JPS5862611A - Optical device for variable image magnification - Google Patents

Abstract

PURPOSE:To increase the variable magnification ratio, by moving mechanically a negative front group and a positive rear group on the optical axis to vary magnification and changing the interval between the front group and the rear group in opposite relations between <=-1 and >=-1 image magnifications. CONSTITUTION:In case that a titled or the like is inserted by super-imposition, it is noticed that the total track between a object and an image surface is constant, and lenses are moved as shown in figure to vary magnifications. A total track T between an object O and an image surface I is constant, and a negative front group L1 and a positive rear group L2 are moved on the optical axis. The magnification is varied from the minimum to the maximum as shown in figure by A-D. Lenses L1 and L2 are so moved that an interval l is minimum for magnification m=-1 (C) and is reduced from the minimum magnification to m=-1 and is increased from m=-1 to the maximum magnification. Thus, the variation of the interval l is reduced to increase the variance of magnifications.

Description

[Detailed Description of the Invention] For example, if you want to see a title on an image shot with a video camera, such as by imposing, you can freely and significantly change the image magnification of the video camera. If possible, when using handmade letters or handles as a title, the size will not be split, which is convenient, and can even be used to create a more effective title.

A zoom optical system (focal length variable optical system) is an optical system that can freely change the image magnification in this way. This zoom optical system is generally of a type called a two-group type or a 4# type, or a variant thereof.

FIG. 1 shows a two-group type zoom optical system, where Ll is a front group with a negative focal length, L2 is a rear group with a positive focal length of d, and ■ is the body surface. Then, while keeping the position of the image plane (■) constant, both groups Ll s L2"L' are moved in a 4#! range on the optical axis to change the focal length. Figure 1B shows the state when the focal length is set to the maximum (telephoto).

However, with this zoom optical system, The power of the whole system ll: Power of front group L1 zza & power of group L2 J: Corner between front #Ls and rear group L2 given that, A = hook ten! 2-4 da 1g62 The relational expression holds true.

Therefore, in a zoom optical system, when the zoom ratio is increased in order to increase the image magnification, the interval 1 becomes longer, the lens sweep becomes larger, and at this time, it becomes difficult to correct lens aberrations. For this reason, with conventional zoom optical systems, it is difficult to greatly change the image magnification of the entire system, and even if it were possible to change the image magnification greatly, it would be difficult for general users due to cost and size. cannot be provided.

In view of these points, the present invention aims to provide a low-cost and compact optical system that can continuously and significantly change the image magnification.

For this reason, in the present invention, for example, when shooting a title, we pay attention to the fact that the total track between the subject and the blush is constant, and move the front and rear groups as shown in FIG. Change the magnification.

In other words, Nagi "c", 'O is the subject, ■-
The total track T between the subject 0 and the image plane (2) is assumed to be constant. In addition, t, Bit has a negative focal length and the front group L2 has a positive focal length.

Both units L1 and L2 move on the optical axis A to change the image magnification. Figure 2 A shows the state when the image magnification is at its maximum /J-Q, and the second diagram shows the state when the image magnification is at its maximum. The state of time, happiness 2
Figures B and C show intermediate states.

In addition, curve C11C2 shows that both groups L1 and L2 are JIEg
The trajectory of the center of both groups L1 and L2 when changing between the state of Figure A and the state of 812 diagram is shown.

That is, in Fig. 2, fl: focal length of the front group f2 = focal length T of the rear group L2, track J: distance m between the front group and the rear group L8: image magnification of the entire system. : Image magnification m2 formed by the front group L1 with subject 0: Image formed by the rear group L2 with image based on preview 1, :11. ''' Magnification ■: Image magnification mT when 1 m1 is the minimum: l m Image magnification m1 when l is the maximum w; The image taken by the front group LIK when the magnification is Gin is shown in the rear #
Image magnification Δl at which L2 forms an image: Amount of movement of m group L1 with respect to the change in magnification from the image magnification Δ2 = * Amount of reduction in interval 1 for the gray magnification from the magnification Δ3: Change in magnification from the image magnification When the amount of movement of Wt group L2 relative to
4!r4IL is set so that 1 ml mlW Δs ”! (fllz − mgw ) h 1.

Then, as shown in Fig. 2 CK, the interval 1 is minimized when nl x-1, and for scaling to m = 0% tm = -1, the interval J decreases, and m = -1. 1 to m = m
For zooming to '1', both groups L1 and L2 are moved on the optical axis A so that the distance J increases.

Note that the means for moving both groups L1, L, ′□ can be configured in the same way as in the conventional case, for example, curves C1′, C! A guide groove corresponding to the curve is formed so that both #1#L1 and L1' can move □ from these K.
In this case, according to experimental and computer simulations, 1≦l f)'t, + < 1-. 80.07 (f
2/'r' (0,2 It was practical to set J<4.5f2. A specific numerical example is shown in Figure 3. That is, according to this numerical example, the front group The distance J between L1 and the rear group L2 is 80 mm (image -
You can change the ratio by up to 30 times. - In this way, according to the present invention, since the magnification is changed by reversing the change in the distance 4 after m=-1, the image does not need to be changed greatly in the distance J as shown in i above. The magnification m can be continuously and largely changed. Also, the interval J
Since the amount of change is small, a large variable power ratio can be obtained with a two-group type optical system, which is the simplest configuration for a variable power optical system.

Furthermore, since the amount of change in the interval 1 is small, the lens diameter only needs to be small, and aberrations can be easily corrected, making it compact and low cost.

[Brief explanation of drawings]

Striped IWjA, Figure 3 is a diagram for explaining this invention, and Figure 2 is a system of an example of this invention. Ll is # group, L! is the rear group, 0 is the subject, and ■ is the image plane.

Claims (1)

[Claims] It consists of a front group with a negative focal length and a rear group with a positive focal length. In a variable magnification optical device that is mechanically moved on an axis to change the image magnification of the entire system, the front group and the rear group are separated from each other when the image magnification is -1. Change the interval to an inverse relationship,
An optical device for changing image magnification that enlarges the image magnification by increasing the magnification.