Chroma Technology 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 maximize transmission.

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 apertures of f/4 or higher. For faster optical systems please use the special high-speed filter set.

This set consists of three filters, all of which have 3nm Bandpass:

• H-alpha (27001) 
• SII (27009)
•  OIII (27006)

SII filters isolate the spectral emission of singly ionized sulphur 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 sulphur emission from H-alpha emission (656.3nm).

H-alpha filters are essential for imaging nebulae and other objects which are rich in ionized hydrogen. At 656.3nm, a narrow-band emission filter is required to separate H-alpha from the SII doublet (671.6nm and 673.1nm).

OIII filters isolate the 500.7nm primary emission line of doubly ionized oxygen. After H-alpha, this is the second most common emission when imaging nebulae.

Chroma Technology filters are available in the following sizes:

• 1.25″ Mounted
• 2″ Mounted
• 31mm Unmounted
• 36mm Unmounted
• 50mm Unmounted
• 50x50mm Square Unmounted

Optical Density Data:

All transmission and blocking (OD) data are actual, measured spectra of representative production lots. Spectra varies slightly from lot to lot. Optical density values in excess of 6 may appear noisy because such evaluations push the resolution limit of low light level measurements.