JPS5883805A - Zoom lens for projector - Google Patents

Abstract

PURPOSE:To shorten the movement distance, by changing freely air intervals of three lenses in the direction of the optical axis and setting the resultant focal length, radiuses of curvature of respective faces, thicknesses of lenses, and intervals of faces of lenses to prescribed values. CONSTITUTION:A biconvex lensI, a biconcave lens II, and a convex meniscus lens III are provided in order from the screen side, and air intervals of these lenses are changed freely in the direction of the optical axis to perform zooming. Equations are satisfied when the resultant focal length is denoted as (f) and radiuses of curvatures of the first - the sixth faces are denoted as R1-R6 and the thickness of the first lens, the intervals between faces of the first lens, the thickness of the second lens - are denoted as D1-D5 respectively. In figure, lenses for telephoto zoom and lenses for wide angle zoom are shown.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens for use in a projector such as an overhead projector.

0. . . Knee 1°7. '8th grader. Yo.

It is an object of the present invention to provide a zoom lens for a projector that can be used up to telephoto and has a small movement distance.

Another object of the present invention is to provide a zoom lens that can contribute to making the projector body more compact and lightweight by making the structure of the lens system smaller and lighter without deteriorating its performance. It is.

An overhead projector is a device that enlarges and projects characters, graphics, graphs, etc. on a transparent sheet onto a screen, and is widely used in educational facilities such as schools as well as various training facilities.

These overhead projectors usually need to project clearly onto a screen with an angle of view of about 10 inches diagonal length 280φ, and at the beginning of development, a lens with a focal length of about /=320 was used, but gradually the focal length was /=3007=270. Recently, /=240 has become possible due to improvements.

However, as mentioned above, the lenses used in these conventional projectors are fixed focal length lenses such as /=270 or /=240, so they only project the entire surface of the original sheet at the same time, and are similar to zoom lenses. It was not possible to zoom in and project a specific part of a manuscript. When performing projection using a projector, it is extremely desirable that the lens used for projection be capable of continuously covering the range from wide-angle to telephoto.
As mentioned above, if you try to use a zoom lens that can cover an angle of view with a diagonal length of 280φ from among the known lens systems, at least LlLzlL as shown in FIG.
a, L4041'? Ls in a zoom lens system consisting of 4 elements
It is necessary to use a configuration that combines three master lenses in three groups consisting of fixed lenses of . Currently, projectors such as overhead projectors used in schools, etc. are
Most of the equipment is carried around, set up, and then stored again after use, and since many of the people who operate it are female teachers, it is desired that the equipment be compact and lightweight. For this reason, if a known zoom lens with the above-mentioned configuration is used, these requirements cannot be achieved at all, and furthermore, the use of multiple lens systems causes high costs, so in the end, a projector equipped with a zoom lens cannot be used. was not put into practice.

The present invention deals with these. The object of the present invention is to provide a zoom lens for a projector that can eliminate the drawbacks, and by completing the invention described below, the object has been fully achieved.

Hereinafter, embodiments of the present invention will be explained with reference to all the drawings.

That is, the present invention consists of a combination of three lens groups, each lens being a biconvex lens (I), a biconcave lens (in), and a convex meniscus lens (II) in order from the screen side, and the air distance between them can be freely changed. It performs zooming by the combined focal pressure Ill/.

When the radius of curvature of each surface is tR, the lens thickness, and the lens interval are D, f = 1.0 R, = +0.26 to 0.33 D, = 0.02
~6.04Ry=0.40~0.48Dt
=0.005~0.05R,=-0,19~0123
D,=0.005~0.007R4=+0.38
~0.47 D4=0.01 ~0.07R,=-
0.28 ~ 0.38 D, = 0.03 ~ 0.05
All characteristics are that Rs=0.14 to 0.20.

Fig. 2<4) A configuration diagram of a lens showing an embodiment of the present invention (particularly showing Te1e5#) when Fif = 300,
#I2 Figure (b) is a configuration diagram of a lens showing an embodiment of the present invention (particularly shown) when /=240.

As is clear from the examples, according to the present invention, the configuration of the lens group is Te1e/=300''?'Dt=2.
4 Ds=4.2 Lens length 26.9%, also wide
e f=240 ”t'D,=10.OD,=12
．． 5 The above-mentioned 2 with a configuration of lens length 42.8%
It is possible to perform projection that sufficiently covers an angle of view of 80φ, and it is possible to obtain an extremely compact zoom lens for a projector with a maximum lens length of 42.8%.

The present invention has a structure in which zooming is performed by freely changing the air spacing of the three lenses (i), (n), and (b) described above, without using a conventional zoom lens. Even when doing this, the amount of lens movement is a small distance of about 16% (15.9%)1, which contributes to improving resolution and contrast, and also reduces chromatic aberration and distortion. I was able to summarize it in a small way.

Furthermore, according to the present invention, since the amount of lens movement is small as described above, it is possible to fully take in all of the oblique rays. It has many features such as being able to

[Brief explanation of the drawing]

FIG. M1 is a configuration diagram showing a conventional zoom lens system, and FIG. 2 is a lens configuration diagram showing a zoom lens according to the present invention, where 0) and 2) show the telephoto state and (b) the wide-angle state, respectively. (1)...biconvex lens, (season...biconcave lens, (2)
)...Convex meniscus lens Fig. 1 Fig. 2

Claims (1)

[Claims] A zoom lens in which a biconvex lens, a biconcave lens, and a convex meniscus lens are sequentially arranged from the screen side, and the air distance between these lenses can be freely changed in the optical axis direction to perform zooming. Then, the combined focal length is 11. When the radius of curvature of each surface is R1, the lens thickness and the lens interval, then /=1.0 R, = +0.26~0.33 Dt=0.02~0,
04R2=0.40~0.48 D Goose 11
jj=-0,19~0.23 Ds=0.005~0
．． 007R,=+0.38~0.47 D4=0.
01~0.07R,=-0,28~0.38Ds
=0.03~0.05゛R6=-0.14~0.20 A zoom lens for a projector.