It is
possible to perform shading measurements on illuminator (LG2, LE6)
without any chart. But then lightning conditions are different to other
measurements with test transparencies. By using a test transparency the
light intensity of an illuminator changes.
This is caused by two superimposed factors
a) the filter effect of the film and glass (25% light absorption) and
b) the light remission of the transparency ack in the illuminator
While
factor a) is predominat with th LG2, the remission factor b) is
predominant with the lightning sphere LE6, i.e. the light intensity
rises significantly when a test chart is inserted. To carry out shading
measurement under the same lighting condition as other measurements the
use of the YE0178 is essential.
Definition of white shading or white level uniformity
Determination
of maximum white level variations in various areas of the picture, when
the camera is directed at an evenly illuminated test chart.