. The microscope : an introduction to microscopic methods and to histology. Microscopes. i6 MICROSCOPE AND ACCESSORIES [CH. I ''/. 26. Non-Adjustable or Unadjustable Objectives.—Objectives in which the lenses or lens systems are permanently fixed in their mounting so that their relative position always remains the same. Lower power objectives and those with homogenous immersion are mostly non-adjustable. For beginners and those unskilled in manipulating adjustable objectives ($ 27), non-adjusta- ble ones are more satisfactory, as the optician has put the lenses in such a position that the most
. The microscope : an introduction to microscopic methods and to histology. Microscopes. i6 MICROSCOPE AND ACCESSORIES [CH. I ''/. 26. Non-Adjustable or Unadjustable Objectives.—Objectives in which the lenses or lens systems are permanently fixed in their mounting so that their relative position always remains the same. Lower power objectives and those with homogenous immersion are mostly non-adjustable. For beginners and those unskilled in manipulating adjustable objectives ($ 27), non-adjusta- ble ones are more satisfactory, as the optician has put the lenses in such a position that the most satisfactory results may be obtained when the proper thickness of cover-glass and tube-length are employed (See table of tube- length and thickness of cover-glass below (\ 34). j! 27. Adjustable Objectives.—An adjustable objective is one in which the distance between the systems of lenses (usually the front and the back systems) may be changed by the observer at pleasure. The object of this adjustment is to correct or compensate for the displacement of the rays of light produced by the mounting medium and the cover-glass after the rays have left the object. It is also to compensate for variations in '' tube-length". See \ 32. As the displacement of the rays by the cover-glass is the most con- stant and important, these objectives are usually designated as having cover- glass adjustment or correction. (Fig. 28. See also practical work with adjustable objectives, Ch. II.) \ 28 . Parachromatic, Pantachromatic and Semi-apochromatic Objec- tives.—These are trade names for objectives, most of them containing one or more lenses of the new glass [\ 25). They are said to approximate much more closely to the apochromatics than to the ordinary objectives. § 29. Variable Objective.—This is a low power objective of 36 to 26 mm. equivalent focus, depending upon the position of the combinations. By means of a screw collar the combinations may be separated, diminishing the power
Size: 1252px × 1996px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicroscopes, bookyear
