Step 4. When the above procedure is applied to all three corners you should elevate the
focus platform by turning the coarse focus gear anticlockwise (as seen from above).
Elevate it until the springs are almost fully compressed then lower it a few turns.
Your focus mechanism is now properly greased.
Adjusting the belt tension
The three eccentric belt tensioning devices are set to their minimum setting when the
scope is built and this is perfectly adequate because at that setting a new timing belt is
at its optimum tension level.
Too tight a tension and the stage will become difficult to move and XY hysteresis will be
exaggerated. Too loose a belt can cause exaggerated backlash as well as XY hysteresis.
So there is an optimum mid-range level of tension and this is the level of tension of a
new belt with the eccentric belt tensioning devices set to their minimum setting.
Over a period of several years it may become necessary to tighten the belt a little but do
not over-tension them. When adjusting belt tension note that each of the three arms of
the belt should be of equal tension.
The procedure, performed for each of the three belt tensioners, is as follows:
Step 1. Remove the optical tube and slide and keep them safely to one side.
Step 2. Slightly loosen the M4 screw that holds the tensioner in place but do not remove
the screw.
Step 3. With finger and thumb
rotate the upper part of the
belt tensioner device till you
achieve the desired degree of
tension. If it is too difficult to
rotate the device loosen the
screw a bit more and try
again.
Step 4. When the desired
tension position is reached,
re-tighten the M4 screw.
PUMA Foundation Scope
Page 34 of 40
User’s Manual v1.0