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Optolong L-Ultimate Dual Narrowband Filter Review from the City

Updated: Jun 4, 2023

Optolong is well known and respected for their high-quality astrophotography filters, for both planetary and deep sky imaging purposes.

In the Summer of 2022, Optolong released their newest deep sky astrophotography filter, a dual-band narrowband filter named "Optolong L-Ultimate". We never had the chance to try their previous narrowband filters (the L-eNhance and L-eXtreme), but with a name as cool as this, we had to try their newest one!

Scroll down to download example frames taken with this filter if you want to analyze it yourself!

Optolong L-Ultimate Narrowband Filter review

In this post, we will put this filter to the test from our extremely light-polluted Las Vegas backyard (Bortle 9, "white zone") with the moon almost full in the sky, and see how it performs! We'll also tell you if the L-Ultimate is worth the upgrade from the L-eNhance and L-eXtreme filters, and give you the key specs of this product.


What is the Optolong L-Ultimate?

The Optolong L-Ultimate filter is a narrowband filter for color cameras. It can be used with DSLR cameras, CMOS, and CCD cameras. Tonight, we will be using this filter with our One-Shot-Color QHY600C camera, and our 75mm refractor telescope.

Unlike the L-eNhance and L-eXtreme filters, which have a bandpass of 7nm, the L-Ultimate filter is a 3nm filter, giving it some advantages over the previous versions.

3nm filters are supposed to be much better at blocking unwanted light pollution, and also do a better job at shooting bright stars without halo artifacts. This is actually the reason we upgraded our monochrome narrowband filters, from 7 to 3nm filters. We now don’t have any more halos and can get much cleaner images from the city.

Sadr in OIII - 7nm vs 3nm filter
Sadr in OIII - 7nm vs 3nm filter

The L-Ultimate filter only allows the OIII (500.7nm) and HA (656.3nm) emission lines through. All other light pollution emission lines are blocked by the filter, including artificial light from mercury vapor lamps, sodium vapor lights, and other emissions from the neutral oxygen in the atmosphere.

Here you can see the full specifications taken from Optolong’s website:

  • Substrate: Optical Glass

  • Size: 2" mounted (M48x0.75 thread)

  • Thickness: 1.85mm

  • FWHM: OIII 3nm, Ha 3nm

  • Blocking Range: 300-1000nm

  • Blocking: OD4

  • Surface quality: 60/40

  • Transmitted Wavefront RMS: λ/4

  • Parallelism: 30seconds

Be aware that the Optolong L-Ultimate is not a great fit for fast telescopes. A focal ratio of f/4 might be okay, but faster optics like the RASA (f/2) will need a wider bandpass, like the L-eXtreme for example.

Note: Some users reported that the L-eXtreme paired with the RASA caused band shift, thus clipping the HA data. The Triad Ultra might be to this day the best fit for such fast telescopes.

The Optolong L-Ultimate filter, just like most filters for color cameras, is a mounted filter so it is easy to thread it onto a telescope.

We’ve been thinking of the best possible way to review this filter, and we’ve come up with a masterplan, which is to have 3 different types of data to analyze:

  • We’ll dedicate 15 hours on a nebula and image it to the best of our abilities so that we can see what the filter can achieve on a serious imaging run.

  • We’ll image a second nebula but this time without spending too much time on it, to see how the filter performs on a "quick night".

  • We’ll take some quick single shots of random targets and stars and see if we get weird artifacts or halos.

So let’s get to work for the next several nights, and then analyze all the data we got! Be sure to watch our full video to hear our thoughts as we open and zoom in on each image for the first time.


Optolong L-Ultimate Astrophotography - 15 Hours on the Wizard Nebula

Our first experiment will be to image a nebula for a couple of nights, and see how the L-Ultimate filter performs on a target that has plenty of signal-to-noise ratio. As a reminder, all the images you see on this post were taken from our Bortle 9 city backyard. The moon was also high in the sky and almost full, so there was plenty of light pollution!

This data, despite being noisy, was full of details and colors! The stars look great, and only the right bright star near the edge of the frame is affected by a halo, and it is very minimal! Overall, we are very pleased with the results obtained on this target using the filter.

Click the image to see it in higher resolution

Wizard Nebula with the Optolong L-Ultimate filter

Want to process your images following our own workflow? Download our PixInsight PDF Guide!

Camera: QHY600C

Telescope: Radian 75

Mount: ZWO AM5

Processing: Pixinsight


Total Exposure Time: 15 hours

Exposure Time per frame: 10 minutes

Gain: 26


Optolong L-Ultimate Astrophotography - 2.5 Hours on the Omega Nebula

Our second test will be a short session on the Omega Nebula. M17 is located in the Milky Way band and is fairly bright, it is also surrounded by a lot of hydrogen alpha gas.

Once again here, the stars look nice, and the data is full of colors and details even with less than 3 hours of total integration time! You can see the bright gases within the Omega Nebula, but also the fainter gases visible all around the frame.

Click the image to see it in higher resolution

Omega Nebula with the L-Ultimate filter

Camera: QHY600C

Telescope: Radian 75

Mount: ZWO AM5

Processing: Pixinsight


Total Exposure Time: 2.5 hours

Exposure Time per frame: 10 minutes

Gain: 26


Optolong L-eNhance vs L-eXtreme vs L-Ultimate

If you already own the L-eNhance or the L-eXtreme filter from Optolong, is the L-Ultimate worth the upgrade?

Like we said earlier, we sadly never had the chance to use these two previous filters, so we cannot show some comparison shots, but we can see some key differences between the three by looking at the specifications.

Optolong states that the L-Ultimate filter is better at letting ONLY Ha and OIII emission lines through, gives a darker sky background, more contrast, and nicer stars. The L-Ultimate filter is also supposed to do a better job at halos and almost completely eliminate them depending on the star visible in the frame, thanks to the 3nm bandpass.

In short, the L-Ultimate will block more unwanted light compared to the previous filters. Your image will have more contrast, a darker sky, and nicer stars. If you already own the L-eNhance or the L-eXtreme, spending another $389 might not be worth it unless you are really bothered with the halos you are currently getting.


Optolong L-Ultimate Filter - Random Test Shots

Lastly, we decided to take a few random test shots of a few objects, just so we could zoom in on the image and see if we could see any strange artifacts, halos, or gradients.

L-Ultimate filter test shots

You might want to watch the review video if you'd like to see these images as we zoom in on each of them in 4K screen recording. We took single 10 minutes shots of the Wizard Nebula, the Omega Nebula, the Sadr Region, the Veil Nebula, and the Question Mark Nebula.

We were very surprised to see no halo at all on the bright star Sadr, which definitely has halos on 7nm filters. This proves that the 3nm bandpass really helps with getting much cleaner bright stars.

Downloadable Raw Data

Want to analyze the data yourself? You can download 3 example raw frames below!

L-Ultimate Raw Frames
Download ZIP • 217.45MB


Final Thoughts

We are very impressed with the Optolong L-Ultimate filter! We will likely use this filter often when imaging with a color camera from home

Be sure to watch our review video, and let us know what you think of this filter if you own it!

Make sure to follow us on Facebook, Instagram, and YouTube to stay up to date with our work!

Clear Skies,

Galactic Hunter

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