Optolong L-eXtreme Filter Review by AstroBackyard
Optolong L-eXtreme Filter Review
August 13, 2020|Nebulae|21 Comments
The Optolong L-eXtreme filter is now being used in backyards across the globe, which is great news for those that take astrophotography images in heavy light pollution.
This astrophotography filter features even narrower bandpasses than last year’s L-eNhance, making it perfect for nebula photography from the city.
The Optolong L-eXtreme filter isolates the H-alpha (Ha), and Oxygen III (OIII) at 7nm exclusively. Unlike the previous L-eNhance, the eXtreme does not include a bandpass for H-Beta (Hb).
The more selective bandpass transmissions are more suitable for fast optical systems, such as an F/2 RASA or Starizona Hyperstar configuration.
In this article, I will share my results using the Optolong L-eXtreme filter with 2 different color astrophotography cameras.
I have tested the Optolong L-eXtreme filter using a one-shot-color dedicated astronomy camera (QHY268C), and a Mirrorless Canon EOS Ra. The telescopes were both apochromatic refractors with f-ratios of F/5.5, and F/7.
If you have tested the performance of this filter using a contrasting optical instrument (such as a camera lens or larger Schmidt-Cassegrain Telescope), please share your experiences in the comments!
The Eastern Veil Nebula captured using the Optolong L-eXtreme Filter. (Click for larger version)
From the moment I first heard the announcement of the Optolong L-eXtreme filter on Twitter, I was intrigued. The Optolong L-eNhance filter has been one of my favorite and most well-used filters to date, and the L-eXtreme promised to be even more effective at ignoring light pollution.
The L-eNhance was a popular choice for many backyard astrophotographers looking for an affordable solution for their color cameras, and I was not surprised to see the buzz around the improved L-eXtreme version.
The most obvious difference between the L-eXtreme and L-eNhance filters are the transmission lines. The L-eNhance allows a 24nm bandpass through the OIII and H-Beta region, and 10nm for Ha. The L-eXtreme, on the other hand, is strictly 7nm in Ha and OIII.
The official language from Optolong about what makes this filter so special:
“the advantage of the L-eXtreme filter is that there is no transmission between the H-beta and OIII lines and there are also no nebula emission lines there. In this case, it isn’t letting light pollution come through so it maximizes nebula signals and the sky background is made darker while imaging.”--- from Starizona.
I shoot 95% of my astrophotography images from my Bortle Scale Class 7 backyard in the city, and light pollution filters are necessary to capture my images. Broadband targets such as galaxies are tough, which is why I usually reserve those objects for dark sky excursions.
Nebulae, on the other hand, are much more obtainable from a light-polluted city. The L-eXtreme excels at capturing high-contrast images with a greater separation between the nebula wavelengths and a light-polluted sky.
FWHM: O3 7nm+Ha 7nm
Blocking range: 300-1000nm
Blocking depth: light pollution line blocking >99%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
The transmission graph of the Optolong L-eXtreme Filter (Optolong).
As you can see, the bandpass allowance for this filter is extremely (pardon the pun) selective. This is fantastic if you enjoy high-contrast images of bright emission nebulae, but less useful if your imaging projects include broadband galaxies or reflection nebulae.
Compared to the transmission graph of the Optolong L-eNhance filter, the eXtreme blocks the Hb and region between Hb and OIII. It’s a tighter bandpass allowance in OIII and Ha overall (7nm for each).
In my personal experience, some of the most fun projects are built using multiple filters. To capture incredible astrophotography images from a light-polluted location (my backyard is a Bortle Scale class 7), you need to get a little creative.
I have slotted a 2″ Optolong L-eXtreme filter into the camera adapter of my Sky-Watcher Esprit 100 rig. The filter sits in front of the QHY268C color camera, and the 550mm focal length Sky-Watcher Esprit 100 APO.
A filter drawer is a better solution, especially for projects that involve capturing images over long periods of time through various filters. No more threading the filters in ad out and changing the rotation of your imaging train.
I originally began photographing the Veil Nebula using the Starizona 0.65 reducer/flattener on my Sky-Watcher Esprit 100, but spacing issues led me back to the native focal length of 550mm. Even without the reducer, the APS-C (crop-sensor) of the QHY268C provides an impressive field of view through the Esprit 100.
The QHY268C is an ideal candidate for the Optolong L-eXtreme filter. This cooled, one-shot-color camera collects images full-color images at once, and colorful emission nebulae can be recorded using only one filter.
Yes, building an image with a monochrome camera using LRGB and dedicated narrowband filters may yield a higher-quality result, but this process is not always convenient or accessible to many imagers.
I’ve also tested the Optolong L-eXtreme filter with my Canon EOS Ra mirrorless camera. In this imaging configuration, I simply threaded the 2″ filter inside of the adapter that attaches to the focuser of my telescope.
The location of the 2″ filter in your imaging train will vary depending on the equipment you use. I find 2″ round-mounted filters to be the best overall choice in terms of format, no matter which camera you use.
