A. About Optolong's L-eXtreme Filter

The Optolong 1.25” L-eXtreme filter builds on the success of the renowned L-eNhance filter to deliver an even higher degree of contrast when imaging emission nebulae, planetary nebulae, and supernovae remnants. The L-eXtreme is two filters in one. It has a narrow 7nm passband centered on H-alpha at 656nm and a second 7nm passband centered on OIII near 501nm. The majority of nebulae have their strongest emission at these two wavelengths.

Unlike the L-eNhance filter, the L-eXtreme blocks the weaker H-beta emission line at 486nm to deliver more contrast in the fainter regions of nebulae, even in light-polluted sky. The narrower passbands of the L-eXtreme are especially important in blocking moonlight and broadband light pollution found in many urban and suburban centers.

The L-eXtreme is an ideal filter for use with DSLRs, one-shot color (OSC), and monochrome CCD and CMOS cameras, especially with fast optical systems. It’s an indispensable filter for urban and suburban astrophotographers and for everyone who likes to extend their imaging sessions into nights when the moon is bright.

B. Spectral Curve Transmission Characteristics

• FWHM: 7nm at O-III and 7nm at H-a
• Blocking range: 300 - 1000nm
• Light pollution line blocking depth: > 99%

C. Technical Specifications

• Both surfaces are fine optically polished, accurate to 1/4 wavelength or better, and parallel to within 30 seconds or arc.
• 1.85mm thick Schott B270 optical glass substrate material.
• Very high surface quality of 60/40 or better (US Military Spec MIL-O-13830).

D. Optical Coating Specifications

• Multi layer anti-reflection coated.
• Non-cementing optical substrate coating.
• Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) so that there is no deviation due to temperature changes during use.
• Precise and homogeneous coatings ensure high values of desired passband and blocking of unwanted offband.
• Every single filter is tested and passed by Optolong before shipping to dealers.

E. Other

• 1.25" astronomy filter with standard M28.5x0.6 male filter thread (no female thread, so it cannot be stacked with other filters).
• Ultra-thin filter cell to minimize vignetting; clear optical aperture of 26mm.
• Precision CNC-machined metal filter cell with sand blasted black anodized finish, anti-reflection treatment, and laser engraving.
• High quality protective plastic storage case.

WARNING: Optolong filters are not designed for direct solar observation. NEVER use these filters for observing the Sun, or permanent eye and equipment damage will result.