Astronomik CLS 2" filter (Astronomik, SKU: 10213200) is a filter that reduces the effects of light pollution in deep-sky observing and astrophotography. It suppresses characteristic sodium and mercury lamp lines while transmitting broad regions of visible light and important nebular emission lines.
Its wider passbands than a UHC filter preserve more starlight. CLS can shift colour balance, so imaging data require appropriate calibration. The filter does not block infrared: a camera without its own IR cut-off needs additional filtration or the CLS-CCD version.
The filter has a 2" cell with an M48 × 0.75 thread. It fits accessories with a matching filter socket; the nominal cell size is not the diameter of the clear glass aperture.
• broad passbands transmitting the H-beta, OIII and H-alpha lines
• suppression of sodium and mercury lamp lines
• less stellar dimming than UHC filters
• durable coatings resistant to scratching and moisture
• filter: Astronomik CLS 2" filter
• protective filter box
• manufacturer: Astronomik
• manufacturer product code: 10213200
• transmission bands: 450–540 nm and above 650 nm
• transmission: 92% at 486 nm, 496 nm and 501 nm; 97% at 656 nm
• infrared blocking: none
• cell size: 2"
• thread: M48 × 0.75
• glass thickness: 1 mm
• material: finely polished optical glass
• optical quality: diffraction-limited
• coating resistance: to scratching, moisture and ageing
• parfocality: with standard Astronomik filters using 1 mm glass
CLS helps reduce sky background brightness while preserving a broad range of signal from the objects being imaged.
