If you shoot in light polluted skies with a DSLR, listen up. I’ve recently got my hands on an affordable new astrophotography filter for my Canon T3i.
Whether you shoot with a modified camera through a telescope or a stock DSLR with a camera lens attached, a light pollution filter will help you shoot longer subs. Longer image exposures mean a deeper view on your subject.
The SkyTech Canon EOS Clip Filter
In the past, I have used light pollution filters such as the Astronomik CLS, and IDAS LPS clip-in models on my Canon DSLR. In this review, I will be testing 3 filters from SkyTech that are designed to block out light pollution, and allow you to partake in astrophotography from the city.
This review is most valuable to those shooting deep sky astrophotography with a modified DSLR from a light polluted location.
If your exposure time is limited to under 2 minutes due to a washed out city sky, I feel your pain. Images shot in my backyard without a filter on my 600D are completely white after a 120-second sub at ISO 1600.
Astrophotography Light Pollution Filters
SkyTech offers clip-in filters for Canon EOS DSLR’s in several different imaging situations. Each has their own characteristics to perform best based on your imaging location and conditions.
For instance, the LPRO Max filter is designed for wide angle landscape astrophotography and produces more natural looking star colors than traditional UHC or CLS filters. This design lets more overall light in but renders the colors in the Milky Way more accurately.
This line of SkyTech LP filters was designed for use with APS-C sized Canon EOS cameras such as the Canon Rebel series. Each SkyTech filter uses polished Schott glass in a precision laser-cut housing. The clip-in design fits securely over the sensor of your Canon camera.
SkyTech CLS (City Light Suppression) Filter
The CLS filter was designed with a unmodified DSLR camera in mind. As opposed to a UHC filter, the CLS filter has a wider band-pass to produce more natural colors in your images. This filter is suitable for imagers on the outskirts of town, dealing with moderate levels of light pollution.
SkyTech CLS-CCD (Includes UV/IR Block) Filter
The CLS-CCD filter improves the visibility of deep sky objects while blocking out a great deal of city glow. This version is suitable for modified DSLRs because of the built-in UV/IR block filter. This produces smaller, sharper stars.
SkyTech LPRO Max (Landscape Astrophotography) Filter
This version has a finely tuned band-pass that blocks light pollution while allowing a very natural star colors to pass through. This results in a more natural-looking Milky Way, and the best option for wide angle nightscape shooters.
At the end of the day, you’re going to have to make the call on which astrophotography filter is best for your unique imaging situation.
These clip-in filters were graciously sent to me from Ontario Telescope and Accessories. If you live in North America, I highly recommend checking out their growing list of products to support backyard astrophotographers such as myself.
SkyTech CLS-CCD Astrophotography Filter Review [Video]
In the video below you will see actual results using the CLS-CCD filter using my DSLR and telescope. The imaging target is the Omega Nebula, which was shot on May 30th using data captured through the SkyTech filter.
Dealing with the City Glow
Many DSLR astrophotography enthusiasts live in areas away from large cities, or perhaps on an island where vast views over a large body of water are available. Others (like myself) are not so lucky. If we want to make this hobby work, we need to get creative.
I live in a medium-sized city in Southern Ontario. Light Pollution from Niagara Falls is to my East, and Toronto to the North. To make matters worse, I live almost directly in the center of town. This all contributes to a washed out night sky full of street lamp glow and more.
My Un-Filtered Backyard Sky:
Just have a look at the single exposure above without using a filter on my DSLR camera. Pretty scary, isn’t it?
Despite these shortcomings, I continue to execute deep-sky images through my telescope month after month. Filters, such as the SkyTech CLS-CCD Clip-in filter make this possible.
Don’t believe me? Using the filter on my DSLR allows me to capture exactly what I am missing up there.
The intense glow of the city can still be seen creeping into the Milky Way, but the light pollution filter has revealed the wondrous starry sky beneath the curtain of light. The photo above is a stacked composite of 11 images shot using the SkyTech CLS-CCD filter, and a wide angle camera lens.
Like many of you, I am very interested in anything that can help me partake in astrophotography from the comfort of my own backyard.
Even with the use of a light pollution filter, we must then bring the final stacked image into Photoshop for image processing. Adjusting the levels and setting the black point finally reveal the deep sky wonders in the photo, and obliterate the ugly glow of a washed out night sky.
Image Tests from the Backyard
My backyard is classified as a red-zone on the light pollution map, which is the second worst amount of LP possible. So, your images may look better or worse depending on the amount of light pollution you deal with.
These photos were captured using a Canon 7D Mark II DSLR with an EF 17-40mm f/4L USM Lens. The ISO was set to 6400, and each exposure was 30-seconds long. The cameras white balance was set to auto, as these RAW images will be adjusted in post processing.
As you can see, very few (if any) stars can be seen in the RAW image frames. However, the amount of overall light filtered is evident. As expected, the LPRO Max filter from SkyTech lets the widest array of light wavelengths through, to capture the true color of the landscape, while keeping light pollution at bay.
The LPRO max filter would be best used in a rural environment with a pleasing landscape, rather than a backyard in the city.
Deep sky with the CLS-CCD filter
In case you didn’t watch the video, here is the Omega Nebula I captured using the SkyTech CLS-CCD filter in my Canon 600D. The raw data actually looked better than what I was getting with my previous IDAS LPS filter in terms of contrast in the deep sky object.
