The concrete formwork for the foundation of the observatory's cylindrical base is now complete. With both internal and external bracing (only internal bracing is shown in the photo to the right), this is a stiff formwork that is very easy to construct.
Spacers
Wooden spacing rods are fastened with screws between the two plywood rings. These spacers are 25 cm long, forming a concrete ring that is the same width as the cinder blocks. The spacers will be removed when the form is anchored with concrete blocks around its perimeter.
Centering
Two long poles, each three meters long, intersect at the center of curvature. They serve two functions: 1) They center the formwork on the rotational axis of the dome, and 2) they ensure that the structure is circular instead of ellipsoidal.
The baseplate of the telescope mount is offset 9 cm north of the dome's rotational axis. At the intersection of the two centering poles is a long wood screw which extends down to the concrete base, resting in a cavity drilled at the axis of the dome. This keeps the formwork centered on the telescope pier with a very small margin of error. Accurate centering is important because the four meter enclosure leaves very little clearance between the prime focus camera and dome.
