Optolong 2" L-Extreme 7nm Dual Band Filter

The Optolong L-eXtreme is a dual 7nm bandpass filter which can be used with DSLR's (digital SLR), Once Shot Colour CMOS Cameras, and monochrome cameras. The convenience and cost effectiveness of this filter allows amateurs to image rich emission nebulas, even in bright, light polluted skies.

The L-Extreme isolates the H-Alpha, and Oxygen III nebula emission lines so that the contrast and signal-to-noise ratio between nebulae are maximized. For people who are living in very light polluted areas, or when the moon is out, the L-eXtreme is an excellent choice

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.The advantage of the L-eXtreme filter is that there is no transmission between the H-beta and OIII lines, where there are no nebula emission lines. In this case, the filter does not allow light pollution to pass that might be in this range, thereby maximising the nebulas signal and making the sky background darker.

Astrograph recommend this filter mainly for use with one shot colour (OSC) cameras. Although the filter passes only OIII and H-Alpha, OIII actually bridges the wavelengths accepted by both the Green and Blue filtered photosites of a colour camera. Red is obviously covered by the H-Alpha bandpass. All other wavelengths are effectively blocked allowing far higher signal to noise than traditional light pollution filters. The 7nm bandpass also means that contrast of nebula is increased compared to wider band 'tri-band' filters.

Transmission peak:  T>90%
Blocking range: 300-1000nm
Blocking depth: light pollution  line blocking >99%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
Parallelism: 30s

• Thickness 2mm (add 0.7mm to the back focus specification of a corrector)

  Multi-layer anti-reflection coating

  Non-cementing optical substrate coating

  Optolong L-Pro filter adopts precision coating based on Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL(central wavelength) no deviation affected by temperature change.

  Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band.