Because the moving parts of the telescope weigh over 25,000 lbs, it is
important to know that the telescope is properly balanced before
unclamping it. Figures 1 and 2 show the typical positions for the
weights when the eyepiece or bifilar micrometer is used. A different
weight arrangement is necessary when using the automatic plate camera
or other instrument (note that no instruments other than the eyepiece
and bifilar micrometer are currently supported, though observers may
apply to provide their own instrument, at which point the observatory
staff will assist in properly balancing the telescope for the provided
instrument). Depending on the mass of the instrument, the main
counterweights (Figure 3) may need to be adjusted as well. Observers
should never adjust balance themselves and if the balance of the
telescope is in question they should contact a telescope technician or
Observers are never allowed to change the instrument themselves. However, we include the following for completeness. When changing instruments it is important to anchor the telescope so that it will not move when unbalanced. This is done by opening the hatch below the telescope's normal stow position and hooking the cable to the ring (Figure 4). This cable is fastened to the floor and will prevent the telescope from moving when unbalanced. One must have this cable attached before removing an instrument (an observer decades ago was gravely injured when he did not remember to affix the cable, removed the instrument, and the telescope became dangerously unbalanced. The telescope was also slightly damaged in this instance). Additionally, one must be absolutely certain that the telescope is balanced properly before removing the safety cable to prevent injury or damage to the telescope. When done with the safety cable, stow the cable in its compartment in the floor and be sure to replace the hatch cover so that is it flush with the floor.
Extra weights are stored in a cart (Figure 5) on the east side of the telescope pier. Note that the RA dial adjuster is also stored in the weight cart, so be sure not to damage it accidentally with the weights. Also, the weights contain lead, so wash one's hands after handling them.
Figure 1: Left counterweights.