Astronomik SII 12 nm MaxFR Clip-Filter EOS R APS-C (Astronomik, SKU: 10220224) is a narrowband filter for imaging nebulae emitting light from ionised sulphur SII at 671.7 nm and 673.0 nm. Its 12 nm full width at half maximum increases the contribution of the selected emission relative to the sky background, both at dark sites and under light pollution.
The filter suppresses light outside the useful passband, from UV to IR. It can be used for monochrome imaging or to build composites from exposures taken through several emission-line filters. Exposure time and channel balance depend on the brightness of the individual lines, camera sensitivity and sky conditions.
The 12 nm passband preserves more starlight than narrower versions, which can help when guiding uses light passing through the filter. It is a useful entry into narrowband imaging; a narrower passband does not always help when the exposure background is mainly limited by camera noise.
The MaxFR coating is intended for fast optics with low f-numbers. The recommended range is f/1.7–f/6; at f/1.4, the manufacturer specifies about 85% of maximum transmission. This is a relative value, not an absolute transmission of 85%.
The Clip mount places the filter inside a compatible camera body, in front of the sensor. This allows the same filter to be used with different compatible lenses or a telescope and reduces dust settling on the sensor. The correct version must be selected for both the camera model and the lens.
• passband: SII, 12 nm full width at half maximum
• suppression of unwanted out-of-band light from UV to IR
• recording of one emission-line channel for later combination
• coating: Astronomik MaxFR
• mounting inside a compatible camera, in front of the sensor
• durable coatings resistant to scratching and moisture
• filter: Astronomik SII 12 nm MaxFR Clip-Filter EOS R APS-C
• protective filter box
• filter removal tool
• manufacturer: Astronomik
• manufacturer product code: 10220224
• type: SII narrowband emission-line filter
• full width at half maximum (FWHM): 12 nm
• guaranteed transmission: over 90% at both SII lines
• typical transmission: 96% at both SII lines
• sulphur lines (SII): 671.7 nm and 673.0 nm
• out-of-band blocking: from UV to IR
• coating: Astronomik MaxFR
• recommended focal ratio range: f/1.7–f/6
• transmission at f/1.4: about 85% of the maximum
• mount: Clip-Filter EOS R APS-C
• compatible bodies: Canon EOS R7, R10, R50, R50 V, R100
• incompatible lenses and teleconverters: Canon RF 14 mm f/1.4 L VCM, RF 28 mm F2.8 STM, RF 35 mm F1.8 IS Macro STM, RF 85 mm F1.2L USM; Canon Extender RF 1.4x, RF 2x
• 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
• quality control: individual measurement of spectral response
Selective SII imaging helps reveal nebular structure with a reduced sky-background contribution.
