Which Filter Should I Use With an OSC Camera?
Astrophotography Guide
First published 19 March 2024
Last updated January 2026
Intro
I’m often contacted by beginners with questions about astrophotography, and one of the most common is which filters to use with a One Shot Colour camera. This guide is written to answer that question clearly, explaining the different types of filters available, when each one makes sense, and how to choose the right option based on your targets and imaging conditions.
A seemingly simple question…
I think that lots of beginners are expecting a simple answer to the question of which filter to use for their OSC camera. Normally the question will be something like, “I’ve got terrible light pollution, which filter is best?” As is the case with everything astrophotography-related, it’s a little more complex than you’d first think!
To begin with, let’s be clear that this guide is for OSC cameras, like my ZWO ASI 2600MC Pro. Mono is different as far as specific filter recommendations are concerned, although the background information we’ll cover is still relevant. Also, this guide is about deep sky objects (galaxies, nebulae, etc.) Planetary (like Jupiter, Saturn, the Moon) is quite different.
With that done, we can begin. Not all astronomical objects are the same. We can, in general, split them into two categories, based on the light that they emit. Knowing this is essential when it comes to filter choice. The two categories are broadband and narrowband.
Broadband
Broadband targets are those that emit lots of their light in the visible part of the electromagnetic spectrum. This is the part that our eyes naturally detect, and so do our camera sensors. The main types of broadband targets are stars (including clusters), galaxies, and reflection nebulae (clouds of gas and dust that we see because they’re reflecting the light from nearby stars). Here are three images I’ve taken of broadband targets:
Because our OSC camera sensors are naturally geared up for broadband targets, it’s not essential to use any filters to take good images of them. It can be beneficial, however, to use a UV/IR cut filter. This can help to produce sharper images, and reduce star bloat. Note that many astro camera, including my beloved ZWO ASI 2600MC Pro, have a UV/IR cut filter built in. If this is the case, you don’t need to buy an extra one. If you’re not sure about your camera, scout online and find some people that use the same type. They’ll be able to advise on whether you need a UV/IR cut filter.
You might be wondering about light pollution. By far the most effective way of combatting light pollution for broadband targets isn’t actually anything to do with filters. The trick is to gather lots of data and clock up a high total integration time. Think 20 or more hours from a city. This might sound unachievable, but with the right approach it’s not that hard. To help, I’ve written a whole article about how to get long integration times. Now, look again at the three broadband images above. They were taken from a Bortle 8 city centre, and I didn’t use any filters at all. Long integration times are the key!
There are lots of light pollution filters available, and given this article is about filters, I should mention them! It’s a bit of a minefield, and their effectiveness varies based on where you’re imaging from, and so your local sources of light pollution. I’ve tried lots and have only found one that actually provided me with any benefit: the Optolong L-Quad Enhance. I can’t say for sure whether it would work for you, because your exact sources of light pollution will be different from mine. Consider whether your money would be better spent on an accessory that makes it easier to achieve long integration times. Here are some ideas.
So, let’s sum up advice for broadband targets:
- You might see some benefit from a light pollution filter. Try different ones to test if they actually help. I’ve found the Optolong L-Quad Enhance to be the best for me, but what works for me may not work for you. And remember, there’s no substitute for long integration times.
- If your camera doesn’t have an in-built UV/IR cut filter, then consider one. Check in with other users of your camera for recommendations.
- Long integration times are key to beating light pollution. The worse your light pollution, the longer the required integration time.
- A light pollution filter is very much optional, even if you’re in the middle of a city.
Narrowband
Now let’s talk about the other type of target: narrowband. These give out most of their light in very specific wavelengths, hence the “narrow” in narrowband. The most common wavelengths are called Hydrogen-alpha (Hα), Oxygen-III (OIII), and Sulpfur-II (SII). Emission nebulae are excellent narrowband targets, and are plentiful in the sky.
If you were to treat such an object as a broadband target then you might be hard pressed to see any detail at all (other than the stars, which are broadband in nature). But capture the narrowband wavelengths and the target comes to life! The slider-view image below demonstrates this. Both pictures show the same target, but broadband is on the left and narrowband is on the right.
Narrowband wavelengths are quite distinct from the wavelengths that light pollution occupy, which is very useful for light-pollution plagued astrophotographers because if you can filter out everything except the key narrowband wavelengths, not only can we do justice to targets like emission nebulae, but we can also partly sidestep light pollution!
