Product: SVBONY SV115 Telescope Filter O-III Filter Narrowband Cuts Light Pollution Filter for Astronomy Telescope (2 inch)
Brand: SVBONY
Narrowband OIII filter is designed for nebula observation allowing 18nm bandwidth of light centered on a wavelength of 500nm through, 
which corresponds to OIII emission lines, and reducing 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 and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow). Features:
 Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces. Suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants. Suitable for viewing on 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 filter 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, not brightening the nebula. Thin metal cells have a clear aperture of 26mm for 2" filters Each filter comes with a plastic case with high pressure EVA case lining Specification:
 Blocking area: 400-700nm
 Transmittance: 90% at 495.9nm and 500.7nm
 FWHM: 18±2nm
 Thickness: 1.85mm
 Surface quality: 60/40 (Refer to MIL-O-13830)
 Diameter:2 inch WARNING: 
 The filters are not designed for sun observation. DO NOT LOOK AT THE SUN WITH this FILTER. You would be BLIND if you fail to observe the warning. Package Includes:
 1 x SV115 O-III 2" filter
The O-III filter completely blocks virtually all other visible wavelengths of light so views of nebulas are optimized;increases contrast through selective filtration-Anti-reflection coated to prevent glaring and ghosting
The filter made from high-grade glass with dichroic interference and antireflection coatings;not only useful at light-polluted sites; the contrast is also increased at dark sky sites;it can be used with all 2" eyepieces
Narrowband filter 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, not brightening the nebula
The 2" O-III filter useful for large aperture telescopes through which the light of the Moon can be extremely overwhelming. Allowing just for the Double Ionized Oxygen lines between 495.9nm to 500.7nm to pass through at 90%
Astrophotographic;The filter enhances contrast during visual observation of gaseous and planetary nebulae in all sky conditions; 2" filter allows high-contrast imaging even in areas with strong light pollution

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