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723 EUR
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price without VAT: 588 EUR
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Astronomik OIII 4nm 50 mm Filter (SKU: 8h11tw / 10206350) is a premium narrowband emission-line filter designed for astrophotography of oxygen-rich emission nebulae. It significantly enhances contrast by isolating the OIII emission lines at 496 nm and 501 nm while effectively suppressing the sky background under both light-polluted and dark-sky conditions.
With an extremely narrow 4 nm bandwidth, the filter efficiently blocks unwanted light across the entire ultraviolet (UV) to infrared (IR) spectrum, including emissions from sodium (Na) and mercury (Hg) street lamps, natural airglow, and most moonlight. This results in high-contrast images with excellent separation of faint nebular structures, even in challenging observing environments.
In areas with very low light pollution, image background noise is typically limited by the sensor’s dark current rather than sky brightness. In such conditions, further background suppression does not necessarily reveal additional object detail. Nevertheless, the 4 nm version remains an excellent choice for imaging extremely faint structures in star-rich regions or from locations with severe light pollution.
Astronomik narrowband filters are among the most effective tools for deep-sky astrophotography in light-polluted environments. An H-alpha filter is usually the first choice, enabling detailed imaging of red emission nebulae even under full Moon conditions. The OIII filter expands imaging possibilities to green and blue structures typical of planetary nebulae, star-forming regions, and supernova remnants. Completing the set with an SII filter allows the creation of HSO false-color images similar in style to those produced by the Hubble Space Telescope.
The 4 nm and 6 nm OIII filters are ideal for imaging very faint objects in star-dense regions of the Milky Way and are recommended for cameras with extremely low dark current or for use under heavy light pollution. The 12 nm version is designed for typical DSLR cameras and CCD sensors with normal or higher dark current and is often preferred when a higher number of guide stars is required.
Astronomik MFR coatings provide excellent blocking from UV to IR, extremely high contrast, minimal scattered light, no halos, and sharp, well-defined stars. The OIII 4 nm filter with MFR coating can be used in optical systems with focal ratios from f/4.5 to f/15 without noticeable performance loss. MaxFR coatings are specifically designed for very fast optical systems; OIII 4 nm filters with MaxFR coating are currently under development.
• OIII emission lines: 496 nm and 501 nm
• bandwidth: 4 nm
• guaranteed transmission: >88% at the main OIII line (501 nm)
• typical transmission: approx. 92%
• glass thickness: 1 mm
• blocking range: UV – IR
• coating: Astronomik MFR
• parfocal with other Astronomik filters
• diffraction-limited performance
• resistant to humidity and aging
• individual quality control with spectrophotometric measurement
• supplied in a durable Astronomik filter box
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