JPS58118616A - Refraction type optical system for video projector - Google Patents

Abstract

PURPOSE:To realize a refraction type optical system having an F number which is lighter than two and a good performance, by satisfying prescribed conditions to the optical system composed of three groups. CONSTITUTION:From the screen side to the projection tube side, the 1st group Icomposed of an aspherical surface plastic single lens of the positive refracting power, whose convex surface fases to the screen side, the 2nd group II composed of a biconvex glass single lens having an X-ray shielding effect, and the 3rd group III composed of an aspherical plastic lens of the negative refracting power, whose concave surface faces to the screen side, are provided successively. They are arranged so as to satisfy the conditions of formulaeIand II. In the formulae, N represents the refractive index of the group II, (f) represents the focal length of the whole system, and the f1 is the focal length of the 1st group I. In this way, a refraction type optical system for video projector having an F number which is lighter than two can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refractive optical system for a video projector that projects a projection tube image onto a screen.
It is an object of the present invention to provide a refractive optical system that has a brighter F value than 2 and has good performance by using a small number of lenses.

As is clear from FIG. 1, the configuration of the present invention consists of a first aspherical plastic single lens with a positive refractive power and a convex surface facing toward the screen, in order from the screen side to the projection tube side.
group (I), a second group (6) consisting of a biconvex single glass lens with an XI shielding effect, and a third group (ID') consisting of an aspherical plastic single lens with negative refractive power with its concave surface facing the screen side. A video projector with an F value brighter than 2, characterized in that the video projector has the following characteristics and satisfies the following conditions:
It is a refractive optical system for

(1) N> 1.55 (2) 1.2f<f, <2.5f However, N is the refractive index of the second group, f is the focal length of the entire system,
fl is the focal length of the first group.

Further, a more detailed feature of the present invention is the above condition (1).

In addition to (2), the following conditions must also be satisfied.

(3) 1.2<f, /f2<2.5i11shi, f2
&'r is the focal length of the second group.

In carrying out the present invention, it is further desirable to satisfy the following conditions.

(4) 0.3f<D<0.5f where D is the air gap between the second group and the third group.

The present invention will be explained in more detail below.

In the present invention, by using an aspherical plastic lens in the first group (Il), various aberrations mainly including spherical aberration 'kU' can be corrected in a well-balanced manner, and the third group (III
) By using an i/n aspherical plastic lens, the mound surface characteristics are mainly improved. Also, the second group (9)
The glass lens also has the function of shielding the X-rays emitted from the projection tube. There is no need to take countermeasures against false accusations.Next, the conditions of the present invention will be explained.Condition (1) is the second condition.
This specifies the refractive index of the glass lens of the group. If this condition is not satisfied, it will be difficult to obtain a glass material that has an X-ray shielding effect, and the refractive index to give the second group a predetermined refractive power. With a spherical glass lens, the surface curvature becomes steeper, making it difficult to properly balance spherical aberration and other aberrations by ÷11.

Condition (2) defines the distribution of refractive power to the first group, and condition (
3) defines the relative distribution of refractive power between the first group and the second group, which bear positive refractive power. That is, the first
By giving a relatively large positive refractive power to the group and appropriately sharing the positive refractive power in the lens system between the first and second groups, it is possible to balance the correction of axial and off-axis aberrations. Condition (2) (more specifically, conditions (2) and (3)) shortens the total length of the lens and makes the entire system compact.
This is a feature of the present invention represented by the combination of When the lower limit of condition (2) or (3) is exceeded, the power of the first group becomes too strong, resulting in generation of high-order spherical aberration and negative shift of the curvature of field. On the other hand, condition (2) or If the upper limit of (3) is exceeded, the curvature of field will be overcorrected and off-axis sagittal flare will occur. In either case, the on-axis and off-axis aberrations cannot be balanced, making it difficult to construct a bright and high-performance lens system.

Condition (4) gives the air spacing between the second and third groups, and should determine the optimum range for power distribution between the first and second groups. When the lower limit of condition (4) is exceeded, the curvature of field shifts negatively and the astigmatism difference increases. On the other hand, if the upper limit of condition (4) is exceeded, sagittal flare will be insufficiently corrected and the distance between the third group and the projection tube will become extremely close, which is inconvenient in practice.

Next, examples of the present invention will be shown. In the following old 1st statement rl
, rl ・is the curvature half u of each surface of the lens, dtt dz+
... is the wall thickness or air gap between lens surfaces, n engineering, n2
．． ... is the refractive index of each lens for the d-line (light with a wavelength of 587.6ruη), and C2. ... is the Abbe number for the d-line (all Iia from the screen side to the projection tube side).

For surfaces with an aspherical shape (indicated by *), the Y-axis with the projection tube direction as positive is taken from the apex of the surface on the optical axis, and the Y-axis perpendicular to the Y-axis is taken at the same apex. The aspherical shape is expressed by the following equation.

Note that this expression includes the terms HC and Y2, so the near-axial curvature of the aspheric surface expressed by this expression is co+2C1
There's a lot of yelling. (However, C8" 1 /r: r is a half cylinder of curvature as a spherical surface) [Real example] f = 100. β = -0,122, F value 1.o5
1st side (rl) 5th side (r5) c,
o, 26208 X 10"-2-0, 11508X
10-” C2-0゜22078 X 10”” -0,3
8763X 10''''゛C, o, 11738 X 10
-' 0.93770 pieces 1o-.

C4-0, 70595X□. −”.

-0,11151X 10"-" C5-0, 52317X 10 0,45873×10″″ ca o, 57586 X 10-”.

0, 78070 X 10-”.

C, -0,60807A1o-0,82634X 10''''' CB-1+, 98529U1o-280,7630'
9.times.10"-" A lens configuration diagram of the above embodiment is shown in FIG. As is clear from FIG. The 83rd group consists of a plano-concave aspherical plastic single lens (G) with the concave [II] facing the screen side.The third group OID to 7. Thickness 8.5 (n = 1.53
6. νd=50.7), and its right side in the drawing is a fluorescent surface. The aberration diagram of Example 1 is shown in FIG.

As is clear from the above, the present invention provides a refractive optical system for a video projector that has a small number of lenses, has a bright F value, and has good performance as shown in the aberration diagram. ζ et al., since the refractive optical system of the present invention uses a glass lens in the second group, the 11-point shift due to temperature change -1 is the same as when all from the drive 1 group to the optical 3 #1 are made of plastic. There is also the effect that half of the number is 1.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of Example 11 of the present invention, and FIG. 21 is an aberration diagram of Example 1. ■・No. 1 # II...Group 2 ■...Group 3 Applicant Minolta Camera Co., Ltd. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A first group consisting of an aspherical plastic single lens with positive refractive power with a convex surface facing the screen in order from the screen side to the projection tube side, and a biconvex glass unit with an X-ray shielding effect. The second group consists of a lens, and the third group consists of a single aspherical plastic lens with a negative refractive power with its concave surface facing the screen side. 2 Brighter refractive light for video projector N>1.55 1.2f<fl<2.5f However, N is the refractive index of the second group, f is the focal length of the entire system, and fl is the first group. focal length. 2. The refractive optical system according to claim 1, further satisfying all of the following conditions: 1.2 and f, /f<2.5, where f2 is the second group focal length. 3. The refractive optical system according to claim 1 or '2, which is further characterized by satisfying the following condition: 0.3f<D<0.5f, where D is Air spacing between the second and third groups. 4. A refractive optical system according to any one of claims 1 to 3, characterized in that surfaces of the first group and the third group on the projection tube side are flat.