The 6nm OIII MFR Narrowband Emission Line Filter
Canon EOS Full Format XL Clip by Astronomik:

Astronomik OIII Narrowband Filters are suitable for false color imaging of emission nebulae emanating doubly ionized oxygen (OIII). The contrast between an object glowing at 501nm and the background is increased significantly due to the high transmission and effective out-of-band blocking!

The OIII line (501nm) is in the blue-green portion of the spectrum. Planetary nebulae and supernova remnants are considered emission nebulae, since they produce their own light, and so objects like the Ring, Dumbbell, Veil, and Crab nebulae are common targets using OIII filters since doubly ionized oxygen is the main emission for these interesting objects.

This Astronomik OIII MFR Narrowband filter has a 6nm FWHM. The extra narrow bandpass of 6nm filters are most appreciated with cameras that offer extremely low dark current and good cooling, or when imaging in areas with severe light pollution. The higher level of out-of-band blocking allows you to take longer exposures and choose objects embedded in normally over-bright, crowded areas of the Milky Way. Extra blocking causes faint stars to disappear from the background, and brighter stars will be pin-pricks of light.

Astronomik MFR Narrowband Emission Line Filter Highlights:

• Special Coatings Allow Filter Use Across Most Focal Ratios: Astronomik Narrowband Emission Line filters have been designed to be used with a wide range of focal ratios. The special MFR (multi-focal ratio) coatings applied to the 12nm FWHM filters make them compatible with optics as fast as f/3, and the 6nm models perform well with focal ratios as fast as f/4. This means you won't need to buy different filters for your fast refractor and your SCT, and you won't have to pay premium prices for high-speed filters.
• Amazingly High Out of Band Blocking: Astronomik Narrowband Emission Line Filters offer superb blocking of unwanted wavelengths, from UV up to IR. Transmission of 90-percent is guaranteed by Astronomik, but the typical transmission can be as high as 96-percent on both 6nm and 12nm Narrowband filters. This feature translates to extremely high contrast and pleasingly dark background skies, even under heavily light-polluted conditions, allowing you to take longer exposures if you so desire without creating an overly bright (or saturated) background. Another benefit of good out-of-band blocking is the reduction of stray light and halos. Stars display as sharp points of light on a velvety black background, providing the perfect backdrop for the deep-sky object you are imaging.
• Image During Full Moon or Under Light Polluted Skies: Because Astronomik Narrowband Emission Line Filters have a high transmission rate for the chosen wavelength but blocks pretty much everything else, you can image from your own backyard, even if your neighborhood suffers from light-pollution (which is pretty much everybody). If it is a beautiful night with great seeing but the Moon phase does not support visual deep-sky astronomy, you can pull out your telescope, camera, and Astronomik filters and still get great results.

• Compatible Canon cameras:
• - 5D Mk I (no live view)
• - 5D Mk II
• - 5D Mk III
• - 6D Mk I
• Non-compatible cameras:
• - 5DS
• - 5DSR
• - 5D Mk IV
• - 6D Mk II
• - Canon APS-C (EF-S) cameras
• - Canon Mirrorless cameras

OPT Product Number: AK-OIIICCD6-XL

Please Note: Clip-Filters:

Clip-in EOS XL filters are for these Canon Full-Format Cameras:  5D Mark II, 5D Mark III, and 6D Mark I.  (5D Mark I will work without LiveView only) 

The Astronomik XL Clip filters will not work with the Canon 6D Mark II, 5DS, 5DSR, the 5D Mk IV camera bodies, and will only work without LiveView in the Canon 5D Mk I.

Ten Year Warranty! Astronomik filters will last for many years without degradation of the coatings, due to the quality of the substrate and coatings used. The high-quality glass is optically polished and is free of stress and striae. The coatings used on Astronomik filters are applied in multiple layers, making the resulting filter scratch resistant and unaffected by moisture or aging that some filters of less quality may be prone to. Astronomik filters are also parfocal due to the small thickness tolerance allowed. Astronomik backs up this quality with a ten-year warranty.