Pellucid Spectra OIII imaging filter 36 mm, observatory grade

Specifications

Description

The Spectra OIII imaging filter is a narrowband filter on an unmounted 36 mm round glass, designed for filter wheels used with monochrome astronomy cameras. Its 6.5 nm passband is centered on the 501 nm line of doubly ionized oxygen.

Narrowband imaging isolates the light of specific elements in emission nebulae. Combined with hydrogen-alpha and sulfur-II filters, an OIII filter lets you assign each element to a color channel and build false-color images that show the structure of a nebula. Even a single OIII channel shows features such as the outer shells of planetary nebulae and the filaments of supernova remnants.

A narrow passband blocks moonlight and light pollution very effectively, so narrowband imaging works from cities and on nights with a bright Moon. The 6.5 nm width balances blocking with exposure time: narrower filters block more but need longer exposures.

The 36 mm size covers sensors up to about APS-C in typical filter wheel setups. With fast optical systems, a narrow passband shifts toward shorter wavelengths for light that arrives at an angle, so the filter is designed for systems of f/3.5 and slower.

The glass is polished flat with hard-sputtered coatings on one side and an anti-reflection coating on the other. That keeps halos around bright stars small, which matters when you stack many exposures.

The filter handles normal cleaning with a soft brush and lens fluid. Store it in its case between sessions, since unmounted glass edges chip if they hit a hard surface.

The Spectra OIII imaging filter suits imagers who already use a monochrome camera and want to add oxygen data to hydrogen-alpha images.

About this configuration

The Pellucid Spectra OIII imaging filter 36 mm is offered in several configurations, and the notes below describe what this particular one includes. The observatory grade comes with a measured transmission curve for the individual filter in the box. Observatory grade glass has the tightest flatness tolerance in the Spectra line, which suits imaging with long focal lengths. Hard-sputtered layers keep their passband stable over time, which matters if you compare images taken years apart.

A plastic case is light and stacks with other filter cases in an accessory box. The passband in the 2024 edition matches the other years; the changes concern the housing only. The transmission figures in the specifications apply to every configuration of the Spectra line.

What's in the box

• OIII imaging filter, unmounted 36 mm round
• Padded storage pouch
• Test report with measured transmission curve
• Plastic storage case

Compatibility notes

• Fits filter wheels and holders that accept 36 mm unmounted filters.
• Designed for optical systems of f/3.5 and slower.
• Covers sensors up to about APS-C size in typical filter wheel spacing.