Chroma SII 3nm Filter 36mm Unmounted

Chroma SII filters isolate the spectral emission of singly ionised sulfur atoms, 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 (656.3nm).

About Chroma

Chroma Technology is an employee-owned company based in Vermont, USA. Chroma manufacture the highest quality astronomy filters with durable, sputtered hard coatings using single substrates of the best glass, eliminating the need for laminations. All primary filter coatings are applied on the front surface and anti-reflection coatings on the rear surface to prevent ghosting and to maximise transmission. Chroma astronomical filters are used worldwide in research and amateur applications. 

Highly precise and accurate, the passbands of these filters remain spectrally stable and do not drift in response to extreme temperature fluctuations or changes in humidity.

All filters may be used with focal ratios of f/4 or slower. For optics faster than f/4 then due to the spectral shift we recommend using the 5nm filters instead.

Features of the Chroma SII Filter

CWL: 672.4nm, Bandwidth: 3nm

• Durable sputter coatings
• Parallelism: <30 arcsec
• Thickness: 3.0 +/-0.05mm
• Filters designed for use with CCD and for f/4.0 or slower
• Transmitted wavefront better than 0.25 waves/inch
• No reflections leading to image distortions or ‘back reflections’