So, how do we go about capturing narrowband data using an OSC camera? That’s where filters come in. We OSC users commonly use dualband filters (although some triband ones are available). Dualband filters capture two narrowband wavelengths simultaneously, usually Hα and OIII.
There are lots of these Hα/OIII dualband filters available. The Optolong L-eXtreme was previously considered to be the best of these, but a newer generation has now been released. The Optolong L-Ultimate is the best I’ve used, but also the most expensive.
I mentioned that there are three main narrowband wavelengths: Hα, OIII, and SII. Most dualband filters cover Hα and OIII, so what about the SII? This wavelength is less common and often weaker in astronomical objects, so some OSC imagers basically forget about it and make bi-colour images using their Hα/OIII dualband filters. It’s also possible to create pseudo-SII from your data during processing, in order to create very colourful images from just Hα/OIII. It’s not as scientifically accurate as incorporating genuine SII data, but it looks striking!
It’s a good time to be an OSC imager though, as now there are some SII/OIII dualband filters available. These can be used if you want to create genuine Hα/OIII/SII images using an OSC camera. You collect data on your target using your Hα/OIII dualband filter, and then using your SII/OIII dualband filter. Combine the results during processing and hey presto, you have an Hα/OIII/SII image! The SII/OIII dualband filter I use is the Askar E2.
Mix and match
By now hopefully you’ve got a good grasp on the difference between broadband and narrowband targets, and how you should choose filters based on the specific target you’ve got in your sights. However, sometimes things are a little more complicated, and you may want broadband and narrowband data.
Let me give an example. I stated that galaxies are broadband targets, and that’s true. However, some galaxies have Hα regions (where stars are forming). Hα is narrowband, so are we missing out on it by treating the galaxy as only broadband? Let’s conduct an experiment to find out.
Below is a slider image of The Pinwheel Galaxy. On the left we see it imaged as a broadband target (with no filter). On the right is the exact same target, but imaged using an Hα/OIII dualband filter. (There’s hardly any OIII so we can ignore that). Notice how the broadband view contains lots of detail. The dualband view is nowhere near as impressive, but does highlight those areas of star formation in the galaxy’s spiral arms:
So what to do? As an astroimager, you have a decision to make. You could just stick with broadband data. Or, you could also collect some narrowband and add that in. The slider below shows these two options in fully processed form. On the left is broadband. These are often called RGB images (Red Green Blue). On the right is the RGB plus Hα; we call it an HαRGB image. Is it worth the extra time and effort of collecting the Hα? That’s for you to decide.
Here’s another example. I was recently imaging The Flaming Star Nebula. Some quick research showed that it’s both a reflection nebula (broadband) and an emission nebula (narrowband). Use the slider image below to compare my broadband image (Optolong L-Quad Enhance) on the left, with Hα/OIII (Optolong L-Ultimate) on the right.
Here’s what the two images look like combined: an RGBHαOIII image:
And finally, just when you thought you had it all figured out, let’s mention star colours. Stars are broadband targets, although they’re so bright that they show up in narrowband too albeit not as well. Their colours, however, are lost when imaging in narrowband, and they all appear as white dots. Broadband captures star colours well. So, if you want to image a narrowband target but have accurate star colours, then you may want to add a little bit of broadband data just for the stars. This is all comes together when you process the image.
Here’s a final example photo. It’s the Cygnus Wall captured using an Optolong L-Ultimate (Hα/OIII), Askar D2 (SII/OIII) and a little bit of broadband (no filter) just for accurate star colours.
Summary
Phew! That’s a lot of info to take in. See how the question “which filter should I use?” is actually quite complex? Let me sum up the advice:
- If you have an OSC camera but no spare budget, then you can still image broadband targets with no filter at all (or just a UV/IR-cut filter if necessary).
- A broadband light pollution filter may be beneficial, but you won’t know for sure until you test it under your local sky conditions. I use an Optolong L-Quad Enhance. I consider a broadband light pollution filter to be a low-priority purchase as you’ll probably get more bang for your buck by spending money on accessories that make it easier to get long integration times.
- The worse your light pollution is, the longer your total integration time should be. This is particularly true with broadband imaging.
- If you want to image narrowband targets — which I recommend, because they’re plentiful, interesting, and narrowband works well even under light-polluted skies — then first buy an Hα/OIII dualband filter. The best premium option is, in my opinion, an Optolong L-Ultimate.
- If you’re confident with Hα/OIII and want to develop more advanced skills then the next logical step is to buy an SII/OIII filter. I use an Askar E2.
