Optolong O-III 25nm Light Pollution Filter

The O-III 25nm filter is designed for nebula observation.  It transmits 25nm bandwidth, centered on a wavelength of 500nm, which corresponds to OIII emission lines.  It also reduces the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high and low pressure sodium vapor lights, as well as the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).

The OIII filter emits 495.9nm and 500.7nm.  It is a blue-green colored filter. Many images of planetary nebula and supernova remnants are taken only with H-alpha and OIII filters. They show great structural details, but have natural colors, looking like an RGB image.

Main Use and Performance

• Suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants.
• Suitable for viewing bright nebulae like M42 Orion Nebula in heavy light pollution.
• Use with a large aperture telescope under clear and dark viewing conditions with good seeing.
• Narrowband filters do not eliminate the effects of light pollution or increase the object’s brightness. In many cases, they increase the contrast between nebula and night sky, without brightening the nebula.

Technical Data

• Schott substrate material
• Thickness 2.0mm
• Surface Quality: 60/40 (Refer to MIL-O-13830)
• Fine-optically polished to ensure accurate 1/4 wavefront and <30 seconds parallelism over the both surfaces
• 90% transmission at major OIII line 495.9nm and 500.7nm
• Precision off-band blocking,  specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm). 

Coating Parameter

• Non-cemented optical substrate coating
• Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength); no deviation affected by temperature change
• Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band

Filter Cell

• Ultra-thin filter cell minimizes vignetting by maximizing possible clear aperture (clear aperture is 26mm for 1.25”; 45mm for 2”)
• Aerometal Material
• Precise CNC Machining
• Sand Blasting Process
• Black Anodized Finish
• Extinction Treatment to Prevent Reflection
• Laser Engraving No Fading

Package

• Plastic PP Case
• Imported High Pressure EVA Case Lining
• Silver Cardboard Box
• High Density Sponge Carton Lining

Sizes

• Standard 1.25”
• Standard 2”
• Round 36mm Unmounted