Optolong OIII 6.5nm Narrowband Filter 36mm Unmounted (OPT-OIII-65NM-36MM) Manual Mount Housed in a 2" barrel

Housed in a 2" barrel like the 35mm

2") Secondary Mirror Obstruction by Diameter: 28% Secondary Mirror Obstruction by Area: 7

The Lunt ED refractors are designed to retrofitted with the LS50FHa Hydrogen-alpha Filter

The Bahtinov mask is used focus sma telescopes accurately

For a bit more than generic brands

Optolong OIII 6.5nm Narrowband Filter 36mm Unmounted (OPT-OIII-65NM-36MM) Manual Mount Housed in a 2" barrelOptolong improved extra Narrowband OIII CCD 6. 5nm filter is designed for nebula observation allowing 6. 5nm 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 vapour, and both high and low pressure sodium vapour lights and the unwanted natural light caused by neutral