Optolong L-eXtreme F2 High Speed Narrow Band Filter

Optolong L-eXtreme F2 High Speed Narrow Band Filter

£298.00✓ 2 year warranty


5x in stock shipped 1-2 working days

About this product

Model:  opt_l-extreme_F2
Part Number:  L-eXtreme F2

NEW Optolong L-eXtreme F2 High-Speed Narrow Band Filter.

Optolong has developed this new filter for fast optical systems, or fast focal ratio imaging systems. It performs well when used with RASA, HyperStar and other fast focal ratio telescopes. 

The Optolong L-eXtreme F2 is a dual-band (500.7 nm and 656.28 nm, FWHM=7 nm) 2" narrowband pass filter that meets the requirements for transmission at continuously varying angles.

Astronomically characterised spectral lines (OIII, Ha) as the main transmission wavelengths, the OIII and H-Alpha nebula emission lines pass accurately at f2 - f3.3 Focal Ratio. 

Key Features:

  • Ideal for use with one-shot colour and mono astronomical cameras, and Digital SLR cameras - quickly obtain clear and detailed images of the deep sky.
  • Works well with fast optical systems such as RASA, Hyperstar and other fast focal ratio telescopes.
  • Recommended for focal ratios from f2 to f3.3.
  • Reduces light pollution for higher contrasting detail.
  • Cuts background light and noise beyond the target celestial bodies to further enhance detail and contrast.

Currently available as a 2" Filter only. 

Based on the characteristics of emission nebulae and light pollution emission lines, the L-eXtreme F2 retains the prominent OIII and Ha wavelengths while blocking most light pollution. Specifically designed and optimally calculated for the characteristics of a fast optical system, the L-eXtreme F2 maintains high OIII and Ha transmittance.

The horizontal axis is the Wavelength in Nanometers(nm).

The vertical axis is transmission in %.

Coating Technology

  • Multi-layer anti-reflection coating. 
  • Non-cementing optical substrate coating. 
  • Optolong filter adopts precision coating based on Ion-assisted deposition coating technology for durability (resists scratching) and stability on CWL (central wavelength) with no deviation from temperature change.
  • A planetary rotation system ensures precision and homogeneity of optical coatings, high value on the transmission of pass-band, and Optical density of off-band.



Substrate Optical glass
Thickness 1.85mm

OIII 7nm

Ha 7nm

Blocking range 300-1000nm
Blocking Depth >OD4
Surface quality 60/40
Transmitted Wavefront RMS λ/4
 Parallelism 30s


Customer reviews

Be the first to Write a Review for this item!


Please fill in the form below to ask a question.

Please add the two numbers