Astronomy Specialist


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Coming soon!


The new Optolong L-Ultimate filter is a light pollution dual band filter designed to drastically reduce the effect of light pollution. Its two ultra-narrow 3nm passing bands isolate the nebulae emissions in H-Alpha (red) and OIII (green-blue).

It blocks the light pollution, maximises nebulae signal and makes the sky background dark. The L-Ultimate filter is designed for astrophotography under urban skies.

  • 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 3nm.
  • Designed mainly for astrophotography.
  • Ideal for urban areas with extreme 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 3nm
Glass thickness

2.0 mm (for 1.25" and 2" filters)

Optical flatness

1/4 λ (wavefront)

Band-pass transmission TBD
Coating Fully multi-coated
Surface quality
60/40 (in accordance with US military watch MIL-O-13830)
Parallelism 30"
Glass type
Schott monolithic optical substrate (non glued)
Available sizes 1.25", 2"


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