This is a 1.25" #80A Medium Blue filter. It is in excellent condition with very minor brassing on the threads from use.
·Primarily used for enhancing the boundaries of features in the upper atmosphere of Jupiter, such as festoons in the belts and the Great Red Spot;
·very useful during violet clearing on Mars;
·improves the observation of faint dusky features on Mercury at twilight when the planet is near the horizon;
·increases contrast on dark shadings of upper Venusian clouds;
·brings out the best definition of comet gas tails;
·very useful as a lunar filter under dark sky conditions
Will sell for $10 shipped to you. Money order, cash or Paypal ok.