Astronomik OIII 12 nm Clip-Filter Sony alpha 7 (Astronomik, SKU: 10205092) is a narrowband filter for imaging nebulae emitting light from doubly ionised oxygen OIII near 501 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 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.
Slight corner shading caused by the tight Sony bayonet can be corrected with flat-field frames. After the session, remove the filter and keep it in its box; the manufacturer advises against leaving it permanently in the camera.
• passband: OIII, 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 MFR
• mounting inside a compatible camera, in front of the sensor
• durable coatings resistant to scratching and moisture
• filter: Astronomik OIII 12 nm Clip-Filter Sony alpha 7
• protective filter box
• filter removal tool
• manufacturer: Astronomik
• manufacturer product code: 10205092
• type: OIII narrowband emission-line filter
• full width at half maximum (FWHM): 12 nm
• guaranteed transmission: over 90% at the main OIII line at 501 nm
• typical transmission: 95% at the main OIII line at 501 nm
• out-of-band blocking: from UV to IR
• coating: Astronomik MFR
• recommended focal ratio range: f/3–f/∞
• mount: Clip-Filter Sony alpha 7
• compatible bodies: Sony Alpha 7, 7 II, 7 III, 7 IV, 7 V, 7C, 7C II, 7CR, 7R, 7R II, 7R III, 7R IV, 7R V, 7S, 7S II, 7S III, 9, 9 II, 9 III
• incompatible bodies: Sony Alpha 58, 68, 77, 99, 6000 and A-mount DSLRs
• incompatible lenses: Sigma 14 mm F1.4 DG DN Art; Sony FE 12–24 mm f/2.8 GM (SEL1224GM)
• 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 OIII imaging helps reveal nebular structure with a reduced sky-background contribution.
