JPS61248013A - Projection lens for television projector - Google Patents

Abstract

PURPOSE:To obtain a lens having large aperture and wide angle of view by satisfying the composite focal distance of the whole system, the composite focal distance of the 1st and 2nd lenses, the radius of curvature of the vertex of the surface of the 3rd lens on the screen side and the radius of curvature of the vertex of the surface of the 3rd lens on the opposite side to the screen with specific conditions. CONSTITUTION:When it is defined that (f) is the composite focal distance of the whole system, f12 is the composite focal distance of the 1st and 2nd lenses, r5 is the radius of curvature of the vertex of the surface of the 3rd lens on the screen side, and r6 is the radius of curvature of the vertex of the surface of the 3rd lens on the opposite side to the screen, respective lenses are constituted so as to be satisfied with the conditions of the inequality. The 1st lens which is a negative meniscus lens is made aspherical to compensate comatic aberration effectively in a meridional direction at a position of a large angle of view. If the upper limit of the condition 1 is exceeded, it becomes difficult to compensate the comatic aberration at the aspheric surface of the 1st lens. If the lower limit of the condition 1 is exceeded, the refractive power of the 3rd lens should be increased. If the upper limit of the condition 2 is exceeded, the comatic aberration of a high degree is generated. If the lower limit is exceeded, its sine condition is deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a projection lens for a television projector, particularly a 4C3 tube type projection lens for a television projector.

(Prior art) A television projector uses a projection lens to enlarge and project the screen of a private ray tube onto a screen, but a three-tube type projector uses blue (B), green (G), and red (R) fluorescent light. A color image is obtained by projecting the electric charge onto the screen using one lens from each of the three ray tubes that have a body. In this case, each lens projects only one color, so there is no need for achromatization.

Plastic lenses are used in such lens systems due to the need to reduce costs and make them lightweight.
No. 14, No. 57-34515, No. 1088 of No. 57-1988
No. 18, No. 177115 of 1983, etc. are known.

These are 3 sheets with a small number of sheets and an F number of 1.0
A large diameter projection lens of about 1.3 mm has been obtained.

In recent years, as projection lenses have become larger in diameter, lenses made only of plastic lenses have become increasingly popular in television projectors.
There is a problem in that the projected image deteriorates due to fluctuations in back focus due to temperature changes within the device.

As a temperature change compensation method to solve this problem, there is a method of focusing by providing a mechanism that automatically moves the lens according to the AT change, and a method of focusing the projection lens! ! Devices that keep If constant are conceivable, but none of them can prevent the device from becoming vj, sloppy, and increasing in cost.

On the other hand, among these types of lens systems, it has been proposed that the projection lens be constructed by appropriately combining a spherical glass lens and a plastic lens to reduce fluctuations in back focus due to temperature changes. Examples of three-sheet configurations include JP-A-58-118616 and JP-A-58-125007. In these lens systems, the second lens is a spherical glass lens, and coma aberration occurs at large angles of view.

Additionally, there is a problem that the sagittal flare is large and the contrast at the periphery of the screen is low. In addition, as for the four-sheet composition, Japanese Patent Application Laid-open No. 56-78815,
No. 311 and No. 59-155818 are known. However, the first two types have large comatic aberrations at large angles of view, making it difficult to increase the aperture. On the other hand, the latter has a drawback that the overall length is long and the amount of peripheral light is small because a mirror for refracting the optical path is built into the lens system.

(Problems to be solved by this invention) This invention has a large aperture with a mouth-to-toe ratio of about 1.04 to 1.1 and an angle of view of 24 to 2.
The objective is to obtain a lens for a television projector that has a wide lens width of 8, has well-corrected aberrations, and is less affected by temperature changes even though it uses a plastic lens.

Structure of the Invention (Means for Solving Problems) In the present invention, the projection lens system includes, as shown in FIG. , a second lens that is a positive lens with a convex surface facing the screen side, a third lens that is a biconvex lens, and a fourth lens that is a negative lens with a concave surface facing the screen side, and at least one of the first lenses.
The surface is aspherical, and f: Combined focal length of the entire system f12: Combined focal length of the first lens and second lens rs:
Vertex radius of curvature of the screen-side surface of the third lens "6: 0.15 as the vertex curvature radius of the surface of the third lens opposite to the screen ＜'/f <0.7-2.0
It is configured to satisfy the condition <rs/r6<-0,45.

Furthermore, it is desirable to satisfy the following secondary conditions: '5: I'E; radius of apex curvature of the screen-side surface of the second lens; n2: K: refractive index of the second lens; f2: focal length of the second lens.

Also, plastic lenses are introduced into the first lens and the third lens.

(Function) Of the above lens configurations, the first lens, which is a negative meniscus lens, has at least one surface aspherical to effectively correct coma aberration in the meridional direction at large angles of view. 25 things to increase the contrast in! can.

