112. =Larger Projection Apparatus with Camera= for plates 9×12, 13×18, 18×24 and 24×30 cm =56.--= The following Objectives of 24, 35, 42 and 64 mm focal distance respectively may be used in connection with this apparatus for photographic purposes. 113. } { of 24 mm focal distance =18.--= 114. } =Photographic Objectives { " 35 " " " =18.--= 115. } with Iris diaphragms= { " 42 " " " =18.--= 116. } { " 64 " " " =20.--= The following table shows the size of the preparation which may be resolved by each one of these objectives and the magnification with the smaller and with the larger Edinger Projection Apparatus. -------------+----------------+-------------------------------------- | Size of the | Magnification Objective | Preparation | | Focal length | Maximum | Smaller Apparatus | Larger Apparatus -------------+----------------+--------------------+----------------- 24 mm | 8 mm | 7-15 diam. | 13-25 diam. 35 mm | 15 mm | 5-12 diam. | 10-20 diam. 42 mm | 20 mm | 3-9 diam. | 6-13 diam. 64 mm | 35 mm | 2-4 diam. | 3-8 diam. -------------+----------------+--------------------+----------------- The time required for exposure in photographing with this apparatus is from 5 to 20 seconds according to the magnification and character of the specimen. The following figure shows a further use for the Objective of 64 mm focal distance in connection with the photomicrographic apparatus (page 82). [Illustration: Photo-micrographic apparatus No. 105 with small stand No. 106.] =Large Projection Apparatus.= In this projection apparatus an electric projection lamp is made use of, the lamp being available for electric currents of 20 Ampères and about 48 Volts. To regulate the current a rheostat is necessary. When using constant current the carbons should stand at an angle in order to utilize to best advantage the stronger light of the positive (upper) carbon. For spectroscopic projections the carbons of the lamp have to be in vertical position. Connected with the lamp is a triple condenser of 150 mm aperture. The latter should be protected from the heat-rays by a large mica-plate which is furnished with the apparatus. Various devices permit very accurate adjustment of the lamp and condenser. For example, two thumb-screws control the position of the carbons of the lamp so that the luminous point may be readily brought into the exact optical axis of the condenser. Again, the two inner lenses of the condenser are moveable and are controlled by two knobs conveniently situated as shown in the illustration.