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Three Channel Nebula Filter
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There are two types of nebulae that we are interested in viewing: emission nebulae and planetary nebulae. Emission nebulae occur when a star is born and planetary nebulae occur when a star is dying. The Andover Three Channel Nebula Filter works very well for viewing both types of nebulae. A true nebula filter works by blocking out the sky glow (artificial light pollution) and enhancing deep sky objects. Most all commercially available nebula filters do decrease the sky glow, but in doing so many of them decrease the brightness of stars and star clusters. The Andover Three-Channel Nebula Filter is unique: First it blocks the sky glow and enhances the nebulae, secondly it lets through a selected band of blue light which enhances the viewing of star clusters, and finally it transmits the Hydrogen-Alpha line which is very important for photographing emission nebulae. Two standard sizes are available, 31mm and 50mm, both of which are mounted in special threaded rings. Custom sizes and mounting are available; contact our technical sales department if you have a custom requirement.
"The Andover Nebula-NB-50" is a wonderful filter! Magic on all deep sky objects. Planets show more details, and color correction is incredible." - Paolo Candy, Ph.D., Director of the Cimini Astronomical Observatory, Italy
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O-III Nebula Filter
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The O-III Nebula Filter has a narrower bandpass than the Andover Three Channel Nebula Filter. The narrow bandpass of the O-III Filter blocks out a lot of the sky glow (artificial pollution) and isolates the two O-III lines centered at 496.9nm and 500.7nm. This filter produces a significant increase in contrast and is best suited for viewing Planetary Nebula.
"The Andover Oxygen-III-50, under full moon and light pollution, displays more visible features on Planetary Nebulae than any other filter I have seen." - Paolo Candy, Ph.D., Director of the Cimini Astronomical Observatory, Italy
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Physical Specifications
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31mm dia. |
50mm dia. |
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Mounting:
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threaded eyepiece |
threaded ring |
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Construction:
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Laminated filter |
Laminated filter |
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Outside diameter:
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31.0mm +0/-.12mm |
50.0mm +0/-.12mm |
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Clear Aperture:
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24.1mm dia. |
45mm dia. |
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Thickness:
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8.2mm +0/-.5mm |
8.2mm +0/-.5mm |
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Thread size:
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1-1/8 - 40 |
M48 - 0.75 |
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Optical Specifications
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Transmitted Wavefront:
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3-5 waves per 25mm
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Parallelism:
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1 arc minute or better
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Surface Quality:
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80/50 or better per MIL-C-675
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A/R coatings:
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BBAR on all exterior surfaces
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Durability:
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Per MIL-C-48497A, moderate abrasion
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Spectral Data:
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Spectral bandpass curve supplied
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