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The 10 inch mirror in its
cell.
Judging the
centre by eye to within a millimetre or two is not easy. |
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A steady hand is needed for
this - no finger prints or scratches on the mirror!
I used a paper circle from a pack of
writeable CDs. It had a neat hole in the centre of just the right
size.
The paper disc
was lightly lowered onto the mirror and measurements made from the edge of the
paper to the edge of the mirror. The paper was gently adjusted by nudging it
with a soft artist's paint brush.
When the paper was centred a small metal weight was very
carefully lowered to act as a paper weight.
Measurements were repeated in case
the paper had moved.
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Then the reinforcement circle
was held with tweezers and placed in the centre.
A final check showed that the edge
of the circle was 12.2 mm from the mirror edge in all
directions.
Success!
The laser can now be directed to land on the dead centre of the
mirror.
Note:
It would be easier to cut out a 10 inch diameter paper circle that fitted the
mirror and then make a small hole in its centre... but I didn't have a large
piece of paper to hand.
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The secondary mirror is adjusted to make the laser beam land
exactly in the centre of the primary mirror.
Collimation is completed by
adjusting the primary mirror to return the laser beam back to the
collimator.
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