Optolong O-III Swanband Filter 6.5 nm, unmounted D=50 mm

Optolong O-III Deep-Sky Filter 6.5 nm, round Disc with 50 mm Diameter

Extra Narrowband OIII 6.5 nm filter is designed for nebula observation allowing 6.5 nm bandwidth of light centered on a wavelength of 500 nm through, which corresponds to [O III] 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 (skyglow).

OIII emits 495.9 nm and 500.7 nm, resulting in a blue-green colored filter. Many of 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 photographing on faint emission nebulae in full moonlight or in severe light pollution

Hubble look of images can be made by the combination of H-alpha, OIII and SII, such as the famous “Pillars of Creation” (M16 Eagle Nebula)

Narrowband imaging with SHO set (H-alpha, OIII and SII) can be done with the moon up in heavy light pollution, so your equipment is not sitting dormant for several weeks

Which side of the filter needs to face towards the telescope?

Optolong has a good explanation on their page with a check on unmounted filters. With mounted filters, it´s easy. The side with the external thread must face the camera.

Link to iOptron page: Should Optolong filters be installed in a certain orientation? (external link)
You can download the generated PDF from our own server.