JPS6111717A - Projecting lens - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in performance owing to a temp. change by using plastic lenses for the lenses having the small absolute value of refracting power of a front lens and intermediate lens groups and using a glass lens for the lens having the positive refracting power of the intermediate lens group. CONSTITUTION:The 1st lens made of the plastic having the positive refracting power, the 2nd lens made of the glass which directs the convex face having the radius of curvature larger than the radius of curvature on the screen side lens face toward the original picture image side and having the positive refracting power as the intermediate lens group and the meniscus 3rd lens made of the plastic directing the concave face toward the original picture image side are used for the projecting lens. The 1st lens having the weak and positive power is made of the plastic lens, the 2nd lens having the strong positive power is made of the glass lens and the 3rd lens having the weak positive power and consisting of the meniscus lens is made of the plastic lens. The performance change with the temp. change is thus considerably suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection lens, and particularly to a projection lens that is suitable for enlarging and projecting an image projected on an electronic imaging device onto a screen and that is not affected by changes in temperature. Sekisuya.

In general, a projection lens for displaying images uses monochromatic cathode ray tubes in three colors of red, blue, and green for displaying color images, and each image is projected onto a screen by the projection lens.
It is not necessary that the lens be a false achromatic lens that has relatively narrow color development characteristics and spectral width.

Desirable conditions for a projection lens include a large aperture and a wide angle of view. The large aperture makes it possible to obtain a bright image, and the wide angle of view makes it possible to obtain a desired projected image at a short projection distance, making it possible to downsize the entire device.

Conventional projection lenses include spherical lenses with only spherical surfaces and aspheric lenses with aspherical surfaces, but with spherical lenses, it is extremely difficult to reduce the number of constituent elements and improve performance, so in recent years, non-spherical lenses that incorporate aspherical surfaces have been used. Spherical lenses are the mainstream.

However, the history of a projection lens itself that uses an aspheric surface to correct aberrations is long, and British Patent No. 593,514 is known. The projection lens disclosed in this patent is, in order from the image plane side, a first group that is a laminated lens of a biconvex lens and a biconcave lens and has an aspherical surface at 814 to correct aberrations that mainly depend on the aperture and axial chromatic aberration; It consists of a positive second group consisting of two plano-convex lenses with their convex surfaces facing the screen side, and a third group having negative refractive power for image flattening means. According to this configuration, among the aberrations of spherical aberration, image curvature, and coma aberration, spherical aberration and coma aberration are corrected by the first lens group, and field curvature and distortion aberration are corrected by the third lens group. The correction of spherical aberration and coma aberration corrected by this method is insufficient, and the correction of coma aberration is particularly poor.

Furthermore, since all the constituent lenses are made of plastic lenses, there is a problem with the characteristics associated with temperature changes. This is because the performance drift of plastic due to temperature changes is an order of magnitude larger than that of glass, so the temperature drift of the focal position due to temperature changes in the atmosphere in which the lens is placed is extremely large, which is thought to be a major constraint in practical use. It will be done. SUMMARY OF THE INVENTION An object of the present invention is to provide a lens that has a wide angle of view, has good image quality, particularly coma aberration correction, and does not suffer from deterioration in performance due to temperature changes.

In order to achieve this purpose, in order from the screen side, a front lens with a positive refractive power, an intermediate lens group having a lens with a positive refractive power and a lens with a smaller absolute value of refractive power than this lens, and a concave surface as a screen. A rear lens facing toward the side is used, the refractive power of the intermediate lens group is greater than the refractive power of the front lens, and a plastic lens is used for the lens in which the absolute value of the refractive power of the front lens and the intermediate lens group is small.
A glass lens is used as a lens with positive refractive power in the intermediate lens group.