- Choose your filter based on your target. Do some research to find out what type of object it is. Galaxy? Emission nebula? Globular cluster? Reflection nebula? This will inform your filter choice.
- I use an Optolong L-Ultimate (Hα/OIII), Askar E2 (SII/OIII), and Optolong L-Quad Enhance (broadband RGB).
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I read a new article about filters. You explained it very clearly so I was able to understand it well. In the end, I had L-eNhance, but I additionally purchased Optolong L-Quad Enhance. I really liked the image you introduced in the article that combines the image obtained through Optolong L-Quad Enhance and the g increase obtained through Optolong L-Ultimate, so I would like to challange the next clear sky.
Awesome website, thank you! Really helpful that everything you write about is for OSC users.
I’m using an ZWO FF107/AM5 with an ASI2600MC-Duo in a Bortel 3/4 zone. I’m very happy with how everything works overall and now I want to add some narrowband filters for nebulae.
I can’t use an Optolong L-Ultimate filter as the 3nm bandwidth would be too dark for the integrated guide camera in the ASI2600MC-Duo.
Instead, I’ve been advised to try an Optolong L-eXtreme (Ha/OIII) filter with a 7nm bandwidth.
In the future, I’d like to also try a SII/OIII filter, so the Askar D2 looks like a great choice from this article.
Do you have any opinions about using (i) an Optolong L-eXtreme with an Askar D2 vs (ii) an Asker D1 with an Askar D2?
Not sure if there are any advantages to sticking with the same brand for both? (especially since the L-eXtreme is 7nm and the Askars are 6nm).
Hi David, thanks for your comment and your donation! My question to you is, are you sure the L-Ultimate makes the view too dark for your camera’s integrated guide camera? I haven’t tried this combo, but I suspect the guiding chip would still be able to find a fair few guide stars. Fair enough if you’ve spoken to people that have tried it and say it doesn’t work — personal experience trumps my gut instinct! In that case, I’d recommend an Askar D1 over an Optolong L-eXtreme; the narrower bandpass is a benefit, but even more useful is the Askar’s much-improved control of halos around bright stars. That was always a real annoyance with the L-eXtreme. You can read more about these filters here: https://urbanastrophotography.com/index.php/2022/10/22/dualband-filter-shootout-l-extreme-vs-l-ultimate-vs-colour-magic-6nm/
Hello and congratulations on the site. I should buy my first narrow band filter to use with the L-Quad Enhance that I own and I am undecided between the l-ultimate and the l-Para. I would use it under a bortle 6 sky with Skywatcher Newton 200/800, Skywatcher newton 130 pds and Asi 533 pro and also Samyang 135 F2 that I use with a Canon. Thanks and have a nice day
Hi Marco, the L-Ultimate is in principle the better filter, with its 3nm bandpass compared to the L-Para’s 10nm. However, the L-Para is better for very fast optics such as your Samyang. So, the L-Ultimate would be best for your two Sky-Watcher telescopes, while the L-Para would be best for your Samyang. It’s a tough decision!
I am retired from Steward Observatory Mirror Lab as the Supervisor of the Polishing Lab. I know how to make mirrors, but I didn’t know how to use them. I am currently using a ZWO ASI533MC Pro OSC camera. While I have taken many pleasing images your explanation, mixed with your excellent “slider” examples, has convinced me to start using narrow-band filters. In particular is M33 that I image adequately with an L-eNhance filter, I can never seem to grab the Ha that adds so much character to the image. Now, thanks to you, I know how to do that. Of all tutorials and informational articles I have read, yours is unquestionably the best. I have added your site to both my imaging AND processing folders for ready referrals. I am about to enter a whole new world of imaging thanks to you.
Thanks Patrick, this is a lovely message to read! I hope you continue to find the the content here useful.
Hello Lee…… I have read some of your articles and enjoy your splendid photographs……I am a beginner in astrophotography, using my 5 inches Celestron reflective telescope and my Sony A6500 DSLR….
I use an UHC filter for my photos on Bortle 5-6 sky with 30-35 Celsius degrees in environment temperature, and some LED lights pollution…..is this filter advisable on these conditions ….do you think a narrow band or the mix broad and narrow band filters would help me to improve my photos and to eliminate the LED light spots on the photos….or the long integration times …?
Anyway, I have a long road to walk, and I thank you for share your knowledge….
Hi Francisco, I haven’t used an UHC filter before so don’t have firsthand experience. I’m sure you’d see a big improvement if you could upgrade to a cooled astrocamera. For broadband targets just aim for long integration times.