Chroma SII Ha OIII 3 nm f/3 Filter Set, 50x50 mm unmounted

Chroma Narrowband Filters with 3 nm Bandwidth, optimized for f/3

These nebula filters from Chroma offer extreme contrast. Thus, the astrophotographer achieves a very good result even with considerable stray light from cities or from the moon. The high transmission is given at focal ratios between f2.8 and f/3.6.

The set consists of filters for three spectral lines:
H-alpha filters are essential for imaging nebulae which are rich in ionized hydrogen. At 656.3 nm, a narrow-band emission filter is required to separate H-alpha from the [S II] doublet (671.6 nm and 673.1 nm). This line is the strongest and most important emission in most nebulae.

OIII filters isolate the 500.7 nm primary emission line of doubly ionized oxygen [O III]. After H-alpha, this is the next most common emission when imaging nebulae, it is only emitted where the radiation from the star that causes the nebula to glow has a high energy and oxygen is present.

SII filters isolate the spectral emission of singly ionized sulfur atoms [S II], also common in nebulae. Emission is at two lines occurring as a doublet, at 671.6 and 673.1 nm. This filter also separates sulfur emission from H-alpha emission (656.3 nm). The line is preferably used as a supplement to [O III] and H-alpha in order to generate SHO tri-color images.

The quality features of these narrowband filters at a glance:

High light transmission and narrowest bandwidth to maximize contrast

Use in light-polluted areas and dark locations

Extends exposure time in moonlight conditions

These narrow band filters can be used with systems from f/2.8 to f/3.6 with virtually no signal loss

A consistent filter thickness of 3.0 mm ensures parfocality