- Extremely narrow bandpass filter isolating the hydrogen-beta line alone (486nm).
- Excellent for viewing the Horsehead, Cocoon and California Nebulae.
- Often the only way to view certain nebulae.
- It is best used under clear skies with large aperture.
The Hydrogen-Beta 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.
Also known as the Horsehead Nebula filter, the Lumicon 1.25", 2", and 2" Cassegrain H-beta Filter isolates only the hydrogen-beta line of the spectrum (486nm) in a narrow pass-band just 9 nm wide, providing maximum contrast. Now you can view extremely faint nebulous objects such as the Horsehead, Cocoon and California Nebulae. In many cases, the Lumicon Hydrogen-Beta Filter is the ONLY way to view these objects. Recommended for 8" or larger telescopes.
The Cassegrain filter-cell 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.
Now you can view extremely faint nebulous objects such as the Horsehead, Cocoon and California Nebulae. In many cases, the Lumicon Hydrogen-Beta Filter is the ONLY way to view these objects. Recommended for 8" or larger telescopes.
To ensure that your Lumicon filter remains the World's Best, the strictest quality control standards are employed throughout the production process. Each Lumicon Hydrogen - Beta Filter is individually inspected and proudly inscribed with the percentage of light transmittance of the H-Beta emission line.
|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
|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
|California, Horsehead||H-Beta||Night-Sky H-Alpha
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 Lumicon filter has an optimum eyepiece exit pupil range shown below.
|Optimum Exit Pupil (Light polluted sky)||3-7mm|
|Optimum Exit Pupil (Dark sky)||4-7mm|
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] = 24mm to 42mm.
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, OIII, and HBeta filters consist of two elements, sandwiched coatings, and anti-reflection coatings on all surfaces to prevent ghosting.
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.
These Lumicon 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 Lumicon 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.