By Stephen F Tonkin

ISBN-10: 1852330007

ISBN-13: 9781852330002

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Most experts however, agree that if the secondary mirror's minor axis is less than 15% of the diameter of the primary mirror then the harmful effects all but vanish. 2). Since a secondary mirror of some size is necessary for the telescope to even work, the best one can do is keep this obstruction, and the resulting harm, to a minimum. So how big should the secondary be? This too is the subject of great debate, and there really is no single "correct" answer. A good place to start is to figure out the size of a secondary that will just barely do the job.

25 in (6 mm) plywood, cut to the diagonal's outline, attaches with a screw and epoxy to the diagonally cut stalk. I drilled holes 120° apart inside the edges of the plywood, which has a polyurethane varnish coating. I squeezed silicone glue into the holes, and used pennies as spacers, and with a vice levelling the plywood, I lowered the diagonal, back side down, onto the silicone blobs. After a 24-hour curing period, I completed the installation of the diagonal and twovane spider assembly. 5 in (38 mm) aluminium angle to the focuser board on opposite sides to allow attachment of the two-vane spider assembly.

Screen door handles attached to the box sides permit easy handling and transport. A large corrugated cardboard pizza box, reinforced with foam board and fibreglass tape, protects and stores the mirror when not in use. 4, overleaf) using /2 in thick birch plywood, 1/8 in thick door skin and foam core. 4 The mirror box and rocker assembly. materials, Steven Overholt's book, Lightweight Giants, detailed a "low-tech" approach to composite manufacture utilising thin wooden door skin, carpenter's glue and Styrofoam building panels.

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