| 摘要 |
PURPOSE:To prevent the displacement of an image point owing to the deformation of a plastic lens occurring in humidity fluctuation by using a plastic index ring which expands and contracts by as much as the deviation on an object distance scale corresponding to the change in the combined focal length of the lens group of a focusing barrel when the humidity fluctuates. CONSTITUTION:The plastic index ring 10A made into a partly notched toric shape is fixed at the part near one end thereof to a fixing barrel 7 by means of a screw 15 and a pin 8 is implanted to the part near the other end. An index line 11 indicating the object distance scale 14 is marked near the other end. A long hole 9A which engages with the pin 8 and controls the turning of the focusing barrel 5A is bored to the barrel 5A from the point where the close up position of the scale 14 mates with the line 11 up to the point where the infinite position of the scale 14 mates with the line 11. The ring 10A is made of the plastic which expands and contracts by as much as the deviation on the scale 14 corresponding to the change in the combined focal length of the lens group of the cylinder 5A. |
