Pellucid Spectra OIII nebula filter 2 in, observatory grade

Specifications

Description

The Spectra OIII is a line filter in a 2 in threaded cell that passes a 12 nm band centered on the doubly ionized oxygen lines at 496 and 501 nm. It blocks almost everything else, which makes the sky background very dark and isolates nebulae that shine strongly in oxygen light.

Planetary nebulae and supernova remnants respond especially well. The Veil Nebula in Cygnus shows long, braided filaments that are hard to see without a filter. The Owl Nebula, the Helix Nebula, and the Crescent Nebula all show more shape and extent. Small planetary nebulae can be easier to find, because they stay bright while the stars around them dim.

Because the passband is narrower than that of a UHC filter, the OIII filter dims the view more. It works best in telescopes of 200 mm aperture or larger, where enough light remains to see detail. In smaller telescopes, a UHC filter often gives a better overall view.

A useful technique is to blink the filter: hold it between the eyepiece and your eye, then move it in and out of the light path. Faint planetary nebulae stand out because they stay at the same brightness while stars around them dim.

The filter is made on polished optical glass with hard-sputtered coatings and anti-reflection layers on both faces. The 2 in cell threads into eyepieces, diagonals, and filter wheels.

The Spectra OIII suits observers with medium and large telescopes who want to see supernova remnants and planetary nebulae in more detail.

About this configuration

The Pellucid Spectra OIII nebula filter 2 in 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. With anti-reflection layers on both sides, less light bounces between the filter and the eyepiece or camera sensor.

The filter ships in a clear plastic case that keeps dust off the glass between sessions. The 2023 edition uses the same coating design as later years, with small differences in the cell markings. Check the size in the specifications against your eyepiece barrels, star diagonal, or filter wheel before you choose.

What's in the box

• OIII filter in 2 in threaded cell
• Padded storage pouch
• Test report with measured transmission curve
• Plastic storage case

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter wheels (M48 x 0.75).
• Most effective in telescopes of 200 mm aperture and larger.