer is the best color filter that works for you is the best one for that planet. Not very helpful, right?
Remember that you can stack different filters together for the best result at your location and viewing conditions. But here’s a good guide for choosing a color filter for planetary viewing.
Remember the stained glass analogy; green light shines through green stained glass. So, for example, using a green filter highlights a planet’s natural green colors. Think about using an orange filter on Jupiter to make the gas clouds pop.
When you’re a new astroimager, it’s acceptable to buy affordable colored telescope filter kits like this one from Neewer. It gets strong Amazon reviews and helps you explore the night skies. Find out if this new hobby is for you before shelling out a lot of cash.
However, as you’ll find, spending a lot of money on filters is easy. So, over time, you’ll likely invest in several great multi-purpose options that cover your needs. For example, Astromania is a well-respected telescope accessory manufacturer with high-quality color filters among their products.
If your budget allows only one new filter, consider Celetstron’s UHC/LPR Filter. It reduces light pollution, increases contrast, and makes an outstanding contribution to your astronomy gear.