| 摘要 |
PURPOSE:To easily measure a focus distance, by decreasing the influence on a distance between principal points through reducing of an image formation magnification. CONSTITUTION:Through a lens 1 to be measured, an image, on a test chart 2, of a reference circle 3 with a diameter Dmm.phi is formed on a surface 5 of a pin hole 4 with a diameter dmm.phi, and while it is being observed by an enlarging mirror 6, an adjustment is conducted so that the image of the reference circle 3 coincides with the pin hole 4. In case a distance (l) between the test chart 2 and the surface of the pin hole 4 is enoughly longer compared with a focus distance f( b) of the lens 1 to be measured, a following formula is established. Since D and d in the formula of f=d/(D+d).l are constant, through the measurement of the l, the (f) is found. In this system, only the measurement of the l is enough, and this enables simplification of a measuring device. |
