Color filters are an essential tool of the lunar and planetary observer, for filters permit the observation and photography of surface detail that is often virtually invisible without filtration. Meade Series 4000 filters are a large 26mm in clear aperture and are manufactured from the purest crown optical glass, dyed in the mass (not ''color coated''); there are no finer filters available for telescopic applications. For visual applications Series 4000 filters thread into the barrels of all Meade 1.25'' eyepieces, and into the barrels of virtually all other 1.25'' eyepiece brands as well. The eyepiece with filter can be placed in the eyepiece holder of a Schmidt Cassegrain telescope or Meade ED Apochromatic Refractor for Tele Extender eyepiece projection photography of the Moon and planets. The filters also thread into the barrels of the Meade Camera Adapter (1.25'') and Variable Projection Camera Adapter. Each Series 4000 filter is packed in a foam fitted plastic case for secure long term storage. Set #1 (4 filters) includes: #12 Yellow; #23A Light Red; #58 Green; #80A Blue.