Optolong Dual-Band L-eXtreme Filter
 Optolong Dual-Band L-eXtreme FilterOptolong Dual-Band L-eXtreme Filter 

Optolong Dual-Band L-eXtreme Filter

  (17 Reviews)
✓ 2 year warranty


34x in stock shipped 1-2 working days

About this product

Model:  opt_l-extreme_2
Part Number:  13802

New L-eXtreme Filters - Dual H-alpha / Oxygen III 7nm Narrowband Filter

For One Shot Colour / DSLR Imaging - Simultaneously Capture H-alpha and Oxygen III

The advantage of the L-eXtreme filter is that there is no transmission between the H-beta and OIII lines, as there is no nebula emission lines there. In this case, it isn't letting light pollution come through so that maximises nebulae signal and make the sky background darker while imaging. The L-eXtreme filter should better isolate the emission lines only and better protect from light pollution.

Unlike the Optolong L-eNhance filter which is a tri-band (transmits Hb, Ha, and OIII), the L-eXtreme filter is dual band that passes Ha and OIII emission lines.


  • High transmission of H-Alpha and Oxygen III emission lines (avg. 90% or higher)
  • FWHM: Ha 7nm, OIII 7nm
  • Use with colour DSLR, CMOS and CCD Cameras
  • 1.25" or 2" Mounted Filters.
  • Supplied in a protective plastic case with EVA foam lining
  • B270 1.85mm Thick Glass
  • Fine-optically polished on both sides - ensures accurate λ/4 wavefront and <30 seconds parallelism over the both surfaces
  • Ultrasonic wave cleaned substrate with purified water - Cleanup by 13 stage purified water tank to remove impurities and dust effectively
  • Ion source assisted coating— For durability and resistance to scratching, as well as stability on CWL (central wavelength)  - no deviation affected by temperature change
  • Stringent quality testing process - each filter is tested on a spectrophotometer and laser interferometer


L-eXtreme is a two 7nm bandpass filter which can be used with one-shot colour cameras like DSLR's (digital SLR), and monochrome CCD cameras, it is also more suited for fast systems. The convenience and cost effectiveness of this filter allows amateurs to image a rich emission nebulas, even in bright, light pollution skies. Optolong believes the design of L-eXtreme filter would be better choice for fast systems in competitive price. It isolates the H-Alpha, and Oxygen III nebula emission lines so that the contrast and signal-to-noise ratio between nebulae were maximised. For people who is living in very light polluted areas, or when the moon is out, the L-eXtreme will be a good filter.

Hydrogen is the largest, the most primitive, the simplest, and the oldest element in the universe. Scientists consider that Hydrogen amounts to more than 90% of visible substance in space. Our sun is 5 billion years old, but so far hydrogen is still the key matter of nuclear fusion. While the Sulfur element does not have much scientific significance, so keeping H and O is meaning for exploration of life.

Transmission Chart

White Line - Represents the transmission curve of the L-eXtreme Filter.

The Major Emission Lines of Nebulae: H-α (656.3nm), H-β (486.1nm), OIII (495.9nm) and OIII (500.7nm)

The Major Emission Lines of Artificial Light Pollution: Hg / Mercury (435.8nm, 546.1nm, 577nm and 578.1nm), Na / Sodium (598nm, 589.6nm, 615.4nm and 616.1nm)

Sample Images

  • Object: M42
  • Time : 15th.--16th. March 2020
  • Place: HongKong-Shatin
  • Camera : ZWO ASI183MC Pro
  • Telescope : f/5 @ Sky-Watcher N130/650 w coma corrector
  • Filter : Optolong  L-eXtreme 2"
  • Mount : iOptron CEM25EC
  • Guide : 120mm mini guide scope, ZWO ASI120MM mini
  • Light pollution level 7~8(City center, light pollution disaster area)
  • Copyright: ©Vincent Cheng (Hong Kong)


  • Object:NGC6946, Barnard 150 & Sh2-129 Flying Bat nebula
  • Equipment:Canon 6D mod+WO SpaceCat 51+Optolong L-eXtreme&L-Pro
  • Data:RGB 25 x 600" ISO 3200 - Optolong L-Pro
  • H-Alpha & OIII 20 x 1500" ISO 320 0 - Optolong L-eXtreme
  • Copyright: ©José Jiménez (Spain)

