If you shoot your astrophotography images with a color camera in the city, there is a good chance that light pollution filters can make your life a little easier.
By ignoring specific wavelengths of light in the visible spectrum associated with artificial light sources such as a streetlamp. The best way to test if a particular filter is a good fit for your skies is to review examples taken by others from similar conditions.
A quality light pollution filter will allow the important colors and light emitted by your astrophotography subject to reach the camera sensor, without the nasty brown glow of a washed-out sky. The design of the filter includes layers that block specific bandpass lines of the visible spectrum.
When it comes to collecting great data from your color camera, there is no substitute for dark skies. However, the light pollution filters talked about in this post may make astrophotography from the city a little more practical and rewarding.
Why I Use Light Pollution Filters
I rely on light pollution filters to take astrophotography images from my backyard. They help ignore the bright city sky where I live and collect images of objects in the night sky with better contrast between my subject and a brown sky.
Not everyone agrees that using a light pollution filter for your camera is the best way to do astrophotography, but depending on where you live, it might be the only way to go.
In this post, I’ll share several examples of astrophotography filters being used on a variety of deep-sky objects from the city. I asked the incredible community on the AstroBackyard Facebook page for some example images, and they delivered big time.
IC 1396 captured from the city using an Optolong L-eNhance Filter.
Types of Light Pollution Filters
There are probably over 100 different light pollution filters available today. The bandpass allowances vary widely, but there are essentially two main types of light pollution filters for color cameras; broadband filters (broad-spectrum, multi-broadband), and multi-narrowband filters.
Broadband filters are used to capture more natural-looking images of objects in the night sky, at the expense of allowing a little artificial light through as well. Multi-narrowband filters aggressively ignore most wavelengths of light in the visible spectrum, allowing narrow bandpasses of light in key areas to pass through.
The type of camera you use for astrophotography will determine the right light-pollution filter for you. For example, a stock DSLR camera will be much less effective when paired with a multi-narrowband filter. This is because a key bandpass for these filters is hydrogen-alpha (656nm).
I Use Broadband Filters For:
- The Milky Way
- Star Clusters
- Reflection Nebulae
- True-Color Images (Particularly focusing on the stars)
- Meteor Showers
- The Moon
I Use Multi-Narrowband Filters For:
- Emission Nebulae
- Supernova Remnants
- Planetary Nebulae
It’s worth noting that I also shoot unfiltered in certain situations where a broadband filter would help. This often leads to a more challenging image processing session, but the results are usually worth it.
Real Examples from Amateurs
I know you can just go to the company websites for mind-blowing example images with these filters – but maybe we should take a look at what actual amateurs are doing from the backyards?
Before we get started, I should mention that the effectiveness of a particular light pollution filter will depend on your imaging location. You can find out the Bortle Scale class of your home using a light pollution map, or my favorite, the ‘Clear Outside’ mobile app by First Light Optics.
My backyard is considered to be a class 6-7, the introduction of LED street lights throughout my city over the last few years has brightened the sky up significantly. I appreciate that they are full cut-off lights pointing directly downwards, but what can I say, when you look up you see fewer stars than ever before.
The filters I’ll talk about in this post are primarily used with color cameras. So, DSLRs, mirrorless, and one-shot-color astronomy cameras. These are astrophotography filters that let you capture a “complete” color image in one shot. They are not narrowband filters that collect data in one wavelength of light at a time.
Essentially there two types of filters, broadband and narrowband, and they are exactly how they sound. Broadband filters collect a wide array of light wavelengths and can produce more natural-looking colors (especially the stars). Whereas narrowband filters isolate a very specific bandpass only but ignore much more light pollution and moonlight.
I have included multi-bandpass narrowband filters, as they can often create impressive “near” full-color images in one shot (with some processing). I guess you could call this category, one-shot-color light pollution filters.
A 2-inch round mounted Optolong L-Pro filter.
Modified Camera or Dedicated Astronomy Camera
Most of the images I am about to share were captured with cameras with increased sensitivity to the hydrogen-alpha wavelength at 656 nm. (A lot of the great emission nebula really shine here).
If you’re on the fence about getting a dedicated astronomy camera or modifying your DSLR, the images I am about to share may push you over the edge.
The light pollution filter should list whether it was designed for a stock or modified camera in the description. The biggest thing to remember here is that a stock DSLR or mirrorless camera will have the internal UV/IR cut filter intact, whereas a full-spectrum modified DSLR like my Canon EOS Rebel T3i, it was removed.
Filters such as the Astronomik CLS-CCD include an added IR layer for this reason.
The Great Light Pollution Filter Round-Up
All of these filters will have a spectral graph on their website showing you where they allow light to come through, and where they don’t. Understanding the type of artificial light glowing above your backyard will help you make a smart decision on a filter.
