The OIII filter is used for the observation and photography of gas nebulae in which doubly ionised oxygen fluoresces – primarily planetary nebulae and supernova remnants. This filter provides 97% transmission for the emission line at 500.7 nm, so that practically only the light from the nebula is transmitted. At the same time, this filter can be used for photography with virtually any aperture ratio from f/1.8 to f/12 without causing transmission of the H-beta line. This makes the Super-G filter ideal for use in areas with high light pollution as well as under dark skies. It can also be used on small telescopes, especially with large exit pupils and low magnification.
Photographic use: The OIII filter is also ideal for photographic use on all telescopes, especially with a DSLR or an astronomical OSC colour camera. For monochrome cameras, we recommend the even narrower Narrowband (6.5 nm) and Ultra-Narrowband (4 nm) filters, which are available specially adapted for different aperture ratios. For the comparatively broadband 9 nm filter, preshifting at focal ratios faster than f/4 is not necessary; it can be used at all focal ratios.
What does Super-G mean? The filter has the same thickness as the mounted LRGB filters from Baader. This makes it ideal for use as a "Super-G filter": In the transmission window of the normal green filter (490-580 nm), there are no other emission lines except OIII, and H-beta at 486 nm is covered by the RGB blue filter. When using the 9 nm O-III filter instead of the RGB green filter, emission nebulae are therefore much more pronounced, while the stars appear weaker.
The filter offers all the advantages of CMOS-optimised Baader filters:
- Increased contrast, tailored to typical CMOS quantum efficiency and s/n ratio
- Reflex-Blocker™ coatings for maximum insensitivity to retro-reflection from nearby auxiliary optics, even under the most adverse conditions
- Identical filter thickness to existing standards, with the utmost care taken to ensure homofocality
- Blackened edges all around, with filter front indicator in the form of a black outer edge on the telescope side to additionally prevent any reflection from light falling on the filter edge
- Each filter is individually precision-polished and coated, with a sealed coating edge (NOT cut from a larger plate, which would leave the coating edges exposed).
- Life-Coat™: even harder coatings to enable an age-resistant coating with an unlimited service life – even in the most adverse environments
