Have you struggled to see clear images of nebulae, galaxies, clusters, and distant stars with your telescope before?
It's not a surprise. Light pollution, poor seeing and the limitations of your telescope conspire to give distorted, blurry, or dim images of distant celestial objects...
Sooner or later, all backyard astronomers discover they need to buy a filter to improve their viewing or astrophotography results.
If that's you, we're going to help you find the right telescope filter to help you out. In this article, we’ll take a look at the best telescope filters on the market for deep sky objects. (If the moon is your thing, click here for our guide to lunar filters).
Best Telescope Filters - Quick Comparison
General use, smaller scopes
Sharp image contrast
Longer viewing periods
At the end of this article, you'll find our more detailed reviews. You can also click on the links in the table above to check prices and customer reviews on Amazon.
Why Should I Use a Telescope Filter?
A coffee filter removes the grounds from the coffee so you can enjoy the full flavor of your cup without unwanted bits creeping in. In much the same way, a telescope filter removes unwanted light from your eyepiece so you enjoy the full deep sky object experience.
Telescope filters are the same size as your eyepiece (1.25” / 2”) and screw onto it. Their job is to stop light that makes an object look worse from reaching your eye. All that's left is the light from the object itself. This improves the object's contrast, making it ‘ping’ out of the eyepiece. In turn, your backyard astronomy experience is drastically improved.
There are three general classes of telescope filters which improve the viewing of deep sky objects (DSOs):
- Light Pollution Filters
- Narrowband Filters
- Line Emission Filters
Light Pollution Filters
Light pollution filters are broadband. This means they let most of the light entering your telescope reach your eyes.
What they remove are light wavelengths associated with street light pollution. They are most effective against sodium and mercury vapor light coming from older streetlights.
Sadly, the newer LED streetlights emit light across the whole visible spectrum, so light pollution filters are not effective against them.
Narrowband filters are more discerning; only allowing a few wavelengths of light through.
The light from nebulae comes from the gases that form them. So, if you filter out the light of all other wavelengths, you're left with just the nebulae. This gives phenomenal contrast and improves the view.
These are more expensive filters because they are more refined.
Line Emission Filters
Finally, at the most expensive end, are the line nebula filters.
These, as the name suggests, only allow a single wavelength of light to pass through. Most typical are filters for OIII, H-Alpha and H-Beta (oxygen 3, hydrogen alpha, and hydrogen beta).
An OIII filter only allows two precise wavelengths of light through, both associated with OIII. (https://en.wikipedia.org/wiki/Doubly_ionized_oxygen). In practical astronomy terms, these are nebulae with green, turquoise and cyan colors.
Hydrogen-Beta is a single wavelength of blue emitted by a hydrogen ion. (see the picture of lines below, showing H-alpha, etc).
Hydrogen Alpha is the red line in the picture and causes red/pink nebulae like the infamous Orion Nebula
How to Use Telescope Filters for Best Results
To get the best results from your telescope filter, remember these simple guidelines. [list?]
When you start using them, begin with lower power and take in the scenes of beauty that you won't have captured before.
Many filters improve viewing in light-polluted skies, but they have an even more dramatic impact in dark locations.
Filters work best when your eyes are dark adjusted, and you'll see better detail using averted vision.
These next six filters are our recommendation for some of the best telescope filters for deep sky objects that you can buy today.
Six Best Filters for Deep Sky Objects
The following six filters are ones that we believe offer the best options for beginners with light pollution and those wanting to improve their nebulae experience.
The final one (Celestron's Narrowband OIII filter) is for the serious amateur who already uses filters but wants a more 'grown-up', specialist filter.
The largest challenges to viewing deep sky objects are light pollution and atmospheric refraction.
These both easily drown out distant targets. For this reason, Orion’s UltraBlock NarrowBand filter can be a boon to your astronomy.
The UltraBlock NarrowBand filter helps remove light pollution because it only allows light with the frequency of H-Beta and OIII to pass through. As a result, you'll see increased contrast in your telescope image.
Many nebulae shine in these wavelengths, so only letting these frequencies of light pass to your eye means you should see nebulae much more easily.
This is a 1.25" filter and is, in our view, the best 'all round' filter.
If you can only afford one telescope filter, then this one is ideal. It will give you better contrast that with a light pollution filter and cost less than individual OIII and H-Beta filters.
- Narrowband pass
- Good contrast
- Good pollution blocking
- Designed for nebula viewing
- Great 'all-rounder' filter
- Bandpass may be too narrow for general use
- Contrast improvement may lose dim objects in the background
- Better filters on the market for specialist needs
The Orion 2-Inch SkyGlow Filter is a cousin of the UltraBlock NarrowBand. The difference is that this is a broadband filter designed to block local light pollution to improve general deep sky object viewing.
You might think this makes the 2-Inch SkyGlow a worse filter, but that’s far from the case.
Though the 2-Inch SkyGlow doesn’t block as much local light as its more narrowband cousin, it’s much friendlier for general purpose use. As well as DSOs, you can use it to improve viewing of non-deep sky objects in moderately light-polluted skies.
You’ll find the 2-Inch SkyGlow filter very user-friendly. Narrowband filters often block out other objects from view but, because the SkyGlow is broadband, that won't happen with this filter.
If you need a light pollution filter, a deep sky object filter, and a planetary filter, you could get away with buying only the 2-Inch SkyGlow filter for now.
