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, /*C*and*C*/ supernovae remnants. The L-eXtreme is two filters in one. It has a narrow 7nm passband centered on H-alpha at 656nm /*C*and*C*/ 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 /*C*and*C*/ broadband light pollution found in many urban /*C*and*C*/ suburban centers.

The L-eXtreme is an ideal filter for use with DSLRs, one-shot color (OSC), /*C*and*C*/ monochrome CCD /*C*and*C*/ CMOS cameras, especially with fast optical systems. It’s an indispensable filter for urban /*C*and*C*/ suburban astrophotographers /*C*and*C*/ 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 /*C*and*C*/ 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 /*C*or*C*/ better, /*C*and*C*/ parallel to within 30 seconds /*C*or*C*/ arc.
• 1.85mm thick Schott B270 optical glass substrate material.
• Very high surface quality of 60/40 /*C*or*C*/ 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 /*C*and*C*/ resistance to scratching, as well as stability on CWL (central wavelength) so that there is no deviation due to temperature changes during use.
• Precise /*C*and*C*/ homogeneous coatings ensure high values of desired passband /*C*and*C*/ blocking of unwanted offband.
• Every single filter is tested /*C*and*C*/ 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, /*C*and*C*/ laser engraving.
• High quality protective plastic storage case.

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