With most professional telescopes, you will have to remove it every now and then in order to recalibrate. A Barlow lens spreads light out and increases a telescope’s focal length. Most of us know how to compute the visual magnification of our telescope when using an eyepiece: Divide the focal length of the telescope by the focal length of the eyepiece. It does so by magnifying the image. The magnification is the telescope focal length divided by the eyepiece focal length, in millimeters. For example, a 1,000-mm telescope with a 20-mm eyepiece gives a relative magnification to our eye of 50× when looking through the eyepiece. Several factors affect the magnification of the telescope then, you can decide what should be the magnification of an ideal telescope for you. In this article, I’m going to show you how to increase the magnification of a telescope, specifically the one in the picture above. The role of the lens is to reflect, while the role of the eyepiece is to give a closer and more detailed look. This feature can be manipulated using different combinations of objective and eyepiece lens. The magnification of a telescope and eyepiece is very simple to calculate. Magnification = Telescope focal length ק Eyepiece focal length. So, a 14″ telescope used at 40x gives an exit pupil of 9mm. The magnification of a telescope is measured by dividing the diameter of the objective lens over the focal distance of the telescope. In general, when the magnification of scope increases, the image brightness, and field of view (FOV) decreases. Increasing Telescope Magnification with a Barlow Lens. For example, if you use a telescope of 1000mm focal length with a 25mm eyepiece, the magnification would be 40x (1000mm ק 25 = 40). If the focal length of the objective is “F” and the focal length of the eyepiece is “f”, then the magnification of the telescope/eyepiece combination is F/f. Below the minimum magnification, the effect is to stop down the aperture. An additional thing you can do to expand the magnification of your telescope further, is to add a Barlow Lens. Telescope Magnification Formula. The result is that the image being observed is magnified. For example, a 4″ telescope has a minimum magnification of 14x. An 8″ telescope has a minimum of 29x, and a 14″ telescope has a minimum of 50x. For example, a telescope with a focal length of 2000mm has twice the power and half the field of view of a 1000mm telescope. Calculating Telescope Magnification. Calculating Magnification (power) To determine power in a telescope, divide the focal length of the telescope by the focal length of the eyepiece. By exchanging an eyepiece of one focal length for another, you can increase or decrease the power of the telescope. You will need to place the lens in front of the eyepiece. 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