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

Optolong Dual-Band L-eXtreme Filter

  (8 Reviews)
✓ 2 year warranty


Out of stock due 30-40 working days

About this product

Model:  opt_l-extreme_1.25
Part Number:  13801

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 (8 Reviews):  
Write a Review and share your opinions!

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.

Rating (max 5):  
Optolong L Extreme
Tuesday, 10 November 2020  | 

Amazing results with an ASI 533MC Pro. Highly recommended, particularly if you are in a Bortle zone 8-9 like me. Getting results that I never thought possible from my site.

Rating (max 5):  
Saved me time and money
Sunday, 4 October 2020  | 

I use this attached between a 72mm doublet and 533mc pro OSC. Before this filter, I had to drive an hour from a bortle 9 house location to a bortle 4 wilderness, spend 3 hours there scared at darkness, and drive back home for another hour tired and sleepy. This filter saved me from wasting 2 hours on road, spending on fuel and car running costs and most importantly horror of darkness at wild. I can have 10 minute subs under intense light pollution of Doha city including white LED street lights. So far I had great results on nebulas. I can barely see a max of 10 stars with my eyes and this filter can extract nebulosity in 10 min subs.

Rating (max 5):  
Extrememly fast delivery
Wednesday, 19 August 2020  | 

Received order after 2 days (int'l) - extremely fast!
Will review filter after use!

Rating (max 5):  
Awesome filter!!
Tuesday, 18 August 2020  | 

Highly recommended. The OIII and Ha signals are very strong with this filter. Extremely good for nebulae!

Rating (max 5):  
Optolong L-Extreme 2" mounted
Monday, 17 August 2020  | 

Thanks to FLO for very fast delivery!

Rating (max 5):  
eXtremely awesome filter!
Friday, 14 August 2020  | 

Optolong L-eXtreme dual narrow band filter is truly awesome! I live in city under bortle 9 skies and I can capture awesome nebula images using this filter with my color astrocamera! This imaging season will be awesome with this filter! Many thanks to FLO team for quick delivery!

Rating (max 5):  
The L-Extreme Rocks!
Tuesday, 11 August 2020  | 

I am happy with my purchase. Effective for fighting light pollution. Reduces star glow and enhances nebulas. Perfect match for my RASA8.


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