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. For example, a telescope with a focal length of 2000mm has twice the power and half the field of view of a 1000mm telescope. Our Overall #1 Rated Pick If you're looking for the best telescopes with excellent magnification that is affordable, easy to use for beginners, and has a great build quality, our top pick is the Meade Instruments – Polaris 90mm. Several factors affect the magnification of the telescope then, you can decide what should be the magnification of an ideal telescope for you. Magnification or power of a telescope is its ability to enlarge small objects from far distances. The magnification of a telescope and eyepiece is very simple to calculate. It does so by magnifying the image. An 8″ telescope has a minimum of 29x, and a 14″ telescope has a minimum of 50x. For example, if you use a telescope of 1000mm focal length with a 25mm eyepiece, the magnification would be 40x (1000mm ק 25 = 40). Magnification = Telescope focal length ק Eyepiece focal length. For example, a 4″ telescope has a minimum magnification of 14x. The result is that the image being observed is magnified. By exchanging an eyepiece of one focal length for another, you can increase or decrease the power of the telescope. With most professional telescopes, you will have to remove it every now and then in order to recalibrate. An additional thing you can do to expand the magnification of your telescope further, is to add a Barlow Lens. Increasing Telescope Magnification with a Barlow Lens. The magnification is the telescope focal length divided by the eyepiece focal length, in millimeters. Below the minimum magnification, the effect is to stop down the aperture. 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. This is 2mm larger than the typical dark-adapted human eye. So, a 14″ telescope used at 40x gives an exit pupil of 9mm. A Barlow lens spreads light out and increases a telescope’s focal length. This feature can be manipulated using different combinations of objective and eyepiece lens. You will need to place the lens in front of the eyepiece. In general, when the magnification of scope increases, the image brightness, and field of view (FOV) decreases. 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 magnification of a telescope is measured by dividing the diameter of the objective lens over the focal distance of the telescope. Calculating Magnification (power) To determine power in a telescope, divide the focal length of the telescope by the focal length of the eyepiece. 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. Telescope Magnification Formula. Calculating Telescope Magnification. The role of the lens is to reflect, while the role of the eyepiece is to give a closer and more detailed look.