The Deep Sky, Hydrogen-Beta , Oxygen III , and Ultra High Contrast Filters
are the result 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.
Objects |
Examples |
Best Filter for Viewing
|
Best Filter for Photography
|
Stars & Star Clusters |
M13, M11 |
None |
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 |
None |
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 |
- 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
- Narrow band pass filter (24nm) isolates the two doubly ionized
oxygen lines (496 and 501nm) and the hydrogen-beta line (486nm)
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.
- 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.
- 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.
- Designed to enhance the cyanogen (CN) frequency found in
comet tails..
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 filter has an optimum eyepiece exit pupil range
shown below.
Filter Type |
Deep Sky |
UHC |
OIII |
H-Beta |
Bandpass |
|
|
|
|
Optimum Exit Pupil (Light-polluted
sky) |
|
|
|
|
Optimum Exit Pupil (Dark sky) |
|
|
|
|
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 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
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. nebula filters
include anti-reflection coatings on both sides to prevent ghosting
and increase light transmittance. They also have a hard, electron-beam
deposited coating for mechanical protection. While still delicate,
filters may be carefully cleaned with isopropyl alcohol, or
Lumicon's Advanced Cleaning Kit.
Mechanical Design
These filters thread directly into most eyepieces and telescope accessories.
Threads are standard for 1.25 filters. 48mm filters are standard for 2"
O.D. eyepieces.
Bandpass
These 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 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.
Color and Neutral Density Filters
The 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 are 100% guaranteed for
life.
| #8 Light Yellow
Moon: Feature Contrast
Mars: Maria
Jupiter: Belts
Jupiter: Orange-Red Zonal
Uranus: Dusky Detail
Neptune: Dusky Detail
#11 Yellow-Green
Mars: Maria
Jupiter: Clouds
Jupiter: Red/Blue Contrast
Saturn: Clouds
Saturn: Cassini Division
Saturn: Red/Blue Contrast
#12 Yellow
Moon: Feature Contrast
Mars: Blue-Green Areas
Jupiter: Red-Orange Features
Saturn: Clouds
Saturn: Red-Orange Features
#15 Dark Yellow
Moon: Feature Contrast
Mars: Clouds
Mars: Polar Caps
Jupiter: Belts
Saturn: Belts
Uranus: Dusky Detail
Neptune: Dusky
Detail #21 Orange
Mars: Maria
Jupiter: Belts
Jupiter: Polar Regions
Saturn: Belts
Saturn: Polar Regions
#23A Light Red
Mercury: Planet/Sky Contrast
Mars: Maria
Mars: Blue-Green Areas
Jupiter: Belts
Jupiter: Polar Regions
Saturn: Belts
Saturn: Polar Regions |
#25 Red
Mercury: Features
Venus: Planet/Sky Contrast
Venus: Terminator
Mars: Maria
Mars: Polar Caps
Jupiter: Belts
Jupiter: Galilean Moon Transits
Saturn: Clouds
#29 Dark Red
Mercury: Features
Venus: Planet/Sky Contrast
Venus: Terminator
Mars: Maria
Mars: Polar Caps
Jupiter: Belts
Jupiter: Galilean Moon Transits
Saturn: Clouds
#38A Dark Blue
Venus: Clouds
Mars: Dust Storms
Jupiter: Belts
Jupiter: Great Red Spot
Jupiter: Disc
Saturn: Belts
#47 Violet
Venus: Clouds
Mars: Polar Caps
Saturn: Rings
#56 Light Green
Moon: Detail
Mars: Dust Storms
Mars: Polar Caps
Jupiter: Belts
Jupiter: Atmosphere
Jupiter: Red/Blue/Light Contrast
#58 Green
Venus: Clouds
Mars: Polar Caps
Jupiter: Red/Blue/Light Contrast
Saturn: Belts
Saturn: Polar Regions |
#80A Blue
Moon: Feature Contrast
Jupiter: Belts
Jupiter: Rilles
Jupiter: Festoons
Jupiter: Great Red Spot
Saturn: Belts
Saturn: Polar Regions
#82A Light Blue
Moon: Low-Contrast Features
Mars: Low-Contrast Features
Jupiter: Low-Contrast Features
Saturn: Low-Contrast Features
ND13 Neutral Density
13% Transmission
Moon: Glare Reduction
Double Stars: Bright Primary
ND25 Neutral Density
25% Transmission
ND50 Neutral Density
50% Transmission
Single Polarizing Filter
Rotating Polarizing Filter
Moon: Glare Reduction or Variable Transmission |
Object |
Features |
Recommended |
Mercury |
Planet/Sky Contrast |
#23A Light Red
|
|
Features |
#25 Red
#29 Deep Red |
Venus |
Clouds |
#38A Deep Blue
#47 Violet
#58 Green |
|
Planet/Sky Contrast |
#25 Red
#29 Deep Red |
|
Terminator |
#25 Red
#29 Deep Red |
Moon |
Detail |
#56 Light Green |
|
Feature Contrast |
#8 Light Yellow
#12 Yellow
#15 Deep Yellow
#80A Blue |
|
Low Contrast Features |
#82A Light Blue |
|
Glare Reduction |
ND13 Neutral Density |
Mars |
Clouds |
#15 Deep Yellow |
|
Maria |
#8 Light Yellow
#15 Deep Yellow
#11 Yellow-Green
#21 Orange
#23A Light Red
#25 Red
#29 Deep Red |
|
Blue-Green Areas |
#12 Yellow
#23A Light Red |
|
Dust Storms |
#38A Deep Blue
#56 Light Green |
|
Polar Caps |
#15 Deep Yellow
#25 Red
#29 Deep Red
#47 Violet
#56 Light Green
#58 Green
Deep Sky Filter |
|
Low Contrast Features |
#82A Light Blue |
Jupiter |
Clouds |
#11 Yellow-Green |
|
Belts |
#8 Light Yellow
#15 Deep Yellow
#21 Orange
#23A Light Red
#25 Red
#29 Deep Red
#38A Deep Blue
#56 Light Green
#80A Blue |
|
Rilles |
#80A Blue |
|
Festoons |
#80A Blue |
|
Atmosphere |
#56 Light Green |
|
Red-Orange Features |
#12 Yellow |
|
Orange-Red Zonal |
#8 Light Yellow |
|
Red/Blue Contrast |
#11 Yellow-Green |
|
Blue/Light Contrast |
#25 Red |
|
Great Red Spot |
#38A Deep Blue
#80A Blue |
|
Galilean Moon Transits |
#25 Red
#29 Deep Red |
|
Red/Blue/Light Contrast |
#56 Light Green
#58 Green |
|
Polar Regions |
#21 Orange
#23A Light Red |
|
Disc |
#38A Deep Blue |
|
Low Contrast Features |
#82A Light Blue |
Saturn |
Clouds |
#11 Yellow-Green
#12 Yellow
#25 Red
#29 Deep Red |
|
Belts |
#15 Deep Yellow
#21 Orange
#23A Light Red
#38A Deep Blue
#58 Green
#80A Blue |
|
Polar regions |
#21 Orange
#23A Light Red
#58 Green
#80A Blue |
|
Rings |
#47 Violet |
|
Cassini Division |
#11 Yellow-Green |
|
Red/Blue Contrast |
#11 Yellow-Green |
|
Red/Orange Features |
#12 Yellow |
|
Low Contrast Features |
#82A Light Blue |
Uranus |
Dusky detail |
#8 Light Yellow
#15 Deep Yellow |
Neptune |
Dusky detail |
#8 Light Yellow
#15 Deep Yellow |
Double Stars |
Bright Primary |
ND13 Neutral Density |
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