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 > The usual procedure of measuring backlash is touching the
> direct and reflected image of the sun twice, on the same
> side (say Lover Limb), like you do when measuring
> the index correction, but by rotating the
> screw in two
> different directions, first clockwise then anticlockwise.
> The difference between your measurements is the backlash.

Alex

Think a power line might work as well or better than the the Sun's limb for
checking backlash. As was discussed on the list, our linear acuity seems to
be higher than one would expect.  I understand that parallax would come into
play for distances under 2-3 miles, but who cares if the measurement is off
the arc a bit?  What we care about is that the measurement is the same with
both clockwise and anti clockwise movement of the drum.  I used a tripod
mount with my Astra IIIB to do the above, and if there is any backlash
(which we know there will be, it is a matter of how much and is it
significant) it is less than my ability to align the wire consistently when
turning the drum in one direction--that being slightly less than 0.1'.

Bill

   

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