How Sport Optics Work


Not everyone thinks of a binocular as two parallel telescopes, but that's exactly what they are.  Neglecting the prisms which turn the image right-side up, the binocular (singular, not plural) consists of an objective to form an image just like a camera lens, and a magnifier to view the image directly.  The magnifier is called an eyepiece, or ocular.

The ratio of the focal length of the objective to the focal length of the eyepiece gives the magnification, or power of the binocular.  For much, much more detailed info on the binocular, please follow this link.


What does a telescope have that half a binocular doesn't?  For one thing, flexibility, that is, interchangeable eyepieces with different focal lengths so that almost any power can be obtained.  And brightness, as most telescopes have 3, 4, 5, 6, 8, 10 or more inches aperture, so that there's ample exit pupil for bright images at higher powers.  And finally, resolution, since higher power generally shows greater detail. 

Detail is limited by the quality of manufacture, aperture, and turbulence in the atmosphere.  In practice, about 50 power per inch of aperture is the upper practical limit.  For much, much more detailed info on the telescope, please follow this link.


A spotting scope is a small telescope that has been modified for use by day.  A spotting scope differs from an astronomical telescope in several important ways.  First, a spotting scope always produces an upright image whereas a telescope used in astronomy may produce a reversed image or even an upside down image.  Second, a spotting scope is much smaller in size than an astronomical telescope, mainly for the sake of portability.  

Third, a spotting scope is a lower magnification instrument than a telescope, since the atmosphere by day does not allow the high magnifications used in astronomy.  Fourth, a spotting scope is mounted on an ordinary photo tripod, but a telescope for astronomy requires a specialized mount, often unsuitable for daytime use.  Lastly, many, if not most, spotting scopes are waterproof and fogproof - a rare feature in an astronomical telescope.  For much, much more detailed info on the spotting scope, please follow this link.