Who Needs This Filter?
If you enjoy photographing nebulae with a color camera, the Optolong L-eXtreme is an exciting option. One of the most challenging aspects of deep-sky astrophotography early on is dealing with large, blown-out stars, and horrible gradients in the sky.
A narrowband filter (or this case, dual-narrowband) corrects these issues to a large extent by isolating the important wavelengths of light we want to collect on the sensor.
With these impressive narrowband capabilities comes some additional challenges for amateur astrophotography enthusiasts. For example, if you are accustomed to using a DSLR camera and a simple broadband light pollution filter (such as the Optolong L-Pro), you may find the process of focusing your camera and telescope much more difficult using this filter.
The narrow bandpass emission lines mean that much less light is reaching the camera sensor overall, meaning framing and focusing your target can be challenging. If you are using the live-view focusing method on your DSLR camera, don’t be surprised if only the brightest stars are visible.
A one-shot-color astronomy camera like the QHY268C is a great match for this filter.
With that being said, those using older DLSR models such as a Canon Rebel series body older than the EOS T3i may find it very difficult to frame and focus your targets.
Modern DSLR’s and mirrorless cameras (such as the Canon EOS Ra) have higher ISO settings and improved LCD display screens that make using the “live-view” function of the camera easier.
Image Test Results
Testing a camera filter requires clear conditions and time. I managed to “complete” 3-4 impressive images, with relatively short integration times.
Since the Optolong L-eXtreme filter specializes in isolating the Ha and OIII wavelengths of gas in an object, I chose to photograph a bright emission nebula target that emits a strong signal in both bands. The Lagoon Nebula contains plenty of h-alpha and oxygen III details:
Here is the version of the image I shared on Instagram.
The Lagoon Nebula. Canon EOS Ra and Optolong L-eXtreme Filter.
Integration: 21 x 5-minutes at ISO 3200 (1.75 hours)
Calibration: 15 Dark Frames, 15 Flat Frames
Processing: Adobe Photoshop 2020
Camera: Canon EOS Ra
Telescope: Sky-Watcher Esprit 150
Mount: Sky-Watcher EQ8-R Pro
As you can see in the image, the intense regions of hydrogen and oxygen are well separated from a light-polluted sky. I find this particular deep-sky object to be one of the best overall test subjects for a dual bandpass filter.
It’s worth noting that all dual bandpass/tri-band filters seem to create a pleasing result on this subject. A better performance indicator for the Optolong L-eXtreme is to shoot something less bright, in the direction of the light dome.
For my next test, I chose to photograph the Western Veil Nebula in Cygnus. This supernova remnant is very large and includes many interesting areas of nebulosity around the “witch’s broom” element (Cygnus Loop).
The prominent gases in this nebula jump off of the screen, as the filter is only allowing the light from the Veil Nebula complex to pass through to the sensor.
The Veil Nebula in Cygnus.
Integration: 23 x 4-minutes at Gain 100 (1.4 hours)
Calibration: 15 Dark Frames, 15 Flat Frames
Processing: Adobe Photoshop 2020
Telescope: Sky-Watcher Esprit 100
Mount: Sky-Watcher EQ6-R Pro
In both cases, the stars in the image are recorded rather colorless. This is one of the main drawbacks of a dual-bandpass narrowband filter. For accurate star colors, a broadband filter must be used.
It is possible to correct the star colors synthetically (to a degree), but this can be a painstaking process and difficult to accomplish effectively. I recommend re-shooting the target with a broad-spectrum filter such as the Optolong L-Pro.
The Optolong L-eXtreme filter keeps stars exceptionally small, which creates a pleasing effect on most nebulae targets. For those struggling with bloated, fat stars in their images, a dual-bandpass narrowband filter like this may be a great solution for you.
Below, is an up-close look at a section of the Veil Nebula image that shows just how subdued the stars are with this filter. No star minimizing actions have been applied to this data.
The dramatic separation between the nebula and a light-polluted sky.
Have a look at the individual color channels of my RGB image. Here, you’ll notice a strong signal in each channel, recorded in a single exposure.
For anyone looking to maximize their limited time under a clear night sky, I think you’ll find it hard to top the L-eXtreme / One-shot-color astronomy camera combination.
If you would like to take a closer look at data captured using the Optolong L-eXtreme filter, feel free to download my stacked image of the Veil Nebula.
The RGB channels of my image using the L-eXtreme filter.
The Stacked Image
The following image displays the output from my short integration on the Lagoon Nebula in DeepSkyStacker. This image includes 21 light frames (5-minutes each), and 10 dark frames.
I was thrilled with the preview image shown on my computer screen, as this often indicates some impressive details are in the image, and will just need to be teased out further in Photoshop.
The stacked, linear image in DeepSkyStacker.
I share this because I don’t often see such an impressive looking image ‘out of the box’. Normally, a lot of stretching and separation between the deep-sky object and the sky must take place in Photoshop to achieve this look.
