Optolong OIII filter

Optolong Narrowband OIII Filter – High-Contrast Oxygen-III Filter for Nebula Observation & Imaging

The Optolong Narrowband OIII Filter is a precision-engineered oxygen-III filter developed specifically for nebula observation and deep-sky astrophotography. Designed by Optolong, this filter allows an 18nm bandwidth of light centered at 500nm to pass through—precisely matching the OIII emission lines at 495.9nm and 500.7nm.

By selectively transmitting OIII wavelengths while blocking more than 99% of artificial light pollution, including mercury vapor, high-pressure and low-pressure sodium street lights, as well as unwanted natural skyglow caused by atmospheric oxygen, the Optolong OIII filter delivers dramatically improved contrast and fine nebular detail. The result is darker skies, cleaner backgrounds, and nebula structures that stand out with exceptional clarity—even from light-polluted urban environments.

Planetary nebulae and supernova remnants are particularly rich in OIII emissions. Many iconic deep-sky images are captured using OIII and H-alpha filters together, producing results that retain natural, RGB-like colors while revealing extraordinary structural detail.

Main Applications & Use Cases

• ✔ Visual observation & astrophotography of emission nebulae

• ✔ Excellent for planetary nebulae and supernova remnants (e.g. Veil Nebula)

• ✔ Highly effective on bright nebulae like M42 Orion Nebula, even under heavy light pollution

• ✔ Best used with large aperture telescopes under clear, dark skies and good seeing conditions

Important Note: Narrowband filters do not increase the brightness of objects. Instead, they increase contrast between the nebula and the night sky, making faint details easier to observe and image.

Optolong OIII – Optical Characteristics

• Bandwidth: 18nm

• Central Wavelength (CWL): 500nm

• Substrate: Optical glass

• Thickness: 1.85mm

• Average Transmission (Tave): >80%

• Blocking Range: 400–700nm

• Blocking Depth: Light pollution line blocking >99%

• Surface Quality: 60/40

• Transmitted Wavefront RMS: λ/4

• Parallelism: 30s

These specifications ensure excellent sharpness, high contrast, and minimal optical distortion, making the filter suitable for both visual observers and demanding astrophotographers.

Advanced Coating Technology

Optolong uses state-of-the-art coating processes to ensure durability and optical precision:

• ✔ Multi-layer anti-reflection coatings for maximum light transmission

• ✔ Non-cemented optical substrate coating for long-term stability

• ✔ Ion-assisted deposition coating technology for superior scratch resistance and durability

• ✔ Stable central wavelength (CWL) with no deviation due to temperature changes

• ✔ Planetary rotation coating system ensures coating homogeneity, high pass-band transmission, and strong off-band optical density

⚠️ WARNING – Solar Safety

Optolong filters are NOT designed for solar observation.
⚠️ DO NOT look at the Sun with this filter. Doing so may cause permanent blindness.

Why Buy Optolong OIII Filter from Modern Telescopes?

Buy with confidence from Modern Telescopes – India’s largest and most trusted telescope selling company. We supply 100% genuine Optolong filters, expert technical guidance, fast pan-India shipping, and reliable after-sales support for amateur and professional astronomers across India.