Magnification is the focal length of the primary mirror divided by the focal length of the eyepiece.<br /><br />The focal length of the primary is 1325 mm and the eyepiece that came with it ( according to this website ) is 25 mm so if you divide 1325 by 25 you get 53 power.<br /><br />In order to get 240X you divide 1325 mm by 240 which gives you the focal length of the eyepiece = 5.5 mm. <div class="Discussion_UserSignature"> </div>