A. About Optolong's Variable Polarizer Filter

A variable polarizing Moon filter consists of two single polarizing filters coupled together. One of these has threads to attach to the bottom of eyepieces or other threaded adapter barrels, and the second filter can freely rotate over 360-degrees, thus allowing you to control the brightness of the image over a wide range. You simply rotate the lower filter until the image brightness is pleasing and comfortable for you, given your telescope aperture and the phase of the Moon. While primarily meant for use while observing the Moon, this filter can also help with observations of other bright objects like Venus and Jupiter. Please note, however, that unlike some other similar filters on the market, the two Optolong filter components of this item cannot be separated.

B. Technical Specifications

• All surfaces are fine optically polished, accurate to 1/4 wavelength or better, and parallel to within 30 seconds or arc.
• 2mm thick Schott B260 optical glass substrate material.
• Very high surface quality of 60/40 or better (US Military Spec MIL-O-13830).

C. 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.

D. Other

• 1.25" astronomy filter with standard M28.5x0.6 male filter thread.
• 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.