Methane band filter
The methane band filter is a dichroic filter with 50nm full width half maximum (FWHM) and a central wavelength of 880nm. You can use this filter to take images of the outer planets: The outer gaseous planets are very dark around 880nm as there is a strong absorption band of methane here. Due to this, the disks of the planets are very weak, nearly invisible. Using this filter, you may use much longer exposure times to capture faint moons, rings or ring fragments as they do reflect sunlight and have no absorption band.
This filter is not really suitable for beginners in planetary imaging. However, if you do own a larger instrument (> 10"/25cm) and a sensitive camera (e.g. a DMK from "The imaging Source" or comparable equipment) this filter will give you access to a large and interesting field of work!