The Optolong 7nm Narrowband filter sets includes the following items:
- Optolong H-alpha 7nm
- Optolong OIII 6.5nm
- Optolong SII 6.5nm
The H-Alpha, Oxygen-III and Sulphur-II narrow-band filters boost the contrast of emission nebulae and supernova remnants for professional results, even under a bright sky affected by light pollution. This filter is used in combination with the OIII and SII filter to compose a narrowband colour image.
The 7nm band pass (6.5nm for OIII & SII) is only 2% of the entire visible spectrum, increasing the signal to noise ratio and delivering high contrast images and extremely dark backgrounds. The maximum transmission is above 80% and the transmission off band is only 0.1%. This is a value often undisclosed by other filter producers and it is critical to darken the sky background and minimise the halos around the stars. The filter cuts off the ultraviolet and infrared light so there is no need to use the IR-cut filter.
Every Optolong filter is marked with its unique serial number and individual passing band certificate. This test is rarely provided by any producer and it is a standard for high quality filters.