IMAGE TRANSMISSION SYSTEM 467 



which passes across the image and is placed at the height at which the 

 user's eyes should appear. 



The height of the observer's eyes is an indication of the position 

 which should be taken by the large magnifying lens L, and the operator, 

 after having properly placed the scanning beam, reads the scale on the 

 variable angle prism dial, and then sets the magnifying lens by turning 

 its controlling knob to the same number. When both adjustments 

 are complete, the person in the booth will not only be properly scanned 

 but will be in the best position to see the image. 



In order to monitor the incoming image, an optical arrangement is 

 adopted by means of which light from the water-cooled neon lamp is 

 taken off at the side and reflected through the disc and thence reflected 

 again, as shown in Fig. 14 (top of bottom disc), through a second, 

 lower, observing hole on the side of the motor cabinet. Because of 

 the small area of the side view of the neon lamp, a lens system is 

 inserted which focusses the image of the lamp at the place to be 

 occupied by the pupil of the operator's eye. When the eye is properly 

 placed, the whole of the lens area is seen filled with light and exhibits 

 the incoming image. 



In addition to the monitoring means just described, an additional 

 view of the incoming image is provided by means of a 45° mirror 

 which is carried on the back of a movable shutter which is shown 

 at S in Fig, 4. This shutter carries an illuminated sign on the side 

 turned to the user with the inscription "Watch this space for 

 television image." The shutter with its sign covers the image until 

 the adjustments just described are made, when it is dropped out of 

 sight. While it is in place, the operator is provided with an additional 

 monitoring image reflected from the 45" mirror. This view is, of 

 course, in every respect identical with that which the user sees. 



The function of the incoming monitoring system is primarily to 

 enable the operator to set the electrical controls to give the proper 

 quality of image. He also has another task which is that of properly 

 framing the image. This he can do by turning the framing handle, 

 which is described elsewhere, while watching the image from the 45° 

 mirror. This framing operation is preferably performed not on a 

 person sitting in the booth but upon some suitable object such as a 

 mirror located upon the rear door of the booth. In order to make 

 this framing adjustment, the operators at the two terminals set their 

 scanning beam dials to predetermined positions such that the scan- 

 ning beams place the framing mirrors at the lower edge of the scanning 

 rectangles, the phases of the incoming discs are then shifted until the 

 images of the mirrors are seen properly located in the incoming mon- 

 itors. 



