FILTER SPECIFICATIONS & USES
LUMICON Nebula Filters
The Deep Sky, Hydrogen-Beta, Oxygen-III, and Ultra High Contrast 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.
Deep Sky Filter
- Intended for viewing nebulae from light-polluted skies
- Blocks all mercury vapor and high & low pressure sodium vapor lamp light, neon lights, and airglow, while transmitting the rest of the visible spectrum
- The best all-around visual light pollution filter for use in urban skies
- This filter also provides high-contrast views of the Martian polar caps
Ultra-High Contrast Filter
- Narrow bandpass filter (24 nm) isolates the two doubly ionized oxygen lines (496 and 501 nm) and the hydrogen-beta line (468 nm) emitted by planetary and most emission nebulae
- Provides superb views of the Orion, Lagoon, Swan and other extended nebulae
- The best all-around dark-sky nebular filter available
Oxygen-III Filter
- Narrow bandpass filter (11 nm) isolates just the two doubly ionized oxygen lines (496 and 501 nm) emitted by planetary and extremely faint nebulae
- Produces near-photographic views of the Veil, Ring, Dumbbell, Orion, plus many other nebulae
Hydrogen-Beta Filter
- Extremely narrow bandpass filter isolating the hydrogen-beta line alone (486 nm)
- Excellent for viewing the Horsehead, Cocoon and California Nebulae
- Often the only way to view certain nebulae
- Best used under clear skies with large aperture
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 32 mm eyepiece used on a f/10 telescope will have a 3.2 mm exit pupil. Each Lumicon filter has an optimum eyepiece exit pupil range shown below.
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 Lumicon 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] = 24 mm to 42 mm.
Filter Construction:
Lumicon 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 Lumicon filter coatings are very hard and may be cleaned carefully with alcohol. The UHC, O-III, and H-Beta 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 1.25" filters. 48 mm filters are standard for 2" O.D. eyepieces.
Bandpass:
These Lumicon filters reject man-made and natural light pollution. Mercury light pollution occurs at 365, 405, 436, 546, 577, and 617 nm. High-pressure sodium streetlights emit at 570, 583, 600, and 617 nm. Natural airglow occurs at 558 and more weakly at 630 nm. There is a window of greatly reduced light pollution from 440 nm (blue) to 540 nm (green). The Lumicon Deep Sky Filter has a wide 90-100 nm bandpass for most of this range (441-535 nm) to yield maximum transmission of light from stars and galaxies. The UHC Filter has a narrow 22 nm.
Nebula Emission Lines:
The main visible radiation from emission nebulae consists of doubly ionized oxygen near the wavelength of 500 nm. There is also weaker emission due to hydrogen-beta at 486 nm. The invisible but photographically important emission of red hydrogen-alpha and ionized nitrogen occur near 657 nm.
LUMICON Color and Neutral Density Filters
The Lumicon Color and Neutral Density Filters are made from renowned Schott and Hoya optical glass and allow for maximum contrast on viewing planetary and lunar detail. Individually precision ground, highly polished with maximum light transmission coatings on both sides, these filters are 100% guaranteed for life.
For information on planetary/color filter applications, please refer to below:
