| 摘要 |
PURPOSE:To smooth focusing function and to prevent the deterioration in optical performance, by providing oil wells in the trough of a screw. CONSTITUTION:Focusing is accomplished by the relative rotation of a male helicoid 4 and a female helicoid 5, and both helicoids are slid by the intermeshing part 9 of the thread ridge 1 and trough 2 of helicoids 8. The helicoids 8 are intermeshed with each other with high accuracy for the purpose of preventing the deviation of optical paths of lens group L1-L3. The lubricating effect for smoothing the sliding movement of the part 9 is attained by the grease which is supplied gradually from oil wells 3. Since the wells 3 are formed in each trough 2 of the helicoids 8, the lubricating oil is supplied naturally to the part 9. The wells 3 function as oil wells even if the wells 3 are formed to a circular, elliptical or square shape or to the shape having the trough 2 deeper than the ordinary trough 2. |
