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.