* Astronomy

Blobrana · L

RE: Wratten #25 Filter

Blobrana · L

The Moon shot with red filter

Clavius Orion Maksutov cassegrain telescope 180/2700

Clavius with Orion Mak180 with a DMK21 camera Astronomik red filter and takahashi LE 7.5mm eyepiece

Blobrana · L

A Wratten #25 (or Cokin #003 Red) red filter will block all other wavelengths of light below 580 nm. The filter will enhance contrast on Mars, Jupiter, and Saturn and solar (with a solar filter) features.

A red eyepiece filter, such as the Wratten #25, will darken a sunspot umbra, causing it to stand out against the solar disc. For an observer interested in the statistical counting of sunspots, this is a helpful tool for locating weak detached portions of umbrae, an umbra in the early developmental stage, or pores. A red filter is also known to increase contrast within a sunspot's penumbra.
Source

A Wratten #29 Dark Red filter (6100-7000A) is suitable for sunspot imaging.

Colour	Recommended minimum aperture
#25A Red (14% transmission): (3 stops)	80mm Aperture	The #25A filter strongly blocks the transmission of blue and blue-green wavelengths, resulting in a very sharply defined contrast between blue-tinted cloud formations on Jupiter and the lighter-toned features on the disc. Also useful for delineation of the Martian polar ice caps and maria. Because of its relatively low total light transmission, the #25A should be employed on telescopes of 8" aperture or larger.