USED – Orion OIII Filter 1.25″ Orion

USED GEAR INFORMATION

This filter is in great condition

Overview

• Narrow band pass filter (11nm) isolates just the two doubly ionized oxygen lines (496nm and 501nm) emitted by planetary and extremely faint nebulae.
• • Produces near-photographic views of the Veil, Ring, Dumbbell, Orion, plus many other nebula.

Description

The Oxygen III Filters are the result of 20 years of steady design improvements, and continue to deliver the highest performance of all anti-light pollution filters obtainable today. The following information recommends which filter to use on which celestial objects, and explains how filter transmissions differ.

The legendary Orion 1.25″,2″ and 2″ Cassegrain, OIII narrow band-pass filters isolate just the two doubly ionized oxygen lines (496 and 501nm lines) emitted by diffuse, planetary and extremely faint nebulae. Thus, these faint objects become much more visible against the blackened background of space. The Orion Oxygen III Filter produces near-photographic views of the Veil, Ring, Dumbbell and Orion nebula, among many other objects. Performs well under both light-polluted and dark skies.

The legendary Orion Cassegrain OIII narrow band-pass filter threads onto your telescope’s SCT rear-cell, and presents male SCT threads for accessory attachment. The Cassegrain filter cell allows you to change eyepieces without threading/unthreading the filter, and is also easier to change-out than the standard 2″ filter cell with gloves on, for cold-weather observing.

Visually, the Orion 2″ Cassegrain OIII filter isolates just the two doubly ionized oxygen lines (496 and 501nm lines) emitted by diffuse, planetary and extremely faint nebulae. Thus, these faint objects become much more visible against the blackened background of space. The Orion Oxygen III Filter produces near-photographic views of the Veil, Ring, Dumbbell and Orion nebula, among many other objects. Performs well under both light-polluted and dark skies.

To ensure that your Orion filter remains the World’s Best, the strictest quality control standards are employed throughout the production process. Each Orion Oxygen III Filter is individually inspected and proudly inscribed with the percentage of light transmittance of the two OIII emission lines.

Objects	Examples	Best Filter for Viewing	Best Filter for Photography
Stars & Star Clusters	M13, M11	Deep Sky	Deep Sky
Diffuse Nebulae	Lagoon, Swan	OIII (light polluted sky) Deep Sky, UHC (dark sky)	Deep Sky
Planetary Nebulae	Dumbbell, Ring	OIII (light polluted sky) Deep Sky, UHC (dark sky)	Deep Sky
Faint Planetary Nebulae	NGC 7293, Abell 33, Jones 1	OIII	Deep Sky
Reflection Nebulae	Pleiades, Trifid	Deep Sky	Deep Sky
Spiral Galaxies	M33, M101	Deep Sky	Deep Sky
Faint Nebulae	Veil, Rosette, N. American	OIII (light polluted sky) Deep Sky, UHC (dark sky)	Deep Sky
Extremely Faint Nebulae	California, Horsehead	H-Beta	Night-Sky H-Alpha Deep Sky

Specifications

Exit Pupil Specifications:
The exit pupil of a telescope is a measure of specific magnification, which differs from absolute magnification, and which determines the surface brightness of an extended object image. Exit pupil diameter may be expressed as the quotient of eyepiece focal length divided by the telescope’s focal ratio. For example, a 32mm eyepiece used on an f/10 telescope will have a 3.2mm exit pupil. Each Orion filter has an optimum eyepiece exit pupil range shown below.

Filter Type	OIII
Bandpass	10-12nm
Optimum Exit Pupil (Light polluted sky)	2-5mm
Optimum Exit Pupil (Dark sky)	3-7mm

 Notice:
As filter bandpass decreases, optimum exit pupil size tends to increase. To determine the best eyepiece focal length to use with a given filter, simply multiply the Exit Pupil value shown above by your telescope’s focal ratio. For example, if you are using the Orion H-Beta filter at a dark site and your telescope has an f/6 focal ratio, the best range of eyepiece focal lengths to use with this filter is [(4 to 7) x 6] = 24mm to 42mm.

Filter Construction:
Orion nebula filters are made using thin-film dielectric coatings on optically flat glass. These exclusively designed dielectric coatings consist of over 30 alternating layers of several different materials. Each layer is about a wavelength of light thick and has a thickness accurate to 2 – 3
angstroms. The Deep Sky Filters use very hard electron-beam deposited coatings on one side of the glass substrate, and delicate anti-reflection coatings on the other. Except for the Deep Sky Filter, all Orion filter coatings are very hard, and may be cleaned carefully with alcohol. The UHC, OIII, and HBeta filters consist of two elements, sandwiched coatings, and anti-reflection coatings on all surfaces to prevent ghosting.

Mechanical Design:
These filters thread directly into most eyepieces and telescope accessories. Threads are standard for 1¼” filters. 48mm filters are standard for 2″ O.D. eyepieces.

Bandpass:
These Orion filters reject man-made and natural light pollution. Mercury light pollution occurs at 365, 405, 436, 546, 577, and 617nm. High-pressure sodium streetlights emit at 570, 583, 600, and 617nm. Natural airglow occurs at 558 and more weakly at 630nm. There is a window of greatly reduced light pollution from 440nm (blue) to 540nm (green). The Orion Deep Sky Filter has a wide 90-100nm bandpass for most of this range (441-535nm) to yield maximum transmission of light from stars and
galaxies. The UHC Filter has a narrow 22nm bandpass through 484-506nm. The OIII Filter has a very narrow 11nm bandpass for 495-501nm, and the H-beta Filter has the narrowest bandpass of all – only 8nm centered at 486nm. The narrower the bandpass, the higher the rejection of light pollution and the blacker the skies. However, a narrower bandpass also means fainter star images. Nevertheless, the Deep Sky Filter has high transmission for the photographic red nebula emission lines.

Nebula Emission Lines:
The main visible radiation from emission nebulae consists of doubly ionized oxygen near the wavelength of 500nm. There is also weaker emission due to hydrogen-beta at 486nm. The invisible but photographically important emission of red hydrogen-alpha and ionized nitrogen occur near 657nm.