User manual CELESTRON FIRSTSCOPE 90EQ Instruction Manual

[. . . ] FIRSTSCOPE 70 & 90 EQ TELESCOPE INSTRUCTION MANUAL Firstscope 70 EQ - #21076 Firstscope 90 EQ - #21085 17 1 2 16 15 3 14 4 5 13 6 12 7 11 8 10 9 Firstscope Refractor 70mm EQ shown 2 IDENTIFYING PARTS OF YOUR FIRSTSCOPE 1. Objective Lens INTRODUCTION Thank you for purchasing this Celestron Refractor Telescope. This telescope is a precision scientific instrument. With it you will enjoy numerous objects in the sky--planets, nebulae, star clusters, galaxies and other astronomical objects. [. . . ] Observers in the northern hemisphere should use the upper set of numbers while southern observers should use the lower set of numbers. Remember in the northern hemisphere, the right ascension should decrease as the telescope is moved towards the west. The right ascension setting circle does not move as the telescope moves in right ascension and thus it must by aligned each time you want to use it to find a new object. However, you do not need to use a bright star each time but you can use the object you are currently observing. Now, using a star chart or atlas you can find numerous objects. First move the telescope in declination to the correct declination coordinate. Then move the telescope in right ascension until the indicator points to the correct coordinate. After moving the telescope to the correct celestial coordinates, look through the lower power eyepiece to see if you have located the object you wish to view. If the object is not visible in the eyepiece, gradually pan the telescope, using the right ascension and declination cables, until the object is visible. Always start by using your lowest power eyepiece (20mm) then switching to higher power once you have found the desired object. 2. 6. 11 MAGNIFICATION (POWER) The magnification (or power) of a telescope is variable depending upon the focal length of the eyepiece being used along with the focal length of the telescope. In equation format, the formula looks like this: Magnification = FL(telescope) FL( eyepiece) To determine the magnification using the standard 20mm eyepiece, simply divide the focal length of your telescope by the focal length of the eyepiece (20mm). For example, dividing the focal length of the Firstscope 90 (1000mm) by 20mm yields a magnification of 50 power. Magnification through the telescope has its limits. These limits are determined by the laws of optics and the nature of the human eye. The maximum usable power is equal to 60 times the aperture of the telescope (in inches). For example, using the 70mm model (2. 8") then your maximum useful power is 168x (2. 8" x 60). You can create power higher than this limit but the images will be dark and blurred with poor contrast. The maximum power is used only under ideal conditions which are not common. Most of your viewing will be done in the range of 25x to 120x. Higher powers are used mainly for lunar and planetary observing under ideal seeing conditions. Determining Field of View Determining the field of view is important if you want to get an idea of the angular size of the object you are observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by the magnification. [. . . ] As a condition to the obligation of Celestron to repair or replace such product, the product must be returned to Celestron together with proof-of-purchase satisfactory to Celestron. The Proper Return Authorization Number must be obtained from Celestron in advance of return. Call Celestron at (310) 3289560 to receive the number to be displayed on the outside of your shipping container. All returns must be accompanied by a written statement setting forth the name, address, and daytime telephone number of the owner, together with a brief description of any claimed defects. [. . . ]