- Combines well with other filters
- Performs with non-deep sky objects as well as DSOs
- Blocks some light pollution
- Broadband bandpass
- No image distortion
- Won't block city-level light pollution
- Not light efficient in all setups
- Doesn't improve image contrast
This Orion broadband eyepiece is the 1.25-Inch counterpart to the 2-Inch SkyGlow Broadband Filter. Use it to manage suburban levels of light pollution without blocking light from objects you’re interested in seeing.
The filter advertises itself as ideal for viewing nebulae, galaxies, and star clusters, all which it does well.
But, there's another advantage to this filter:
Because it's 1.25-inch, it’s probable that you’ll be using it with a less powerful telescope than its larger cousin. So Orion has made sure it works well with closer objects, too.
To be clear, this isn’t a lunar filter —distant objects are its specialty—but it’s a more forgiving filter for closer objects than one might suspect. In a pinch, you could use this filter for general purposes in a light polluted environment.
- Blocks most light pollution
- Performs with non-deep sky objects as well as DSOs
- Combines with other filters
- Useful for smaller scopes
- Easy to use
- Not as good at producing a deep sky image as dedicated filters
- Not light efficient in all setups
- Doesn't improve image contrast
The Astromania Ultra High Contrast Filter is an intense option for astronomers interested in imaging nebulae.
The narrow filtering of the Astromania UHC increases the perceived darkness of space, which causes lighter objects like nebulae to stand out even if they’d be dim otherwise.
You can use this filter in a light-polluted environment, but it excels in areas of low light pollution. Here, the contrast between space and the background light is even greater, so this filter delivers awesome results.
Each Astromania UHC filter is individually measured and inscribed with the percentage of light it allows to pass from the hydrogen-beta and oxygen-3 emission spectra.
Whilst there’s little filter-to-filter variability, you can see at a glance your own filter’s performance. This can help you determine how much light you’ll be losing when combining it with other filters.
This filter is for serious nebula viewing. To get the best from it, have light discipline with your night vision: get well dark-adjusted and use averted vision.
- Each filter individually measured
- Superior image quality for nebula viewing
- High contrast
- More light sensitive than other filters
- Not suitable for near-sky
- Too specialized for beginners
Celestron’s Ultra High Contrast Light Pollution Reduction Filter is another great option for dealing with suburban levels of light pollution. It increases the contrast of your telescope’s image so that you can view nebulae or galaxies with ease.
This filter has a feature which the other light pollution reducing filters don’t: a bandpass optimized for “natural” viewing.
By “natural” viewing, Celestron means it increases the sharpness of contrast between the darkness of space and the objects in your image without creating harshly distorted edges. This can happen with overly-narrow, aggressive bandpass filters.
This means Celestron’s UHC/LPR isn’t as discriminating against the light that falls outside of its bandpass. However, the set-off to that is this filter is going to be easier on your eyes.
Celestron’s choice to slightly broaden the bandpass is a nod a reality of backyard astronomy. Everyone's balance of light pollution, night vision and setup quality is different.
The wider bandpass is a well thought out technical concession in the name of user experience. You’ll appreciate the added eye comfort it provides during a long night spent peering at distant nebulae.
- Provides an image that's easy to stay focussed on for a long time
- Good light pollution reduction
- Great for long periods of deep sky observing
- Slightly wider bandpass means lower contrast
- Does not increase darkness of space, increases clarity of objects
Celestron’s Narrowband Oxygen III 1.25 inch filter is a nebula-dedicated filter with an ultra-narrow bandpass. As noted in its title, the bandpass is only oxygen-3 spectra.
Because it lets so little light through, this filter is best used in a dark sky location and with a larger aperture telescope. Anything below 6-8" aperture will not let enough light in to make full use of this filter.
It's narrow bandpass will make stars seem to disappear, leaving only certain planetary nebula, like the ring nebula in Lyra, (and a few diffuse nebulae) visible.
To get the best from it, make sure your scope is in position before you screw it in place, as your reference stars will disappear from view when you do.
Also, be sure to use lower power to get going and only zoom in when you've found it and want to pull out more detail.
Whilst this limits the range of objects its useful for, it is tough to beat the images produced with this filter.
- Specializes in OIII observation, giving increased clarity there
- Good contrast in low light pollution
- Great choice for the right kinds of DSO
- Weak light pollution removal
- Not helpful for near-sky objects
Your deep sky object filter needs will vary depending on where you live and how willing you are to travel to a darker area. For this reason, Orion’s 1.25 Inch UltraBlock NarrowBand Filter is right for most amateur astronomers interested in casual nebula viewing with the least hassle.
You’ll still have to be attentive to the filter’s bandpass when viewing things which aren’t nebulae, but you’ll get a large efficiency bonus by combining your bandpass filter and your light pollution reduction filter into the same unit.
As runner-up, Celestron's LHC LPR filter is also a great choice. It nods to user experience as an important feature to bring to the table, unlike any of the other filters we’ve mentioned here.
If you already have a general purpose filter and are looking for something more 'grown up', we recommend trying the Celestron Narrowband OIII. Just keep in mind that it works best in darker skies with a bigger scope.
The filter you choose for deep sky object viewing may seem like a major choice to make but don’t worry too much about picking the 'right' one.
All the filters we’ve mentioned here are great choices, but the most important choice for you to make is to be serious about viewing deep sky objects.
Product images sourced from Amazon.com