You’ll need to make sure you purchase the correct format for your particular camera body, whether it will be attached to a telescope, or used with a camera lens.
A clip-in DSLR filter will sit underneath most camera lenses.
Clip-in models are great for camera lens work, while 2″ round mounted versions are great for threading into your telescope flattener or filter drawer.
As far as camera bodies go, Canon seems to have the widest variety of options available. More and more Nikon and Sony DSLR and mirrorless bodies are being used for astrophotography, and I expect the availability of astrophotography filters to follow.
For example, if you have the old-school, yellow, sodium vapor lamps lining your street, make sure to get one of the many light pollution filters that block this glow (I believe it’s around 589nm).
I can’t tell you which light pollution filter is best for your needs, but hopefully, the examples shown in this post will give you a better understanding of what to expect.
SkyTech L-Pro Max
The Triangulum Galaxy by Stacey Dowton.
This beautiful photo of the Triangulum Galaxy was captured by Stacey Downton in the United Kingdom. Stacey shares her personal astrophotography on YouTube (AstroStace), and I am a fan of her dedication and impressive images.
The SkyTech L-Pro Max was designed for moderately light-polluted areas, although many are using this filter under some bright skies. The SkyTech variation shares a striking resemblance to the Optolong L-Pro, which you will see a lot in the filter world.
This is a true broadband filter that aims to preserve the natural colors of stars in the night sky. It includes a mild filter against known sources of artificial light including LED street lights. Here is another excellent example of what is possible with the L-Pro Max filter:
The Andromeda Galaxy by Ross Clark.
Broadband targets such as galaxies and reflection nebulae are some of the most difficult targets to capture from the city, and the images above are a testament to the practicality and performance of the SkyTech L-Pro Max.
As I mentioned above, the Optolong L-Pro has a remarkably similar spectral graph to the SkyTech variation. I would expect a head-to-head test from the same imaging location to produce identical results (If you’ve tested this, please let me know in the comments).
The following image of the Iris Nebula was captured using a ZWO ASI294MC Pro from my Bortle Scale Class 6/7 backyard using the Optolong L-Pro filter.
The Iris Nebula by Trevor Jones.
I have personally used the Optolong L-Pro filter (see my video review) when imaging from my light-polluted backyard and was very happy with the results. Whether I used my DSLR camera or a dedicated astronomy camera, the stars were a little red in the individual exposures.
This is very typical of a light pollution filter as one of the primary light wavelengths they are blocking is in the brown, orange range. However, it is possible to bring those red stars back to their natural color (whether blue or yellow) using some simple techniques in Adobe Photoshop.
A single test exposure with, and without the L-Pro filter in place.
Comparing the transmission graphs of each light pollution filter against each other is a great way to help you decide which filter is right for you. The Optolong L-Pro filter has a very interesting bandpass selection, as you can see from the wavy transmission line with 5 humps shown below.
Each one of the 4 major dips are known sources of artificial light pollution that have been selectively blocked by the filter.
The next filter is less selective (more aggressive) in its light-blocking abilities, resulting in a less natural, but higher contrast image.
This light pollution filter has been around for a long time and is a favorite among amateur astrophotographers shooting with a modified DSLR camera. The CLS-CCD version (unlike the “CLS” version), includes an additional IR layer for cameras that have had the stock UC/IR cut filter removed during modification.
I personally found this filter to be one of the most useful options when shooting emission nebulae targets from the city. Unlike a milder filter such as the L-Pro, the Astronomik CLS-CCD is more aggressive and creates a strong contrast between the nebula and a bright sky.
Here is an excellent example of this filter in use by Niek Damen on the Heart and Soul Nebulae.
The Heart and Soule Nebulae by Niek Damen.
Niek mentioned that he uses this astrophotography filter on his DSLR that was modified with a clear glass replacement he performed himself. There are many affordable DSLR’s kicking around in the used market, both modified and stock.
If you own a Canon EOS Rebel series DSLR with the full-spectrum “naked sensor” mod, this is the filter for you.
Here is another excellent example image by James Crouch in the constellation Orion.
Orion Nebula region by James Crouch.
In my experience, the aggressive light-blocking properties of the Astronomik CLS-CCD filter can result in images with an overly red cast, particularly noticeable in the stars.
The red stars can be corrected during the image processing stage in a number of ways. I like to dig into the red channel of the image and make sure that the stars are not larger here than they are in the other channels.
Another method is to use the defringe sliders found within Adobe Camera Raw under the lens correction tab.
After observing the transmission graph for this filter, it’s easy to see why the images have much more contrast straight out of the camera than the Optolong L-Peo. This filter is aggressively blocking all areas of the visible spectrum except two intentional humps in the 500 to 650nm regions of the visible spectrum.
You may be surprised to see this filter talked about on this list. To be honest, the only reason I’ve included the Svbony CLS filter is that I realized that many people are using this filter (and similar generic-branded filters) around the world.
