Also the relative time of presentation of a "band may he changed as in 
fig. 4h. 
Now all fields with spectral characteristics like the testsfield are 
optimal flicker presented to the eye of the interpreter. Viz. when 
increasing the cycle frequency of presentation the perceived flickering of 
all other fields is attenuated more than that of the test class. As this 
flicker threshold detection depends on cycle frequency and on variation 
between bands, the flicker threshold is not a unique criterium. But by the 
’’subtraction” of superimposed classes, subclasses with lower initial 
variation between bands, may still be separated from classes with different 
spectral characteristics but greater variation. 
HARDWARE DESIGN OP THE CAROUSSEL 
Design considerations: up to 8 spectral band transparencies 
60 mm x 60 mm projected on a nearly horizontal table top screen of 
180 mm x 180 mm. Only one central projection lamp, 8 radial symmetric 
optical trains, one projection lens with pathfolding mirrors. In each of 
the 8 separate optical trains; condensor systems, a callibrated grey wedge, 
removable colour filter, an independent electronically controlled shutter 
with 5 ms response time, a transparency holder with 3 motors for remote 
registration (x, y and k). Moreover the caroussel was designed on 
ergonomic principles to facilitate easy, non stressing, non tiring 
operation. The opto-mechanical part of the caroussel was designed, built 
and callibrated by a TPD (Technisch Physische Dienst) team. The electronic 
control for the shutter drivers (loudspeakers with vanes for ray- 
path cutting) was designed and built by the ITC physics department 
The opening and closing times for each shutter can be set with a thumb 
wheel to one from 0 to 99 units within one repetition cycle of presentation. 
The repetition time/frequency can be continuously changed by.hand. 
It is also possible to have the cycle repeating in less then 99 units e.g. 
after 79 time units.