The Optolong L-eXtreme filter creates a truly remarkable image exposure out of the camera, and 5 years ago I would not have believed it were possible. The object is well defined against the sky, and balancing the colors in post is a straight-forward process.
For a better idea of what the linear image looks like before stretching occurs, have a look at the before-and-after of my Veil Nebula image.
It is very normal to start out with a green image when using a color CMOS camera with an RGB Bayer filter. But once the colors are balanced out, a beautiful deep-sky image is revealed.
You’ve seen the images, and you now know what you can expect with a one-shot-color camera. It’s designed for contrasty nebula photography, and it’s in a completely different class than a broadband filter like the L-Pro.
The Optolong L-eXtreme is still very new, but amateur astrophotographers have already had incredible success using this filter and have shared their results.
L-eXtreme vs. L-eNhance
If you were planning on purchasing the L-eNhance filter, and now have the opportunity to buy the L-eXtreme, I would spring for the L-eXtreme.
I believe that the Optolong L-eXtreme filter is an improvement over the L-eNhance. The added bandpass allowance of the L-eNhance did not add any extra meaningful signal in my experience.
The 24nm bandpass in the OIII and Hb region has been reduced to 7nm in OIII only, and I think this is a better fit for most users.
I’ve heard others mention that the blue channel, in particular, looks much cleaner in one-shot-color data with the L-eXtreme.
They are both fantastic filters for one-shot-color astrophotography in the city, but the L-eXtreme does a slightly better job at creating an impressive contrast between the Ha and OIII wavelengths and a light-polluted sky.
Compared to some of the other filters on the market, the Optolong L-eXtreme filter is quite affordable, too. I think anyone that invests in this light pollution filter will get plenty of use out of it for years to come.
I’ll continue to use the L-eXtreme in my backyard, as it will replace my L-eNhance in situations where this filter is well utilized. The only other filter I would consider as useful as the L-eXtreme is the Radian Triad Ultra, but I realize that this filter is much more expensive.
At the time of writing, this filter only comes in the 2″ round mounted option, and I don’t expect to see clip-in DSLR/mirrorless versions in the future.
The following image of the Eastern Veil Nebula captured by John Michael Bellisario is a testament to the quality of this filter.
The Eastern Veil Nebula shared on Instagram. John Michael Bellisario.
“The L-eXtreme is a huge jump in OSC narrowband technology. A lot of community feedback from the L-eNhance was addressed in the development of this filter.
This improvement was apparent in my first time processing L-eXtreme data. Many of the struggles with noise, gradients, and the blue channel which were common with the L-eNhance were no longer an issue.
The data it produces is very forgiving making it perfect for both advanced and beginning astrophotographers. In addition to producing excellent images right out of the stack, the 7nm bandpass allows you to image under heavy light pollution.”
Be sure to check out his Instagram account to see some more fantastic examples using this filter.
Dynamic separation between nebulae and the sky
Largely ignores city light pollution all together
Captures full-color images in a single exposure
Can be used during a full moon
Improved performance over the Optolong L-eNhance
More expensive than the L-eNhance filter
Star colors are not recorded accurately
Not suitable for broadband subjects (galaxies, reflection nebulae, etc.)
May be difficult to frame/focus targets with a DSLR camera
Not available in clip-in DSLR/Mirrorless format (currently)
The Helix Nebula. Optolong L-eXtreme filter + QHY268C.
I asked my good friend Ruzeen Farsad (AstroFarsography on YouTube) if he would be willing to share some thoughts on the Optolong L-eXtreme filter, as I know he has been using one for a few months now.
He graciously accepted, and had the following to say about this filter:
“When I heard about the L-eXtreme my ears perked up. Having had used the L-eNhance alongside the ASI 533mc Pro and having had amazing results, I was keen to see what this filter was capable of. I received one to review and then set to work.
The first night of testing I decided I needed to go for the low hanging fruit. Being summertime, it’s all about Cygnus and the veil nebulae. I was using my Sky-Watcher Evostar 80ED and a modified Canon 600D.
The first images were a bit of a let down though. I was expecting a learning curve using this filter.
The Eastern Veil Nebula by Ruzeen Farsad. Canon 600D (modified) and L-eXtreme
Shawn Neilson (Visibledark Astro on YouTube), shared this video on his channel about the Optolong L-eXtreme filter. Shawn has found a way to separate the color channels of the images shot using the Optolong L-eXtreme filter to create images that resemble the Hubble Palette.
The effect is truly remarkable, and I am actually quite blown away with his results using the QHY268C color camera.
Optolong L-eNhance vs. L-eXtreme (Forum Discussion)
10 Light Pollution Filter for Astrophotography in the City
Sky-Watcher Esprit 100 apochromatic refractor review
Optolong L-eNhance Filter Review
Deep-Sky Astrophotography Image Processing Guide
Important note: This is artical was abstracted from AstroBackyard web, click below image to see the full review. Thanks.