Optolong 31mm Unmounted Filter Set with H-Alpha, SII, and OIII Filters – HASIIOIII-31U Optolong

Optolong 31mm Unmounted Filter Set with H-Alpha, SII, and OIII Filters

This filter gives you Optolong’s 3 best-selling deep-sky filters at an affordable price. This 31mm filter set features the best-selling 7nm Hydrogen-Alpha filter, 6.5nm Sulfur-II filter, and 6.5nm Oxygen-III filter. All filters have a 31mm aperture and come unmounted.

Each filter in the Optolong 31mm Unmounted Filter Set is made with Schott glass that has been multi-coated with an ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength or CWL. This filter set is designed to be used in color filter wheels that accept 31mm unmounted filters. It doesn’t matter which way you drop them into the filter wheel. The filters are unmarked and either side can face up or down.

Optolong 7nm H-Alpha Filter – The Optolong H-Alpha 7nm is an extremely narrow emission-line filter that works by allowing a 7nm bandwidth of light, centered on the 656nm wavelength through, and blocking the transmission of contrast-killing light pollution wavelengths. Wavelengths that are responsible for natural light pollution, or skyglow, are drastically reduced, as is artificial light pollution caused by high and low-pressure sodium vapor and mercury vapor lights. The result is a high contrast image that reveals the H-alpha line in all its glory.

Optolong 6.5nm SII Filter – The Optolong Sulfur-II 6.5nm Extra-Narrowband Filter transmits a 6.5nm bandwidth of light that is centered at 672nm and drastically reduces other transmissions, including wavelengths of light that are responsible for light pollution (both artificial and natural). Like all Optolong filters that are designated as “CCD”, this SII filter also blocks infrared wavelengths from 700nm to 1100nm so you don’t need a separate IR-Cut filter.

Optolong 6.5nm OIII Filter – The Optolong Oxygen III 6.5nm Extra-Narrowband Filter transmits a 6.5nm bandwidth of light that is centered at 500nm and drastically reduces other transmissions, including wavelengths of light that are responsible for light pollution (both artificial and natural). Like all Optolong filters that are designated as “CCD”, this OIII also blocks infrared wavelengths from 700nm to 1100nm so you don’t need a separate IR-Cut filter.