. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ment hereafter described, withgood results. Generally the foci supplied rangefrom 2| and 1\ inches, to 2 inches and 1 objectives slide into the rack-front, andthus roughly adjust focus, precisely as thelantern-front recommended on p. 33, the higherpower having of course to be pushed farther into the tube. With the single-stage form of attachment, all that can bedone is to roughly focus the object on the screen, and thendraw back the lime-tray a little, and adjust it to and fro in
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ment hereafter described, withgood results. Generally the foci supplied rangefrom 2| and 1\ inches, to 2 inches and 1 objectives slide into the rack-front, andthus roughly adjust focus, precisely as thelantern-front recommended on p. 33, the higherpower having of course to be pushed farther into the tube. With the single-stage form of attachment, all that can bedone is to roughly focus the object on the screen, and thendraw back the lime-tray a little, and adjust it to and fro in thelantern, till the object is most brilliantly illuminated, whichwill be when it is just at the focus of the cone of rays from thecondensers. This will also, for reasons already pointed out,be the position of best definition. The object may, however,be rather too large to be covered by such a focus, and if so theexhibitor must alter the focus a little to get the best result hecan. These results, with a good operator and a good jet, maybe very fair up to the limits of the powers supplied, which are. Fig. 79 150 OPTICAL PROJECTION better as a rule for this class of work than achromatics. Suchan object, for instance, as the head and tongue of a bee, can beshown with the higher of the two powers very fairly, as regardsthe general structure. There is great heat at the focus of the cone of rays, andthe microscopic attachment should therefore never be used formore than a few seconds, without a large glass trough, filledwith saturated and filtered solution of alum, being first placedin the ordinary slide-stage of the lantern. For exhibiting ordinary microscopic slides a wooden frameis used, somewhat similar to the ordinary frames of lanternslides. It is made to fit the stage of the attachment outside, andthe ordinary 3x1 inch micro-slides inside. This frame hasa movable end, by which the slides can be inserted in it asrequired. With the double-stage instrument as shown in the figure,m
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
