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

All configurations of the Pellucid Spectra OIII nebula filter 2 in share the same filter glass design; the options change the grade, the coating, and the case. 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. The standard coating is applied to the filter side of the glass, with a single anti-reflection layer on the back.

The padded pouch protects the filter from knocks and fits in a jacket pocket at the telescope. The passband in the 2024 edition matches the other years; the changes concern the housing only. 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
• Padded pouch

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.