Focal Length Calculator. Tele Vue Optics, founded in 1977, has been thrilling amateur astronomers since 1979. The Newtonian Telescope Design Planner uses "JavaScript" to perform the mathematical calculations; therefore, your browser must be "JavaScript" compatible and enabled. Power The power of the telescope, computed as focal length of the telescope divided by the focal length of the eyepiece. Focal Length & Ratio Useful calculators and formulae. Calculate the focal ratio of your telescope… It is our mission. Aperture: mm. f/ Please select one of 458 telescopes from the drop-down box, or use Manual mode to enter the aperture and focal length by … Two versions of the planner … Type of telescope Focal Ratio Calculator. X Focal Ratio: f/ = Focal Length: mm. High powers are useful for detecting faint stars, use up to 50X or 75X per inch if seeing conditions permit. It's in the materials we choose, the designs we create, the craftsmanship we demonstrate...the images … Telescope Aperture The diameter of the objective lens or mirror. Formula: Aperture X Focal Ratio . Calculate the focal length of your telescope. The edge support configurations have been selected after extensive discussions and represent the state-of-the-art ideas about the edge support in mirror cells for Dobsonian telescopes from a number of … Telescope Calculator ... Focal Ratio Please enter the focal ratio of your telescope.