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Make sure your darkfield
donut is in place over the
light port shown here.
If you have a variable iris as
shown here, remove the donut
and place the iris over the light
port instead. The iris assembly is
held in place by the raised ridge
that surrounds the light port.
When you put it in place there
will be a little bit of play in any
direction but it will be roughly
centered.
To move the iris assembly itself,
hold the outer portion of the
assembly with one hand, and
adjust the iris lever with the
other. An iris will give a little
more variability to the light as
opposed to the fixed aperture of
the donut.
Note that the 50x
oil objective has
an iris built into it
which rotates in
either direction.
When your 50x oil objective is in place over your
sample and your condenser is properly set to DF
mode with the light intensity turned UP, you will
need to adjust this objective iris to obtain the
image you desire. Note that different things in the
sample can be highlighted more or less dependent
on where the iris is set. To refine the image a bit
more, you might find that turning the camera Auto
Exposure off and manually adjusting the Exposure
Compensation, Time and Gain will do this.
