Optolong 2'' L-eXtreme Dual Narrowband Filter [OPTO-L-EXTREME-2]

The Optolong 2" L-eXtreme Dual Band filter is a 7nm bandpass filter that isolates the H-Alpha and Oxygen III emission lines to maximize the signal-to-noise ratio between nebulae. When compared to the Optolong L-eNhance tri-band filter, the dual band only emits the Ha and OIII emission lines rather than the L-eNhance filters transmission of Hb, Ha, and OIII. Optolong has ensured that the L-eXtreme filters do not transmit between H-beta and OIII lines, as there are no nebula lines there. Limiting the transmission this way means that light pollution is blocked so nebula signals are boosted and the background of the sky becomes darker for better contrast during imaging. For those who live in areas with higher levels of light pollution or for those who would like to image during times where the Moon is bright, this threaded L-eXtreme filter is an excellent tool for their astrophotography toolbox!
When it comes to quality control Optlong ensures that each filter is examined by Spectrophotometer and Laser Interferometer for spectrum characteristics and surface accuracy respectively. During the manufacturing process, high-precision grinding and polishing is used to ensure that the substrate parallelism is greater than 30" and the surface accuracy is better than λ/4. Electron-beam gun evaporation and Ion-assisted deposition (IAD) coating is applied to provide durability and resistance to scratching. IAD increases film firmness, consolidates membrane compactness, and changes vacuum coating material characteristics. This type of manufacturing technology also provides stability on the central wavelength so there is no deviation during temperature changes.

L-eXtreme Dual Band Filter Specifications
Substrate: B270
Filter Size: 2"
Thickness: 1.85mm
FWHM: OIII 7nm+Ha 7nm
Blocking range: 300-1000nm
Blocking depth: light pollution line blocking >99%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
Parallelism: 30s