The Galileoscope is a small mass-produced refractor telescope, designed with the intention of increasing public interest in astronomy and science. It was developed for the International Year of Astronomy 2009.
The Galileoscope uses a 1¼-inch focuser, giving the telescope a great deal of versatility, since this is the standard size for eyepieces used in most amateur- and some professional telescopes. This means the Galileoscope can be used with relatively cheap extra eyepieces to produce magnifications up to 100, or even 200 times (with a 5 mm in combination with the included 2x Barlow). According to telescope-theory however, a magnification of more than 125x would not be recommended for a scope this size because the aperture of 2" along with the focal length limits sharpness beyond this. Also the design of the slide-in/out focusing tube, without any gears or knobs, makes it near impossible to focus above the 125x limit.
It also utilizes achromat glass lenses in the objective-lens (the large 2" one in front), as well as in the eyepiece (4 lenses of two types of high quality plastic, known as a Plossl configuration) to prevent chromatic aberration, producing a clearer image. This is because single lenses, as are often used in cheap scopes, refract light of different colors in different angles (chromatic aberration). In practice this means all images will have blueish blurred edges on one side, reddish on the other, making the image very unclear. By using two types of glass for the two lenses this gets compensated to some degree, resulting in a sharper and clearer image. Depending on the configuration, 4, 6 or 8 lenses are used. The 4-lens configuration results in a telescope in some ways similar to Galileo's, with 17x magnification and a very small field of view. The 6-lens configuration provides 25x magnification, and the 8-lens configuration allows for 50x magnification. The user may easily switch between these configurations by changing the eyepiece.
See also 
- Review by Phil Plait, author of BadAstronomy.com
- Review on www.cloudynights.com was selected a gear of the year 2009
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