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HOW TO SELECT TELESCOPE FILTERS

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Nebula Filters

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


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 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.

Oxygen III Filter

  • 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.

Hydrogen-Beta Filter

  • 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.

Comet Filter

  • 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

90nm

22-26nm

10-12nm

8-10nm

Optimum Exit Pupil (Light-polluted sky)

0.5-2mm

1-4mm

2-5mm

3-7mm

Optimum Exit Pupil (Dark sky)

1-4mm

2-6mm

3-7mm

4-7mm

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 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 Lumicon filters 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 Lumicon Filter

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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