PURPOSE: To render optical axis corrections following the change of an outside air temperature unnecessary by forming an optical cylinder wherein the thermal expansion coefficient of carbon fiber being substantially minus in the parallel direction with the cylindrical axis direction and the thermal expansion coefficient as CFRP in the cylindrical axis direction is in a specific range.
CONSTITUTION: Inasmuch as the thermal expansion coefficient a carbon fiber reinforced plastic(CFRP) layer is markedly different in the fiber axis direction and the right angle direction with the fiber axis, in the case of employing minus carbon fiber in its thermal expansion coefficient, the thermal expansion coefficient α being in the right angle direction with the carbon fiber direction in the CFRP layer 1 is made 30-40×10-6/°C and the thermal expansion coefficient αin the carbon fiber direction in the CFRP layer 2 is made -1×10-6/°C, thereby forming an optical cylinder made of CFRP. Concretely, prepreg obtained such that a predetermined quantity of thermosetting resin is impregnated into carbon fiber is cut into an appropriate direction and then wound round a cylindrical mold to thereby obtain a CFRP optical cylinder through heat pressing and lamination molding. Besides, the thermal conductivity in the thickness direction of the CFRP optical cylinder is preferable to be 0.1W/m.K or lower.
MOROHASHI KAZUO
TAKAHASHI HIDETOSHI
