Astronomy Specialist


$499.00 AUD
SKU: OP-14803




The Optolong L-eXtreme f/2 filter is a light pollution dual band filter designed to drastically reduce the effect of light pollution with fast telescopes. The f/2 version has been specifically designed to work with telescopes which have a focal ratio between f/2 and f/3.3, such as Sharpstar's HNT hyperbolic astrographs and the Celestron RASA series.

Available in 2" mounted.



The advantage of the L-eXtreme filter is that there is no transmission between the H-Alpha and OIII lines as there are no nebula emission lines there. It blocks the light pollution, maximises nebulae signal and makes the sky background dark. The L-eXtreme filter works well under bright urban skies. Different from the Optolong L-eNhance filter which is a tri-band (transmits H-beta, H-Alpha, and OIII), the L-eXtreme filter is dual band to reduce the effect of light pollution even more.

This filter is designed for colour cameras used under urban skies. It works as a combined H-Alpha and OIII narrowband filter so photos will appear highly contrasted without the necessity to use a monochrome camera and two separate filters.

  • It blocks the artificial light from mercury vapour lamps, both high and low pressure sodium vapour lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).
  • Maximum transmission of the main nebula emission lines at OIII (496nm and 500nm) and H-alpha (656nm).
  • Two transmission bands with a bandpass of 7nm.
  • Ideal for fast optical systems such as the Takahashi Epsilon, Celestron RASA, Hyperstar and similar systems.
  • Ideal for urban areas with very high light pollution.
  • It incorporates an IR/UV-Cut filter that is necessary in astrophotography, especially for astronomy cameras that are sensitive to the infrared radiation.
  • Ultra-thin filter cell to maximise the compatibility with most filter wheels.
  • Multi-layers anti-reflection coating.
  • Cell in Aerometal Material, CNC machined, sand blasted, black anodized and laser engraved.
  • Plastic PP Case, high pressure EVA Case Lining.

Light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness. It does increase the contrast between nebulae and night sky.

The interferential coating is deposited on the substrate using electron-beam gun evaporation with Ion-assisted deposition coating technology. This increases the filter durability and resistance to scratching, as well as stability on CWL (central wavelength) and no deviation affected by temperature changes. The planetary rotation system offers precision and homogeneity of coatings ensuring high transmission of pass-band and high optical density off-band.

WARNING: Optolong filters are not designed for sun observations. DO NOT LOOK AT THE SUN WITH OPTOLONG FILTERS. You could become BLIND if you fail to observe the warning.

Passing band Dual band H-Alpha and OIII, 7 nm
Glass thickness

1.85 mm (for 2" filters)

Optical flatness

1/4 λ (wavefront)

Coating Fully multi-coated
Surface quality 60/40 (in accordance with US military watch MIL-O-13830)
Glass type Monolithic optical substrate (non glued)
Available sizes
SKU OP-14803 (2")



Belly of the Cygnus by Tommaso Massimo Stella | Optolong L-eXtreme f/2


Belly of the Cygnus by Tommaso Massimo Stella | Optolong L-eXtreme f/2 with 135mm f/2 lens.


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$499.00 AUD


  • 2"

Optical design

Image circle

Focal ratio


Focal length

Optical thickness



Colour or Mono

Pixel size

Sensor dimensions


Sensor diagonal

Quantum efficiency

Read noise

Fullwell capacity

Bit depth


Camera backfocus

Filter size

Filter size

Bandpass (FWHM)

Bandpass (FWHM)

Glass thickness

Mount type

Payload capacity

Latitude range

Dovetail saddle

Slew speed


Periodic error correction

Counterweight shaft

Azimuth adjustment range

Internal diameter

Illuminated diameter

Compatible telescope external diameter





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