JPS6331764B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention provides a macro lens with a telephoto focal length used in a photographic camera, which has high lens performance at all photographic magnifications from infinity to 1x, and in all conditions from wide open to closed aperture. This invention relates to a focusing method for a telephoto macro lens in which the aperture is moved during focusing in order to maintain the following. Prior art and its problems In conventional telephoto macro lenses, the aperture is fixed integrally with the fixed lens group (rear group).
When focusing, there is a problem that if you stop the lens at a high magnification (i.e. close distance side), only the marginal (peripheral) luminous flux will remain, and the performance at the periphery of the screen will deteriorate when the lens is stopped down. Ta. In a macro lens having a standard or semi-telephoto focal length, the angle of view is large, so the aperture must be included in a movable lens group (master group) and cannot be moved independently. In addition, when zooming rather than focusing, a so-called 2-group zoom lens or a modified version of the 3-group or 4-group zoom lens, in which all of the groups move, is used to correct flare that accompanies zooming, for example. It is conventionally known that the aperture moves, but this movement of the aperture has nothing to do with the aperture effect (lens performance), and the aperture does not move during focusing with a zoom lens. Purpose The present invention was made to solve the problems of the above-mentioned telephoto macro lens.
In telephoto macro lenses for photographic cameras that consist of a negative lens group, the aperture is moved independently during focusing in order to take into consideration the aperture placement and improve the aperture effect, that is, the lens performance when stopped down. The present invention aims to provide a focusing method for a telephoto macro lens as described above. Structure of the Invention The present invention comprises, from the object side, a first lens group having a positive focal length and a second lens group having a negative focal length, and between the first lens group and the second lens group. In a telephoto macro lens that has an aperture and focuses mainly by moving the first lens group toward the object side, the aperture is moved toward the object side independently of the first lens group during focusing, This is a focusing method for a telephoto macro lens that is characterized by minimizing the decrease in the height at which the peripheralmost ray of the off-axis light beam passes through the aperture. Further, when the aperture moves in this manner, it is advantageous if the aperture diameter is constant because the structure becomes simple. An example of data of a telephoto macro lens applied to the present invention will be shown below. Here, f・ω is the focal length and half angle of view for an infinite object, WD is the distance from the object point to the first surface, fB is the back focus, r is the radius of curvature of each lens surface, and d
is the lens thickness or lens spacing, N is the d-line refractive index of each lens, and ν is the Abbe number of each lens.

[Table] Function Figure 1 is a diagram to explain the aperture effect, where a is an infinite object and b is a simplified lens configuration diagram when the magnification is equal to the first lens group with a positive focal length. In a telephoto macro lens consisting of a negative second lens group,
An aperture is placed between both lens groups. Note that this figure shows on-axis and off-axis light rays (light fluxes), and the shaded area is the off-axis light flux. If the diaphragm is fixed to the second lens group, when focusing on an infinite object (as shown in Figure 1 a), even if the diaphragm is closed down, the outermost rays of the off-axis rays will pass through the diaphragm surface. Since the point A is used, there is no deterioration in lens performance, but when focusing on a place with a large magnification such as 1x (as shown in Figure 1 b), when the aperture is stopped down, the outermost edge of the off-axis beam Since the point at which the light ray passes through the aperture plane (indicated by the dotted line) is point B, only the marginal off-axis light flux remains, deteriorating the performance around the screen (the off-axis marginal light flux of a telephoto lens generally increases the magnification (large chromatic aberration)
Resulting in. Therefore, in the present invention, as shown in FIG. 1b,
When moving or extending the first lens group toward the object side and focusing in the direction of high magnification, the diaphragm is also moved toward the object side independently of the first lens group, so that the peripheralmost rays of the off-axis rays pass through the diaphragm ( This reduces the decrease in height caused by point C), eliminates the adverse effects of the aperture that occur at high magnification, and maintains high-performance lens performance. Of course, as shown by the arrow in Figure 1b, if the amount of movement of the aperture is not smaller than the amount of movement of the first lens group, the aperture will easily come into contact with the first lens group. The mechanical structure is also difficult. Effects As explained above, according to the focusing method of the present invention, the aperture effect is achieved by moving the aperture toward the object side independently of the first lens group. A high-performance telephoto macro lens can be achieved under these conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the aperture effect, where a is an infinite object and b is a simplified lens configuration diagram when the magnification is the same. A: Point at which the most peripheral ray of the off-axis light beam passes through the aperture surface in the case of an infinite object B: Point C where the most peripheral ray of the off-axis light beam passes through the aperture surface when the aperture position is fixed at the same magnification: The point at which the peripheralmost ray of the off-axis beam passes through the aperture surface in the focusing method of the present invention.

Claims (1)

[Claims] 1. Consists of a first lens group having a positive focal length and a second lens group having a negative focal length, viewed from the object side, and between the first lens group and the second lens group. In a telephoto macro lens that has an aperture and focuses mainly by moving the first lens group toward the object side, the aperture is moved toward the object side independently of the first lens group during focusing, A focusing method for a telephoto macro lens that is characterized by minimizing the decrease in the height at which the peripheralmost ray of the off-axis light beam passes through the aperture. 2. Focusing of a telephoto macro lens according to claim 1, characterized in that the diameter of the aperture remains constant when the aperture moves toward the object side independently of the first lens group during focusing. Ing method.