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The positive groups, considered separate from the first negative group, combine to have long focal length, and form a positive lens. That allows the design to take advantage of the many good qualities of low power lenses. In effect, a Nagler is a superior version of a Barlow lens combined with a long focal length eyepiece.
Using an example of an amateur telescope such as a Newtonian telescope with an aperture of 130 mm (5") and focal length of 650 mm (25.5 inches), one uses an eyepiece with a focal length of 8 mm and apparent FOV of 52°.
A Boeing 747-400 aircraft at 11,000 metres, photographed from the ground using a 1,200 mm telescope and a 2x Barlow lens.. In its astronomical use, a Barlow lens may be placed immediately before an eyepiece to effectively decrease the eyepiece's focal length by the amount of the Barlow's divergence. [1]
Engraved illustration of a 46 m (150 ft) focal length Keplerian astronomical refracting telescope built by Johannes Hevelius. [11] The Keplerian telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design. [12] It uses a convex lens as the eyepiece instead of Galileo's concave one.
Camera lenses use a wide variety of designs because of the need to balance and trade off different requirements: angle of view (i.e. focal length in relation to the film or sensor size), maximum aperture, resolution, distortion, color correction, back focal distance, and cost. Celor lens; Chevalier lens; Cooke Triplet; Double-Gauss lens ...
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 2× Barlow lens). However, a magnification of more than 125× would not be recommended for a scope this size because its focal ratio limits sharpness beyond this.
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3579 S High St, Columbus, OH · Directions · (614) 409-0683