The IDAS LPS Filter does edge out the SkyTech CLS-CCD in terms of natural sky and star color, but at the cost of less contrast. The LPRO Max and CLS filters offer a wider band-pass for more natural looking stars. I’ll discuss my way around this below.
M17: The Omega Nebula
Date: May 30, 2017
Total Exposure: 1 Hour, 18 Minutes
Frames: 26 x 180″ (RGB)
As you can see, an impressive amount of light from the deep sky object was able to be recorded through the light pollution. Also, the stars are small and sharp due to the UV/IR qualities of the SkyTech CLS-CCD filter.
The transmission graph above shows exactly where the CLS-CCD filter excels – Emission Nebulae from the city.
The Canon 600D was attached to my Explore Scientific ED102 Telescope with an Altair Lightwave 0.8 Field Flattener installed. The focal length of my ED 102 is perfect for capturing wide field views of the nebulae in Sagittarius. Related: Recommended Astrophotography Telescopes.
Producing a Natural Star Color
The star color and background sky are a little on the red side, so that will need to be corrected by shooting subs using a filter with a wider band-pass. There are a few options here, including shooting a number of image frames using the LPRO Max filter, or IDAS. These images can then be combined in Photoshop to create a composite with both the intense deep sky details and natural sky and star color.
The photo on the left is an old version of the Omega Nebula using the IDAS LPS filter. This shows how the star color is more natural, but less detail was captured in the nebula. See the composite version of both data sets.
For a breakdown of the steps used to process this image, have a look at my recent deep sky image processing tutorial.
Wide Angle using a Camera Lens
By now you should have an idea of how much light these filters let in, and how the CLS-CCD filter performs on deep sky objects. But what about a wide angle shot using a DSLR and camera lens attached to a tracking mount?
On May 30th I mounted my Canon 450D to an iOptron SkyGuider pro for a wide field look at the constellation Cygnus.
I’ll cover the amazing iOptron SkyGuider Pro in a future video and post (spoiler – I LOVE it). Below you can see the configuration used for the photos I am about to share.
The combination of a modified DSLR such as the 450D with a 50mm camera lens attached offers some tempting photography possibilities. The 50mm lens I use is lightweight and affordable. Best of all, it fits nicely over any clip-in astrophotography filter you choose to use on your DSLR.
At a fixed 50mm focal length, the Canon EF f/1.8 STM Lens fits multiple deep-sky objects in one shot. This is especially effective in capturing the nebulae in Milky Way with your modified DSLR.
Example using the SkyTech CLS Filter:
The photo above is a stack of 24 x 90-second exposures at ISO 800. The camera lens used was a Canon EF 50mm f/1.8 lens (Shot at f/2.8) This photo was captured through extremely heavy light pollution using the SkyTech CLS filter in the DSLR.
A 90-second exposure of this area of te sky without a filter would be completely white!
Finding The Milky Way through the Light Pollution
Here is the RAW image data collected using the SkyTech CLS-CCD filter on through a 50mm Camera Lens. These 90-Second exposures were then stacked in deep sky stacker with no darks, flats or bias frames.
Due to the extreme light pollution from my backyard, I’ve decided to create a greyscale version of my image. This way, you can see the detail acquired in the Milky Way without the nasty impurities in the background sky color.
Shots like this get me really excited. How many Deep sky objects in the Milky Way can you count? The Omega Nebula, Eagle Nebula, and Lagoon jump out at me, but there are many more in there. That is the magic of a light pollution filter.
Imagine what you could accomplish in moderately light polluted skies?
To cut through all of the city glow to reveal these objects in space is truly remarkable. No longer do amateur astrophotographers need to travel great distances to photograph space. It’s all available to you in your backyard, and this is proof.
The Bottom Line
If you are an amateur astrophotographer in the city, a light pollution filter such as the SkyTech CLS will open new doors to your DSLR astrophotography. Whether you shoot with a stock or modified camera, these Canon clip-in filters will block plenty of unwanted light.
Who are these filters suitable for?
Those of you who shoot Milky Way panoramics using a wide angle camera lens will benefit from the LPRO Max filter with its natural sky and star color qualities. I don’t recommend trying to create a wide-angle Milky Way portrait from your suburban backyard, save that for a camping trip or trip to darker skies.
While it is exciting to see the Milky Way from a city location, taming the overwhelming glow in post-processing can be a pain. For me, a 20-minute drive out of town with the iOptron SkyGuider pro would make more sense.
Which filter do you recommend most?
I have tested these filters both through a telescope and with a camera lens, and my results were impressive.
The SkyTech CLS-CCD is the best option for modified DSLR deep sky astrophotography.
If you shoot DSLR deep sky astrophotography with a modified Canon camera, the SkyTech CLS-CCD is a must. It performs as well (if not better) than my existing IDAS Light Pollution Suppression filter in terms of pure light pollution blocking power, and costs much less.
The California Nebula captured using a Canon 600D + SkyTech CLS-CCD filter through a Meade 70mm Quadruplet Apo
The LPRO Max is an interesting option for those who wish to create starry landscape images of the Milky Way. It lets enough natural light pass through to the sensor for natural colors, with the added benefit of reducing city glow.
The CLS filter is the most affordable option and is comparable to the Astronomik CLS. This version is an excellent option for astrophotography with a stock DSLR.
I hope you have found this resource useful in your on-going passion for capturing the night sky. For the latest information and tips, please follow AstroBackyard on Facebook.