Aperture size can be used to make other calculations when used with correct formulas.
Aperture on a telescope is the size of the primary lens (called the objective lens) at the front end of the tube body, in the case of a refractor telescope, or large reflective mirror at the rear end of the tube body on a reflector telescope. The aperture of the mirror or lens itself can be measured in inches diameter and then converted to millimeters in diameter. The aperture diameter size, in millimeters, can then be used to find theoretical minimum and maximum magnifications and focal length of the telescope. Focal length is needed when buying viewing lenses.
Instructions
1. Measure the diameter of the objective lens or opening at the front of the telescope tube body. If the telescope is a refractor, it will have a thick glass objective lens at the front. To measure the aperture for a refractor, use a measuring ruler to measure from the edge of one side of the lens to the edge of the other size of the lens. For a reflector, measure from one side of the inside lip of the opening at the front of the telescope, to the inside of the lip on the other side of the opening. If the ruler doesn't have a measurement scale in millimeters, convert inches to millimeters by multiplying the number of inches times 25.4 for the total number of millimeters. This is the total diameter, in millimeters, for the aperture of your telescope.
2. Calculate the theoretical minimum and maximum magnifications the aperture provides, using the calculated aperture width in diameter, by using that diameter in the following formulas. Minimum power = D/6; Maximum power = D/1.58. "D" stands for "Diameter" of the aperture, in millimeters. If the telescope aperture is 8 inches, it has 203.2 millimeters. The minimum power of this aperture is 203.2 divided by 6, for a total of 33.866 magnitude. The maximum power of this aperture is 203.2 divided by 1.58, for a total of 128.607 magnitude.
3. Determine focal length of the telescope using the aperture diameter, in millimeters, and the advertised focal ratio of the telescope. If the telescope you purchased is sold with the focal ratio advertised as f/5, for example, and continuing with the knowledge that the aperture diameter of the telescope is 203.2 millimeters, multiply 203.2 times 5, which then results in a focal length calculation of 1,016 millimeters focal length.
Tags: focal length, aperture diameter, objective lens, tube body, aperture divided, aperture divided total, diameter millimeters
