Meade Series 4000 Photo-Visual Color Filter: #25A Red

The #25A Red (14% transmission) Filter: strongly blocks the transmission of blue and blue-green wavelengths, resulting in very sharply defined contrast between, for example, blue tinted cloud formations on Jupiter and the lighter-toned features of the disk.  This filter is also useful for the delineation of the Martian polar ice caps and maria.  Due to its relatively low total light transmission, the #25A filter should only be employed on telescopes of 8" aperture or larger.

The use of a Meade Series 4000 color filter can mean the difference between seeing small craterlets in the floor of Clavius on the Moon and not; it can mean the difference between seeing five or six whirls, festoons, and loops in Jupiter's north equatorial belt and seeing one or two; it can mean the difference between seeing the inner crépe ring of Saturn and not.  Depending on atmospheric conditions on both the Earth and the planet being observed, the advantages of color filters can be anywhere from subtle to dramatic.

For increased contrast and resolution of the Moon and planets in visual or photographic applications color filters are an essential tool of the lunar and planetary observer.  These color filters permit the observation and photography of surface detail that is often virtually invisible without filtration.  Filters solve or greatly reduce the effects of two basic observing problems: (a) Irradiation is the blurring of a boundary between lighter and darker areas of the Moon or a planetary surface and can be caused either by the effects of highly contrasting light impacting the human eye or by the motion of the Earth’s atmosphere, through which the observation is being made. (b) Contrast is the separation of adjacent surface regions according to their color; for example, a light green area on Mars can become mixed in the eye with an adjacent light yellow area, to the effect that the combined area appears yellow-green, not separated into its component regions.

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.  Each filter glass is anti-reflection coated on both sides and is mounted in a machined aluminum cell with the Wratten No. of the filter marked on the side of the cell.  Filters may be piggybacked, or stacked, to achieve selective filtration of the visual color spectrum.  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 the attached 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.