104 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Figs. 20, 21, 22, show the apparatus as arranged respectively for 

 episcopic and diascopic projections. The objective lens in figs. 20 and 

 21 is a ' Solar' of 400 mm. focus and an aperture of F : 4. In fig. 22 

 the rays reach the objective by diffuse reflection from the plate S^. 

 K appears to be a spherical reflector. The distance of the screen froni 

 the objective of the apparatus should be 5 m. in the centre with a ' play ' 

 of 2 m. With episcopic projection, however, good effects are not attain- 



FiG. 22. 



able beyond 6 m. The magnitude of the projected image at the middle 

 distance of 5 m. with an object 18 x 24 cm. is about 2 x 2'7 m. 



Fig. 22 shows the diascopic projection applied to small objects requiring 

 strong magnification. The focal length of the objective is 200 mm. A 

 lens, K, and a diapositive stage are placed in the ray-path as indicated. 

 The intensity of the ilhimination is thereby considerably increased. The 

 selection of lens and position of stage are such that the size and brightness 

 of the screen-image are the same as with the lower-power objective. 



