Andover Corporation

General Specifications for Nebula filters

Review of Andover's nebula filters on ScopeReviews.com

Selecting the correct nebula filter for your viewing application can be quite confusing. There are many different types of nebula filters available, such as narrowband, wideband, O-III and H-beta types. The filters that Andover offers are the narrowband and O-III types, which in our opinion are the best types for viewing emission and planetary nebulae. Andover does not offer the wideband and H-beta filters since the wideband filter does the least of any nebula filter to enhance the emission and planetary nebulae and the H-beta filter is best used when viewing specialized nebulae such as the Horsehead Nebula, California Nebula and a few others.

			Three Channel Nebula Filter
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.
			O-III Nebula Filter
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.
		Physical Specifications   31mm dia. 50mm dia. Mounting: threaded eyepiece threaded ring Construction: Laminated filter Laminated filter Outside diameter: 31.0mm +0/-.12mm 50.0mm +0/-.12mm Clear Aperture: 24.1mm dia. 45mm dia. Thickness: 10.0mm +0/-.5mm 8.2mm +0/-.5mm Thread size: 1-1/8 - 40 M48 - 0.75
		Optical Specifications   Transmitted Wavefront: 3-5 waves per 25mm Parallelism: 1 arc minute or better Surface Quality: 80/50 or better per MIL-C-675 A/R coatings: BBAR on all exterior surfaces Durability: Per MIL-C-48497A, moderate abrasion Spectral Data: Spectral bandpass curve supplied
		Part Numbers and Pricing (click for price and availability)   31mm dia. 50mm dia. 3-channel nebula filter: Nebula-NB-31 Nebula-NB-50 O-III nebula filter: Oxygen-III-31 Oxygen-III-50