Astronomik OIII visual filter

The Astronomik OIII visual filter is tailored for observation of OIII regions, particularly effective in both light-polluted or dark sky areas.

The Astronomik OIII visual filter significantly enhances the contrast between objects emitting light at the OIII emission lines and the sky background. Specifically designed for gaseous and planetary nebulae, the Astronomik OIII visual filter features a narrow pass band for both OIII lines, ensuring substantial contrast gains even under optimal observation conditions. This attribute makes a critical difference in detecting faint supernova remnants and planetary nebulae, often revealing details that might otherwise be imperceptible.

The filter’s application spans aperture ratios from 1:3.5 to 1:15, most suitable for telescopes starting at 6" (150mm) aperture.

The filter blocks the emission lines of high- and low-pressure sodium (Na) and mercury (Hg) vapour lamps, the maxima of typical LED lights, and all lines of natural airglow. It allows the OIII lines to pass through with high transmission. This selective filtering enhances the contrast between celestial objects and the sky background, which is crucial for all visual observations.

Overall, the Astronomik OIII visual filter excels in enhancing the visibility and detail of OIII emission regions. It is an indispensable tool for astronomers aiming to maximize the observational potential of gaseous and planetary nebulae.

Suitability of the Astronomik OIII visual filters

• Visual observation (dark skies): Very good, huge contrast enhancement for OIII-emission nebulae
• Visual observation (urban skies): Very good, huge contrast enhancement for OIII-emission nebulae

Technical Data

• Typical transmission of 95% at 496nm (OIII)
• Typical transmission of 95% at 501nm (OIII)
• Transmission range: 494nm to 506nm
• Full-Width-Half Maximum (FWHM): 12nm
• Glass thickness: 1mm (except Astronomik OWB Type 3 and XT filters)
• Finely polished optical glass, free of any striae, residual stresses, and bubbles
• Extremely scratch-resistant and durable coating
• Completely resistant against high humidity and aging effects
• Parfocal with other Astronomik filters
• Diffraction-limited
• Optimized spectral windows
• Delivered in a high-quality, long-lasting filter box
• Made in Germany

Astronomik filters are diffraction-limited, ensuring that the optical performance (resolution and contrast) of your telescope is not compromised. Thanks to the high-precision machining of the glas substrate, all Astronomik filters are parfocal. The wedge errors are far below all common tolerances. Therefore, all issues concerning focal distances and the exact alignment of images from each color channel are effectively eliminated.

Every Astronomik filter undergoes a rigorous quality control process before delivery. Additionally, each Astronomik Narrowband-Emissionline filter is measured using a high-end PerkinElmer Spectrophotometer to ensure it meets the specifications published on our website. On the back of each Narrowband-Emissionline filter box, you will find a label detailing the precise spectral data for that specific filter, including the maximum transmission and the recommended range of focal ratios for best performance of that specific filter.

Customer opinion

John C.: »I bought your 2'‘ visual OIII filter from OPT and found it superior to the others I have tried. No red dots. Excellent contrast in the veil nebula. Thank you for making such a fine filter!«