The Svbony products are available on Amazon, and I myself have purchased affordable “no-name” filters for astrophotography in the past. Without having sufficient data to test myself, I would be very surprised if the Svbony wasn’t a clone of the original Astronomik CLS filter.
Here is a useful test image from Russell Hippert of the Dumbbell Nebula using the Svbony CLS filter from a Bortle Class 8/9 sky. Russell mentioned that his city does not currently have any lighting ordinance, and that broad-spectrum intrusion from reflections is very high.
The Dumbbell Nebula by Russell Hippert.
These filters are worth giving a shot. I purchased a complete set of 1.25″ Svbony filters to use with a Starlight Xpress SX-42 and was astonished by my results on the Fish Head Nebula. Here is an interesting comparison on Cloudy Nights of the Svbony CLS filter against the Optolong L-Pro.
Astro Hutech IDAS LPS D1
Astro Hutech knows what they are doing when it comes to light pollutions filters. The first astrophotography filter I ever purchased was the IDAS LPS D1, and I used it extensively for my first 4-5 years of imaging.
The IDAS LPS (light pollution suppression) filters are another popular choice for amateur astrophotographers shooting from the city, and for good reason. They include a unique IGAD coating for durability and offer a range of options for your specific sky profile (see this IDAS LPS filter chart)
Here is an image shared by Tomáš Zábranský from the Czech Republic using the IDAS LPS D1 filter under Bortle Scale Class 5 skies.
The Elephant’s Trunk Nebula by Tomáš Zábranský.
Here also shared this fascinating test image showcasing the differences in the image from Bortle Scale Class 3-5 sites using a modified Canon 700D. Notice how the image increases in brightness significantly as the city light pollution increases. If you think about what had to take place for the following comparison to take place, you’ll appreciate Tomáš sharing the results.
Here is a look at the transmission graph for the IDAS LPS D1 to compare with the other filters in this post.
Astro Hutech IDAS LPS D2
The IDAS LPS D2 is said to do a better job of blocking the modern white LED lights found in the city. This is an attractive feature for anyone who’s street has “upgraded” to energy-efficient LED’s.
I have not tested the IDAS LPS D2 myself, but I was very impressed with the following image shared by Kevin Lewis on Facebook. This is the Horsehead Nebula, Flame Nebula, and Orion shot in broadband RGB with a stock (non-modified) DSLR camera.
Orion’s Belt by Kevin Lewis.
The image above was taken using a stock Canon 5D Mark IV DSLR with the IDAS LPS D2 filter in action. It’s interesting to note that the natural blues of Orion have been acquired, and the light pollution from Kevin’s Bortle Scale Class 5 skies have been kept at bay.
Astro Hutech IDAS Nebula Booster NB1
The IDAS Nebula Booster shares a similar profile to the popular Optolong L-eNhance filter. It collects light in two primary areas of the visible spectrum, H-alpha, and OIII.
The image shared by Tony Lanahan below looks remarkably similar to my version of the Heart Nebula taken using the L-eNhance. Having another option in this category of filter is great news for amateur astrophotographers, as it seems dealers often have a hard time keeping them in stock.
The Heart Nebula by Tony Lanahan.
The most impressive aspect of the image above is perhaps that it was captured from the edge of Chicago, a massive metropolis of light. I think you’ll find multi-bandpass nebula filters in general to be a lifesaver from city skies.
As you’ll see in the transmission graph below, the IDAS NB1 actually collects some data in the subtle SII wavelength as well. Combining all of the narrow bandpasses together can result in some dynamic images using a color camera.
IDAS NBA (Nebula Booster) transmission graph.
Since reviewing the Optolong L-eNhance filter in July 2019, I have taken almost a dozen impressive images with it. Fantastic new results are popping up daily with the L-eNhance, and I think it is safe to say this filter is a winner with color cameras.
The image below is the perfect example of what the Optolong L-eNhance filter was designed to do, as you can clearly see the light in Ha and OIII in this area of the night sky revealed.
The Flaming Star and Tadpole Nebula by Chad Robert.
The picture above was taken using a ZWO ASI294MC Pro camera through a William Optics GT81 APO telescope. The imaging location was a Bortle Scale Class 5/6, which makes the image even more incredible. The combination of a cooled CMOS astronomy camera and the L-eNhance is tough to beat.
When comparing the transmission graph of the Optolong L-eNhance with the IDAS NB1, it is interesting to note that it looks as though the cutoff after the Ha (656nm) bandpass line is steeper on the L-eNhance. In theory, this could result in higher contrast images, looking slightly less “natural” in terms of overall color.
Optolong L-eNhance transmission graph.
