The 6nm OIII CCD Narrowband Emission Line Filter
Mounted in Low Profile Non-Threaded 36mm Round Cell 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 CCD 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.

Now Mounted in Low Profile Non-Threaded Cell:

Sometimes unmounted filters can be hard to handle. The smaller diameters, such as this 36mm OIII filter, can be especially difficult to pick up and insert or remove from the filter wheel, and that can lead to possible damage as well as unwanted reflections from incorrectly installed filters. Astronomik has solved this problem by mounting their 31mm and 36mm filters in a low profile (3mm) non-threaded cell. O-rings, washers, or spacers are no longer required to hold the filter in place, and because the cell is only 3mm thick, it works well in all appropriately sized filter wheels. Mounted 31mm and 36mm Astronomik filters will also play nice with unmounted versions in the same carousel.

OPT Product Number: AK-OIIICCD6-36

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.