Astronomik OIII 6 nm Clip-Filter EOS APS-C (Astronomik, SKU: 10201093) is a narrowband filter for imaging nebulae emitting light from doubly ionised oxygen OIII near 501 nm. Its 6 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 6 nm passband suppresses background and starlight more strongly than the 12 nm version. It is useful for faint nebulae, crowded star fields and cameras with low dark current. A narrower passband requires particular attention to the optical system’s focal ratio.
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.
Original Canon EF-S lenses are incompatible with the EOS APS-C filter installed. The filter works with suitable EF lenses and T2/M42 adapters. It can also be fitted inside the original Canon EF–EOS M adapter for EOS M cameras; this is different from direct EOS M filter mounting.
• passband: OIII, 6 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 6 nm Clip-Filter EOS APS-C
• protective filter box
• manufacturer: Astronomik
• manufacturer product code: 10201093
• type: OIII narrowband emission-line filter
• full width at half maximum (FWHM): 6 nm
• guaranteed transmission: over 88% at the main OIII line at 501 nm
• typical transmission: 92% at the main OIII line at 501 nm
• out-of-band blocking: from UV to IR
• coating: Astronomik MFR
• recommended focal ratio range: f/4–f/∞
• mount: Clip-Filter EOS APS-C
• compatible APS-C DSLR bodies: Canon EOS 7D, 7D Mark II, 20D, 20Da, 30D, 40D, 50D, 60D, 60Da, 70D, 77D, 80D, 90D, 100D, 200D, 250D, 300D, 350D, 400D, 450D, 500D, 550D, 600D, 650D, 700D, 750D, 760D, 800D, 850D, 1000D, 1100D, 1200D, 1300D, 1500D, 2000D, 3000D, 4000D
• incompatible: original Canon EF-S lenses; full-frame bodies and EOS-1D
• 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.
