A. About Optolong's L-Pro FIlter

The Optolong L-Pro (L-Professional) broadband filter is designed to improve the visibility of various deep sky objects. It does this by:

• Selectively reducing the transmission of wavelengths of light pollutants, specifically those produced by artificial lighting (including mercury vapor lamps, both high & low pressure sodium vapor lights, and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow)).
• Being highly transparent to the main nebula emission lines at OIII (496nm and 500nm), H-beta (486nm), NII (654nm and 658nm), H-alpha(656nm) as well as SII (672nm)

Unlike other light pollution filters such as UHC and CLS, the L-Pro is multi-bandpass filter which offers better color balance by maximizing the transmission band. The balanced transmission allows astrophotos to be taken with minimal color cast in broadband emission objects such as galaxies, reflection nebulae and globular star clusters. L-Pro is an excellent choice for light pollution suppression.

B. Main Uses and Performance

• Suitable for enhancing the contrast and details for both visual and photograghic purpose at urban and suburban areas with heavy light pollution.
• Suitable for color CCD cameras and unmodified DSLRs.
• Works well on most emission nebulae, reflection nebulae and dark nebulae.
• L-Pro filter has a very low transmission reduction rate against continuous spectrum space objects, and thus is quite effective in suppressing light pollution sources when shooting galaxies, reflection nebulae and globular star clusters. The same holds true for visual star observations.

C. Spectral Curve Transmission Characteristics

• High transmission of main nebula emission lines:
• H-beta 486.1nm, OIII 495.9nm and 500.7nm, H-alpha 656.3nm, and SII 672nm.
• Precise and high blocking of major transmission lines of artificial light pollution:
  • Hg (Mercury) at 435.8nm, 546.1nm, 577nm, and 578.1nm.
  • Na (Sodium) at 598nm, 589.6nm, 615.4nm, and 616.1nm.
• It also blocks out infrared wavelengths (700-1100nm) so a separate IR cut-off filter is not required for imaging applications.

D. Technical Specifications

• Both surfaces are fine optically polished, accurate to 1/4 wavelength or better, and parallel to within 30 seconds or arc.
• 2mm thick Schott B270 optical glass substrate material.
• Very high surface quality of 60/40 or better (US Military Spec MIL-O-13830).

E. 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.

F. Other

• 2" astronomy filter with standard M48x0.75 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 45mm.
• 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.