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5-2-2. Optical Axis Check
Checking Procedure
1. Adjust the optical axis while observing the microscope until the
chart image can be seen in the center.
2. Perform steps (1) to (6) and check that the AS and CB values are
within specifications.
AS (Astigmatism):
The phenomenon where the flare on the ring chart appears in a
cruciform shape with the ring chart in the sharpest focus. (Fig. a)
(1) Turn the focusing knob until the flare becomes minimum
between two approximately opposite points on the ring
chart edge (as shown with the arrows in Fig. b), and then
read the dial gauge value. <A>
(2) Turn the focusing knob until the fl are becomes minimum
between two points with the phase of the fl are rotated by 90
degrees from the above step (1) condition (as shown with
two arrows in Fig. c), and then read the dial gauge value.
<B>
(3) Calculate the AS value (absolute difference between <A>
and <B>) and check that it is within the specifi cation.
AS value = <A> − <B>
AS
(Fig. a)
CB (Center Blur):
The phenomenon where the flare on the ring chart trails in one
direction with the ring chart in the sharpest focus. (Fig. d)
(4) Turn the focusing knob until the ring chart edge in the direc-
tion of the maximum fl are is in the sharpest focus (as shown
with the arrow in Fig. e), and then read the dial gauge value.
<C>
(5) Turn the focusing knob until the ring chart edge, opposite
180 degrees from the above step (4) condition (as shown
with the arrow in Fig. f) is in focus, and then read the dial
gauge value. <D>
(6) Calculate the CB value (absolute difference between <C>
and <D>) and check that it is within the specifi cation.
CB value = <C> − <D>
CB
(Fig. d)
Specifi cation (Reference):
AS (Astigmatism)
0.06 mm or less
CB (Center Blur)
0.09 mm or less
3. If the specifications of AS and CB are not satisfied, replace the
2-3 Group Block Assy or 4 Group Block Assy.
(1)
(2)
(1)
(Fig. b)
(Fig. c)
(5)
(4)
(Fig. e)
(Fig. f)
(2)
5-10
SELP18110G
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