. The Ontario high school physics. l focus is outside the lenses. The Huygens eyepiece has two plano-convexlenses (Fig. 437), the one next the eye having afocal length J that of the other, and tlie distance between beingtwice the focal length of the shorter. This eyepiece is ordinarilyfound in microscopes, and it cannot be used as a simple microscope. 419. The Opera Glass. The opera glass has a convex lens forobjective and a concave lens for eyepiece (Fig. 438). Light from the object passes through theobjective 0, and would, ifallowed to do so, form a realimage J^-^Qy I^^t a concavelens -£, pl
. The Ontario high school physics. l focus is outside the lenses. The Huygens eyepiece has two plano-convexlenses (Fig. 437), the one next the eye having afocal length J that of the other, and tlie distance between beingtwice the focal length of the shorter. This eyepiece is ordinarilyfound in microscopes, and it cannot be used as a simple microscope. 419. The Opera Glass. The opera glass has a convex lens forobjective and a concave lens for eyepiece (Fig. 438). Light from the object passes through theobjective 0, and would, ifallowed to do so, form a realimage J^-^Qy I^^t a concavelens -£, placed in its way,diverges the rays so that onentering the eye they seemto come from /;</. This imageis erect and virtual. This instrument is alsoknown as Galileos was devised by this great man, and with it he discovered thefirst four satellites of Jupiter (1610), and also Saturns Ring. Ordinary opera or field-glasses consist of two Galilean telescopes,one for each eye. Such telescopes are simple in construction, of. FiQ. 438.—A section of the ordinary opera glass. 366 OPTICAL INSTRUMENTS convenient length and give an image right-side-up, hut their field ofview is not very great and they are not very serviceable for highmagnification. 420. Terrestrial Telescope. Wlien an ordinary telescope is tobe used for terrestrial purposes it is inconvenient to have the imageinverted, and to overcome this an erecting eyepiece is contains, in addition to the ordinary eyepioce, two lenses of equalfocal length placed so that they simply erect the image without other-wise altering it. Such an eyepiece also increases the field of view. 421. The Prism Binocular. In recent years there has comeinto use the prism binocular, which combines the compact form ofthe Galilean telescope with the wide field of view of the terrestrialtelescope. Its construction is illustrated in Figs. 439 and 440. The formershows the appearance of the instrument, while the latter shows theoptic
Size: 1997px × 1251px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