Condition (]) is the combined focal length A of the first lens and second lens.
2, if the upper limit is exceeded, the refractive power of the second lens becomes too large, resulting in large extrinsic coma aberration, which becomes difficult to correct with the aspheric surface of the first lens. When the lower limit is exceeded, it becomes necessary to increase the refractive power of the third lens. As a result, the internal nocoma aberration becomes large at large angles of view, leading to a decrease in contrast (IF). To correct this, the third lens must be made of a material with a high refractive index, or two lenses must be It becomes necessary to divide the lens into positive lenses, leading to an increase in the cost of the lens.

Condition (2) relates to the shape of the third lens, and if the radius of curvature of the screen-side surface of the third lens becomes small beyond the upper limit, the light flux will be directed to the screen-side surface of the third lens in the part with a large angle of view. The incident angle of the lens becomes large, and high-order coma aberration occurs. On the other hand, if the lower limit is exceeded and the curvature force on the screen side of the third lens becomes looser, the sine condition deteriorates.Furthermore, if the upper limit of condition (3) is exceeded, the occurrence of spherical aberration increases, and the lower limit is exceeded. When it exceeds and becomes smaller, the second
The angle of incidence on the screen-side surface of the lens increases, causing high-order coma aberration.

In the lens system of this invention, the second lens with large refractive power is a spherical glass lens, and the first and third lenses are aspherical plastic lenses, so that there is no influence on lens performance, and there is no pack due to temperature change. Focus fluctuations can be reduced. In addition, since the first lens is a negative lens, it is made of a plastic material with a small Atsushi number.
By using -i, chromatic aberration can also be improved.

(Example) Examples of the projection lens of the present invention will be shown below.

In the table, ri is the vertex curvature of the first lens surface from the screen side #? i and di are the distances between the first lens surfaces from the screen side, ni is the refractive index of the first lens material from the screen side at a wavelength of 5431 m, and νi is its Abbe number. In addition, for an aspherical shape, in an orthogonal coordinate system with the apex of the surface as the origin and the optical axis direction as the
Pi) 2.0), it is expressed as φ=G〒T.

Nao, the table also shows the orientation of the face plate G.

Example 1 f=103.50 Mouth to toe ratio 1:1.04 fl
! r car-0,1355ri cHni νi 1 112.307 4DO1,59200
30,0291,4366,00 397B3919.00 1.59162 61.04
-1779.33159f145
15630721.00 1.49425 55.06
-113fi8356.90 Example 2 Example 3 Example 4 Example 5 Effects of the Invention The projection lens system of this invention has a large aperture ratio of 1.04 and an angle of view, as seen in Example 4. Although the lens has a wide angle of view with a deviation of about 27 degrees, various aberrations are well corrected as shown in the aberration diagrams shown in FIG. 2 or IES diagram.

Example 5 has a slightly smaller aperture ratio of 1.1 and an angle of view of 2.4, although the air gap between the wc2 lens and the third lens is large and it is possible to incorporate a plane mirror. , as seen in FIG. 6, the aberration correction is good.

In either case, the optical system is compactly constructed, making it possible to downsize the television glodictor.

9. As seen in the examples, the second lens with strong positive refractive power is a spherical glass lens, and the first lens is ts3.
By making the lens a plastic lens, the effect of temperature changes is reduced, the cost is reduced, and it is easy to make it aspherical. Note that the fourth lens is a very large negative lens, which increases the cost. By using a plastic lens for this lens, costs can be reduced. Furthermore, as shown in FIG. 7, the meniscus lens Lm
It is possible to make a composite lens with a liquid lens Lq and a liquid lens Lq, thereby reducing the cost of the lens, preventing reflections between the face plate side surface of the fourth lens and the face plate, and improving the contrast at the projection edge. You can measure the rise.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the lens configuration of this invention, FIG.
FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are aberration curve diagrams of Examples 1 to 5, respectively, and FIG. wX7 is a sectional view showing a modification of the fourth lens using a liquid lens. Patent applicant Roku Konishi Photo Industry Co., Ltd. Patent attorney Fumi Sato (1 person) Figure 1 Army 2Ii21 R-plane aberration Astigmatism Distortion aberration Coma Figure 3 Spherical aberration Astigmatism Distortion Aberration No. 4 Spherical aberration Astigmatism Distortion aberration collection 5 Spherical aberration Astigmatism Distortion coma aberration 6 Spherical aberration Astigmatism Distortion aberration Comatic aberration Fig. 7 L4' G

Claims (1)

[Claims] In order from the screen side, the first lens is a negative meniscus lens with a convex surface facing the screen side, the second lens is a positive lens with a convex surface facing the screen side, the third lens is a biconvex lens, and the screen. Consists of a fourth lens which is a negative lens with a concave surface facing the side, at least one surface of the first lens is an aspherical surface, and f: composite focal length of the entire system f_1_2: composite focal point of the first lens and the second lens Distance r_5: radius of apex curvature of the screen-side surface of the third lens r_6: 0.15<f/f_1_2<0.7 -2.0<r_5/ as the vertex curvature radius of the surface of the third lens on the opposite side to the screen A projection lens for a television projector, characterized in that it satisfies the condition r_6<-0.45.