What's in the box

  • L-eXtreme Filter
  • Silver Cardboard Box
  • Plastic PP Box
  • High Pressure EVA case lining







O3 7nm+Ha 7nm

Blocking range


Blocking depth

Light pollution  lines blocked >99.9%

Surface quality


Transmitted Wavefront RMS




Customer reviews

Average Rating (17 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Incredible Contrast
Thursday, 22 July 2021  | 

I live in a Bortle 4/5 zone, with more light pollution towards the North, so wasnít sure how much of a difference this would make for the summer nebulae (was primarily bought for the northern DSOs such as heart / soul menís etc). However it is a game changer for everything. The signal and contrast from veil, butterfly, pelican nebulae were a step change improvement to equivalent images taken without it. Thoroughly recommend the L-extreme if you are after imaging the Ha O3 nebulae. Canít wait to have a look at Orion Ö.. Service from FLO was as excellent as ever.

Rating (max 5):  
Great Filter
Friday, 21 May 2021  | 

Only managed to use the filter for one short session (2hours) and was blown away with Subs and final image. I live in Bortle class 5 and the moon was at approx 50%, all subs came out clear with lost of nebula details. Final image show no star bloating and lots of detail for so little data. Highly recommend the filter and FLO as they have been great with every purchase I have made.

Rating (max 5):  
Tuesday, 27 April 2021  | 

Not used it yet but have read great reviews on it,
Great service from FLO as usual

Rating (max 5):  
A worthy addition to my filter set
Wednesday, 17 March 2021  | 

A fantastic filter. I had to wait a while to use it as the weather has been hindering progress. First light was on the Veil Nebula complex with a modified DSLR and Redcat 51. The first 5 minute exposure blew me away. The amount of Ha and OIII detail visible in a single image is astonishing. I had read that the filter was prone to creating haloís around brighter stars but Iíve yet to see any haloís in my images. I look forward to using this filter more and more as the quality it delivers speaks for itself.

Rating (max 5):  
Extremely Good
Tuesday, 2 March 2021  | 

Unlike most astro purchases this one arrived without clouds, 3 consecutive clear nights and a big bright moon. I inserted it between my astromodded DSLR and scope, I managed to get 5 hours of data over the first two nights of the Rosette Nebula and the quality of the subs was superb, processing the data was so easy, the result was probably the best astro picture I've ever produced. The 3rd night I tried to capture some data on IC 443 the Jellyfish Nebula, 3 hours just isn't enough on this target but what I have got looks very good, I shall be getting more data the next clear night, hopefully with less moon about.

Rating (max 5):  
Optolong L-Extreme filter
Tuesday, 2 March 2021  | 

Thanks to FLO for a very fast delivery. I tried out the filter with a ZS61 at F4.8 on the February 26th full moon night on several emission nebulae and obtained good results using exposures of 4 to 8 minutes, depending upon altitude, at ISO 800. The filter worked really well.

Rating (max 5):  
L Extreme 2Ē
Friday, 19 February 2021  | 

Amazing product. Really works in heavily light polluted skies. Highly recommended and lightning quick service as ever from FLO.

Rating (max 5):  
Does just as you would expect
Tuesday, 16 February 2021  | 

Only had a chance to use it once so far but the minute I slotted it in to my scope and looked at my real time image on my PC I could see a huge difference and the couple of objects that I did manage to shoot had far more detail and brightness.
I live in an area where there are LED Street lamps and the Optolong L-Extreme seems to just cut straight past them.

Highly recommended for anyone wanting to get great images of emission nebula, supernova remnants and the like with a OSC or DSLR.

Rating (max 5):  
Tuesday, 16 February 2021  | 

Only had chance to use once so far due to clouds, but am amazed at the results, looking forward to using again

Rating (max 5):  
Worth the wait
Tuesday, 1 December 2020  | 

Due to the disruption caused by Covid, I had to wait a while before this 2" L-eXtreme filter arrived, and I've had it for a short while now but long enough to be impressed. I've reserved it for shooting while the moon is fairly well illuminated, and even shooting fairly close to the moon I get decent results. It really does manage to darken the background and help bring out faint details. Well worth the money and the wait.

Read all 17 customer reviews...


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