152 



Projection Apparatus and Accessories. 



For Diapositives 7x7 cm free aperture a condenser 102 mm diameter is necessary 



8.5X10 ,, 122 



9X12 ,, ., 152 



The following distances between Projector and Screen are recommended assuming a magni- 

 fication of from x 30 to X 40: 



With 102 mm Condenser; distance about 4 6 m 



122 ., 68 



1 K9 Q 1 1 



.. _LO*J .. <* * O -LJ- .. 



The sizes of image given in the Table are obtained at the distances of objective from screen 

 given with the various sizes of condensers and objectives, and with free aperture of diapositiA^e 7x7 cm. 



For larger photographs the distances between objective and screen should be proportio- 

 nately less if the resultant image on the screen is to be of the same size. The larger condensers necessi- 

 tate a higher candle-power. For lanterns having larger condensers, therefore, arc lamps for higher 

 currents should be selected. 



Instead of employing the simple achromatic projection objective usually supplied with the 

 projectors, a Projection Anastigmat, a Steinheil Group Antiplanet, or a Voigtlander Heliar should be 

 selected if it be desired that the resultant images should be equally as brilliant at the edges as in the 

 centre. If the experimenter has at his disposal a source of light of considerable brilliancy, obtained 

 from the arc lamp, thereby rendering a considerable degree of magnification possible, the magnification 

 should not be carried too far, as the result is too weakly illuminated and blunt images. A magnifi- 

 cation of 30 40 times is most suitable. 



Construction and Selection of Projection Lanterns. 



General. The illustration appended shows a section through a projection lantern with arc lamp 

 corresponding to our Model B type, with aluminium housing and with auto regulating arc lamp sus- 

 pended vertically. The light pencil from the arc lamp is collected on the condenser K and rendered 

 convergent. The diapositives or apparatus, of which certain parts are to be observed in an obj ective manner, 

 are placed or erected in front of the condenser, by which they are thoroughly and brilliantly illuminated, 

 and the light transmitted is projected from the objective O on to the screen with proportionate magni- 

 fication. The lantern can be used for the most diverse purposes of illumination without the optical 

 bench B (which can easily be detached by removing two nuts M) and without the objective O; in this 

 case it replaces the heliostat, excepting in experiments with the solar spectrum. C shows a slider con- 

 taining the diapositive change frame. 



The projection apparatus constructed by us are the following types: 



1. Model A, School Type Projector, simply but reliably constructed, having optical bench and 

 being arranged so as to work with any method of illumination, and capable of being employed for all 

 kinds of projection by using the corresponding auxiliary apparatus. Fig. 50,735. 



