ZWO 1.25" Methane Band CH4 Filter (ZWO-CH4) Flat Field and permanently programmable periodic error

and permanently programmable periodic error correction (PPEC)

Although masks have long been used as focusing aids

14") Filter diameter (internal): 100

Recommended for fine focus when doing astrophotography and/or use with HyperStar

but not the CPC Deluxe HD

ZWO 1.25" Methane Band CH4 Filter (ZWO-CH4) Flat Field and permanently programmable periodic errorThe ZWO Methane band (CH4) filter is a special filter for photographical use. Its FWHM is 20nm which is suitable for most IR sensitive colour or mono cameras. It can reveal the detail of the target and not too dark. It is recommended for planetary imaging such like Jupiter, Saturn and the other planets. This filter is a 1. 25(31. 7mm) filter and comes with an inner filter thread . It is protected in a plastic case.