| 摘要 |
PROBLEM TO BE SOLVED: To provide a projection optical device that can suppress an increase in temperature of an optical system.SOLUTION: There is provided a projection optical device that includes a plurality of lenses that each have a flat surface formed on a part of its circumference, a substantially hollow cylindrical lens holder that holds the plurality of lenses, and a ventilation path that is formed by communicating gaps between the flat surfaces of the plurality of lenses and the lens holder.SELECTED DRAWING: Figure 6 |
