Optolong Dual-Band L-eXtreme Filter

Optolong Dual-Band L-eXtreme Filter

  (30 Reviews)
✓ 2 year warranty


8x in stock shipped 1-2 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.

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

The advantage of the L-eXtreme filter is there is no transmission between the H-beta and OIII lines, as there are no nebula emission lines. So it doesn't let light pollution through, maximising nebulae signal and darkening the sky background.

The Optolong L-eXtreme filter better isolates emission lines and provides higher protection from light pollution.

IMPORTANT: Filters manufactured by Optolong are NOT designed for observing or photographing the Sun. DO NOT use Optolong filters to observe or photograph the Sun. If you do, it will result in permanent eye damage! 


  • 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 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 DSLRs (digital SLR) and monochrome CCD cameras; it is also more suited for fast systems. This filter's convenience and cost-effectiveness allow amateurs to image rich emission nebulas, even in bright, light pollution skies. Optolong believes the design of the L-eXtreme filter would be a better choice for fast systems at a competitive price. It isolates the H-Alpha, and Oxygen III nebula emission lines so that the contrast and signal-to-noise ratio between nebulae are maximised. For people 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 the visible substance in space. Our sun is 5 billion years old, but so far, hydrogen is still the critical matter of nuclear fusion. While the Sulfur element does not have much scientific significance, keeping H and O is meaningful for exploring 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 (30 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Great First Light
23 December 2022  | 

Bought this to upgrade from a broader Triband filter and managed to get 4 hours on the Tadpole nebula the day it arrived. I was very happy with the HOO image I was able to create.
Item arrived very quickly as is always the case for FLO.

Rating (max 5):  
Optolong L Extreme 1.25 inch filter.
09 December 2022  | 

I've enjoyed taking images using this filter over that last few days with the bright moon.
The 1.25 inch filter fits perfectly directly in front of the sensor on my ASI533 camera.
I've had some good images which have been a lot easier to process than with my previous filter L Enhance, they are much more defined with more detail.
The image really does stand out from the background and I don't get the halos around stars like other people have reported in various places.
The one negative thing is that when the moon was full yesterday, I have streaks of 0iii in places in my images. I will continue to monitor the performance of the filter and check if the streaks go away, they were not there before full moon.
I live in Bortle 5/6 area with industrial estate LED lights not far away and neighbours who have LED outside lighting.

Rating (max 5):  
Great filter
14 November 2022  | 

Expensive glass which will hopefully deliver over the years to come. Great reviews and images on the Web persuaded me to purchase this filter after doing my research. Great service from FLO and fast delivery.

Rating (max 5):  
04 November 2022  | 

Gamechanger. That is all

Rating (max 5):  
Great Product and service
09 July 2022  | 

Fantastic filter and as always a first class service from FLO

Rating (max 5):  
Optolong L-eXtreme Filter
28 January 2022  | 

For me, in terms of detail captured, this is an absolute game changer. I couldn't work out 'correct' exposure times and gain settings, so my first light with this filter was guess work. Even so, with just a few subs I could see more detail in the Elephant's Trunk Nebula than I had ever managed to capture before, even with hours of data. I have a lot to learn in regard to processing the data produced by this filter but already this feels like a massive leap forward on my AP journey.

Rating (max 5):  
18 November 2021  | 

This is just an amazing piece of filter. We are using it bortle 9 sky.

Rating (max 5):  
I don't even know what I'm doing, and this came out of Bortle 8 Dartford skies.
26 September 2021  | 


Rating (max 5):  
Optolong L-Extreme - well worth the money!
23 September 2021  | 

Finally got the chance to try this filter on a DSO. I had previously imaged the Eastern Veil Nebula with Skywatcher 200P and Canon 1000D (modded), proding a reasonable image with 1.5 hrs of data. However, the image was dominated by the star field and there wasn't very much blue nebulosity (OIII emission). The Optolong L-Extreme improved this enormously, isolating the HA and OIII nebulosity beautifully and enhancing the nebula above the background star field. All on 1.5 hours (5 minute subs) exposure, with a full moon nearby! Very pleased with this filter.

Rating (max 5):  
Stunning Results
16 September 2021  | 

I already had the ZWO duo-band filter, but seeing other images taken with this filter, I took a punt on it to see how much of a difference this filter makes. I was absolutely blown away by the immense richness of the colours, with limited clear skies of late, I only had one night but imaged both the east veil nebula (C33 - NGC 6992) and the bubble nebula (C11 NGC7635) and the results were stunning, so looking forward to the coming dark skies season and have a list of objects to capture.

I am using this with the ZWO filter wheel and the ASI 533MC Pro, with William Optics Z73 APO

Read all 30 customer reviews...


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