. The book of photography; practical, theoretical and applied. 516 THE BOOK OF PHOTOGRAPHY. those used for projection lanterns, 4^ , in front of which is placed a. two-lens system, the space between thelenses (7 in.) being filled with water. .The light emerges as a parallel beam l| in. indiameter. The lens sj-stem is fitted withvertical and horizontal screw adjustmentsand an iris diaphragm. Oil Lamps. The illuminants already consideredare excellent in every respect, but theyare somewhat expensive. For ordinaryphotomicrographic work with magnifica-tions up to about 400 diameters, the
. The book of photography; practical, theoretical and applied. 516 THE BOOK OF PHOTOGRAPHY. those used for projection lanterns, 4^ , in front of which is placed a. two-lens system, the space between thelenses (7 in.) being filled with water. .The light emerges as a parallel beam l| in. indiameter. The lens sj-stem is fitted withvertical and horizontal screw adjustmentsand an iris diaphragm. Oil Lamps. The illuminants already consideredare excellent in every respect, but theyare somewhat expensive. For ordinaryphotomicrographic work with magnifica-tions up to about 400 diameters, thehomelier paraffin lamp or incandescentgaslight will be found, when properly ap-plied, to be perfectly satisfactory. Theydo not give nearly the same intensity asthose already considered, and thereforethe time of exposure is more prolonged ;this, however, is only a slight drawbackin practice. With very high powers theyare, perhaps, inadmissible, because thelight is so faint on the screen that it isimpossible to focus with any lamp should be one with a broadwick, and this should be kept carefullytrimmed, the best result being obtainedwhen the edge of the fla
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