2-12
2 PREPARATION FOR MEASUREMENT
2.6 FOCUSSING AND TARGET SIGHTING
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When sighting the target, strong light shining directly into the objective lens may cause the
instrument to malfunction. Protect the objective lens from direct light by attaching the lens hood.
Observe to the same point of the reticle when the telescope face is changed.
PROCEDURE
1
Look through the telescope eyepiece at a bright and
featureless background.
Turn the eyepiece screw clockwise, then counterclockwise
little by little until just before the reticle image becomes
focussed.
Using these procedures, frequent reticle refocussing is not
necessary since your eye is focussed at infinity.
2
Loosen the vertical and horizontal clamps, then use the
sighting collimator to bring the target into the field of view.
Tighten both clamps.
3
Turn the telescope focussing ring to focus on the target.
Turn the vertical and horizontal fine motion screws to align
the target with the reticle.
The last adjustment of each fine motion screw should be in
the clockwise direction.
4
Readjust the focus with the focussing ring until there is no
parallax between the target image and the reticle.
Eliminating parallax
This is the relative displacement of the target image with respect to the reticle when the observer’s
head is moved slightly before the eyepiece.
Parallax will introduce reading errors and must be removed before observations are taken. Parallax
can be removed by refocussing the reticle.
