iOptron OIII Narrowband Filter -1.25"

The iOptron OIII Narrowband Filter is crafted for astrophotography and deep‑sky observation, designed to precisely isolate the characteristic green‑blue emission lines of doubly‑ionized oxygen (O III) at 495.9 nm and 500.7 nm.
By allowing these key wavelengths to pass while strongly rejecting most other wavelengths—such as artificial light sources (mercury‑ and sodium‑vapor lamps) and natural skyglow—the filter significantly enhances contrast and reveals fine structural details in emission nebulae.

Key Features:

• Standard 1.25″ mounted size (≈ 31 mm) compatible with most 1.25″ filter wheels and eyepiece holders (threaded M28.5×0.6).

• Precision optical construction: high surface quality (60/40), surface flatness better than λ/4, and parallelism around 30″.

• Multi‐layer anti‑reflection coating to maximize transmission of the target wavelengths and minimize reflections and ghosting.

• Specifically tuned for O III emission: passes the 495.9 nm and 500.7 nm lines while blocking much of the unwanted broadband light, improving nebula‑to‑sky contrast.

• Clear warning: Not designed for solar viewing. Never use this filter for direct or imaging of the Sun.

Why It Stands Out:
This filter is ideal for astrophotographers focused on emission nebulae or planetary nebulae where the O III line dominates. Because it isolates the “blue‑green” oxygen emission, it allows you to capture dramatic contrast between faint nebular structures and background sky, especially under light‐polluted conditions. When combined with H‑alpha or S II filters, it becomes a powerful component in narrowband imaging workflows.

Typical Use Cases:

• Mounted in a 1.25″ filter wheel (such as the iOptron iEFW series) for monochrome camera imaging of emission nebulae.

• Use with a telescope and camera setup to isolate the oxygen emission of planetary nebulae, supernova remnants or regions rich in O III signal.

• Great for creating multi‐filter images: for example using H‑alpha + O III to produce stunning two‑channel or full RGB‐style narrowband results.

• For visual use (with a 1.25″ eyepiece) to boost contrast of nebulae in a telescope under ambient skyglow or light pollution.

Important Notes:

• Using the filter does not increase the brightness of the object—it improves contrast. As stated by iOptron: “Narrowband filters do not eliminate the effects of light pollution or increase the object’s brightness; in many cases they increase the contrast between nebula and night sky.”

• Always ensure proper mounting and that your filter wheel or holder is securely threaded in; the optical quality only pays off if it is well aligned.

• Because the filter is narrowband, exposure times may need to be longer than with broadband filters, particularly for fainter objects.

• Confirm compatibility with your imaging train (e.g., sensor size, optical back‑focus, filter thickness) to avoid vignetting or field shift.

• “Isolate the O III emission lines at 495.9 nm & 500.7 nm for dramatic nebula contrast.”

• “Premium 1.25″ narrowband filter built for deep‑sky imaging of emission nebulae.”

• “Precision coatings and optical flatness ensure clean, high‑contrast results.”