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438 EUR
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price without VAT: 356 EUR
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Astronomik OIII 4nm 36 mm Filter (SKU: 8h11us / 10206336) is a high-end narrowband emission filter designed for astrophotography of oxygen-rich nebulae. It significantly enhances contrast by isolating the OIII emission lines at 496 nm and 501 nm, 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 outside the OIII lines across the entire ultraviolet (UV) to infrared (IR) spectrum. It removes emissions from sodium (Na) and mercury (Hg) street lamps, natural airglow, and most moonlight, enabling high-contrast imaging of faint nebular structures.
In locations with low light pollution, image background noise is often limited by the sensor’s dark current rather than by sky brightness. In such cases, further background suppression does not necessarily reveal additional object detail. Nevertheless, the OIII 4 nm filter remains an excellent choice for imaging extremely faint structures in star-dense regions and under 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 typically the first choice, enabling detailed imaging of red emission nebulae even during full Moon conditions. The OIII filter expands imaging capabilities to green and blue structures characteristic 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-rich 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 larger number of guide stars is required.
Astronomik MFR coatings provide excellent blocking from UV to IR, extremely high contrast, minimal scattered light, and no halos around bright 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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