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2) Brightness adjustment with ND filters
Filters for controlling light quantity are called ND filters.
ND filters having larger
numbers provide less transmission and therefore darker images.
For color film,
light quantity is controlled with ND filters, not by varying the lamp voltage.
This is because the change of lamp voltage leads to the change of color
temperature which greatly effects the photomicrography.
ND filters are to be attached to the filter slider at the diascopic illumination unit.
(See page 43.)
ND2
: Reduces light quantity to 1/2.
(Approx. 50% transmissivity)
ND1 6: Reduces light quantity to 1/16.
(Approx. 6% transmissivity)
Figure 4-3
18
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