Update, August 2020
The Optolong L-eXtreme Filter has launched, and many amateur astrophotographers agree that it is an improvement over the L-eNhance. This version of the filter isolates the OIII bandpass at 7nm, without including H-Beta, and the small bandpass between OIII and Hb.
The resulting images appear to be more dynamic with better contrast. The following image of the Veil Nebula was captured using the Optolong L-eXtreme filter and a QHY268C one-shot-color camera.
The Veil Nebula. Captured using the Optolong L-eXtreme Filter.
Astro Hutech NGS1 Night Glow Suppression
Here is another broadband light pollution filter for you to consider. The Astro Hutech Night Glow Suppression filter was designed to capture the natural colors of your subject while carefully ignoring the biggest culprits of man-made light.
Have a look at the transmission graph of this filter to better understand just how specific these areas of the visible spectrum are. The colors represent the areas of light associated with Ha, Hb, OIII, and SII gas.
For a real-world example of this filter in action, have a look at the following image captured by Callum Wingrove of the Pleiades Star Cluster from a Bortle Scale Class 8 sky.
The Pleiades by Callum Wingrove.
Reflection nebulae can be difficult to do justice from a Class 8 sky, and Callum’s image proves that it is still possible with the right approach. I used the IDAS NGS1 filter to photograph the Cocoon Nebula with my DSLR camera, and I was extremely impressed with the way it handled star colors.
For subjects like this, you have the power to create contrast in the emission nebulae, and a filter that captures natural-looking star colors in a single shot.
The Cocoon Nebula by Trevor Jones (IDAS NGS1 filter).
Radian Telescopes Triad Ultra
Everyone likes to point out how expensive this filter is, and I understand why. It’s hard to ignore the fact that the Triad Ultra filter surpasses the $1K mark.
Price aside, the Radian Telescopes Triad Ultra filter is a really exceptional choice. I had a chance to demo the Triad Ultra filter in the summer of 2019 and ended up capturing some of my favorite images of the year.
Here is one of the images that stood out, it’s the Sadr region in the constellation Cygnus using a Canon EOS 60Da DSLR.
The Sadr Region in Cygnus by Trevor Jones.
Andy Robertson shared an impressive image of the North America Nebula on the AstroBackyard Facebook page that was hard to ignore. If you are looking to separate the color channels of your one-shot-color image for a false-color version in another pallet, the Triad Ultra may be worth looking into.
The North America Nebula by Andy Robertson.
Have a look at the distinct 4 bandpass transmission lines of this filter on the graph.
Baader Moon and Skyglow
Lastly, we have the Baader Moon and Skyglow filter. I experienced some early success with this broadband filter when I used my first dedicated astronomy camera (Altair Hypercam 183C). Have a look at how this mild light pollution filter recorded the colorful stars in this image of the Ring Nebula in Lyra.
This photo was taken from a Bortle Scale Class 8 backyard, and the natural colors the filter allowed to pass through is commendable.
The Ring Nebula by Trevor Jones
Here is a look at the Triangulum Galaxy in broadband RGB using the Baader Moon and Skyglow filter from a Bortle Scale class 4 site by Godfried Nijs. This photo was captured using a ZWO ASI294MC Pro color camera through an 8″ Celestron CPC 800 SCT telescope.
If you are not sick of looking at transmission graphs for astrophotography filters yet, here is a look at where the Baader Moon and Skyglow filter selectively allows light to pass through.
If you a looking for some specific advice on choosing the right light pollution filter for your needs, you should first know that the answer to that question depends on your unique imaging location.
For example, if you are living in a neighborhood with yellow sodium vapor lights dotting the streets, you will likely experience different results than I do from my glowing “blue-white LED” backyard.
I can give you some general advice though, based on my personal experience imaging from a Bortle Scale Class 6/7 backyard.
I found the Optolong L-Pro and Astro Hutech IDAS NGS1 to be particularly effective at achieving broadband color images from home. Heck, the L-Pro even did a good job at capturing broadband targets from my last house (a Class 8).
I believe that the greatest test of a broadband RGB filter from the city is its ability to record natural-looking star colors, particularly the blues and yellows. The IDAS NGS1 blew me away when I photographed the Cocoon Nebula this summer.
As for a multi-bandpass filter, the Optolong L-eNhance has proven to be one of my greatest allies when capturing nebulae from the backyard. It manages to harness the power of a narrowband filter while capturing color images in a single shot.
The Cave Nebula by Trevor Jones (Optolong L-eNhance).
With careful image processing, these images can be adjusted to achieve a “near normal” looking color balance. Blend in some data shot using a broadband filter for star color, and you’ve got an impressive RGB image.
No matter which light pollution filter you choose, remember that your final result depends heavily on your image processing skills, and how you manipulate the data. The images do not come directly out of the camera as you see them in this post.
However, a light pollution filter that is a great fit for your skies will make the task of processing the image much easier and more enjoyable.