Orion 5599 1.25-Inch Mars Observation Eyepiece Filter High-performance observational eyepiece filter markedly improves views of Mars Fully-coated Mars filter increases contrast to bring out subtle details on the disc of the red planet When using the Mars filter on a clear, dark evening you'll see polar ice cap detail, subtle mare shadings, duststorm and cloud activity Eyepiece filter dramatically improves views of Mars even in smaller astronomical telescopes Designed to fit 1.25" telescope eyepieces with filter threads. Metal filter cell construction.