-25-

is noticeably darker than that which can be obtained in a good Newtonian reflector.

Tube Design

     Because of the shape of the light path in the Yolo reflector, a tube of rectangular cross section will generally be found to be advantageous. Plywood is a satisfactory material for its construction. If the light-baffles too are made of plywood, they may be built integrally with the sides and thus serve as internal stiffeners for the tube. The muffle (that part of the baffle system extending forward of the secondary mirror) can be made of relatively light-weight material, circular in cross section, and detachable from the telescope tube, proper.

     In order to minimize the deleterious effects of possible convection currents in the air within the tube it is recommended that the inside surface of the tube should be no closer to the light path than one-half of the radius of the primary mirror. This means that the shorter dimension of the rectangular cross section of the inside of the tube should be no less than one and one-half times the aperture of the telescope.

Collimation

     Collimation of the Yolo reflector requires both mirrors to be tilted through the proper angles and the tilt-lines of both mirrors to be aligned accurately perpendicular to the principal plane of the instrument (the plane of the paper in Figures 1 and 5). When the warping harness is properly oriented, the two tension members ("pullers") which reach around to the front surface of