The projection lens of the embodiment shown in FIGS. 1 to 3 consists of, in order from the screen side, a plastic tube lens (device lens) having a positive refractive power, and an intermediate lens group with a radius of curvature compared to the side surface of the screen. A second lens made of glass with a positive refractive power with a large convex surface facing the original image side, and a third meniscus lens made of plastic with a concave surface facing the original image side, and a third lens with a meniscus made of plastic with a concave surface facing the original image side. It consists of a fourth glass lens (rear lens) with a larger curvature and a concave surface facing the screen side.

Next, the effects of the above-described configuration will be described.

The second lens has one or more aspherical surfaces to correct aberrations that mainly depend on the aperture, the second lens has positive refractive power mainly for image formation, and the third lens is on the picture tube side. It is a meniscus lens with a concave surface that has a weak positive refractive power, and in order to minimize the occurrence of aberrations in the axial light beam, it has a shape close to that of a concentric or horizontal ray, which eliminates aberrations that depend on the angle of view and off-axis light beams. Aberrations, especially comatic aberration, are well corrected, and the fourth lens has a concave surface with a large curvature facing toward the screen, thereby correcting field-angle dependent aberrations, especially image curvature and distortion. Furthermore, in order to improve the correction of these off-axis aberrations and realize a wide field of view of more than 25 degrees, the second
．． Third. The fourth lens has at least one aspherical surface to improve performance.

That is, among spherical aberration, coma aberration, field curvature, and distortion, the spherical aberration and coma aberration are corrected by the third lens, the coma aberration is corrected by the third lens, and the field curvature and distortion aberration are corrected by the fourth lens. The meniscus-shaped lens arranged as a lens effectively corrects coma aberration, and by making it concentric or close to concentric, the occurrence of axial aberration is suppressed as much as possible, achieving extremely high performance. ing.

In particular, in this example, the second lens with weak positive power is a plastic lens, the second lens with strong positive power is a glass lens, the third lens is a meniscus lens with weak positive power, and the third lens is a plastic lens with strong negative power. The fourth lens is made of a glass lens, and the second lens has a particularly strong positive and negative power. By using glass as the fourth lens, changes in the performance of the entire lens system due to temperature changes in the atmosphere are significantly suppressed.

Although the object of the present invention has been achieved as described above, when actually designing a lens, by considering the following matters, it is possible to correct aberrations to a higher degree and to shorten the design time.

(1) The radius of curvature R of the screen side surface of the third lens,
(wRs), the radius of curvature of the surface of the third lens on the picture tube side is f
i, (wz R6), the following formula is satisfied.

0.45<R, /R,<0.85 This condition relates to the power sharing ratio between the front and rear curvature radii of the third lens and the degree of meniscus, and when the lower limit is exceeded, the power of the third lens increases.

The amount of aberration generated in axial and off-axis light beams increases, making it difficult to correct coma aberration, which is the main objective.

If the upper limit is exceeded, the power of the third lens becomes very weak, the burden of power on the second lens increases, the amount of aberration generated by the second lens increases, and aberration correction becomes difficult.

(2) When the refractive power of the intermediate lens group consisting of the second lens and the third lens is φ, and the refractive power of the entire system is φ, the following formula is satisfied.

0.75(φ1/φ(0.9ft) The positive condition is related to the combined power of the second and third lenses, and when the lower limit is exceeded, the share of power by the first lens becomes large, making it difficult to correct spherical aberration. When the upper limit is exceeded, off-axis aberrations caused by the second lens and the third lens, mainly the second lens, become large, making correction difficult.

This is, for example, the second. When the positive power of the third lens increases,
In order to correct the curvature of field, it is necessary to increase the negative power of the fourth lens, which increases the occurrence of aberrations such as distortion, making it difficult to achieve high performance.

(3) It is preferable to consider the following conditional expression, and when it is assumed that the distance between the surfaces of the first lens and the second lens is satisfied, the following expression is satisfied.

0.4 f<D, <o, 6 f This condition relates to the distance between the first lens and the second lens. When the lower limit is exceeded, the imaging power of the off-axis light beam is insufficient, and the second
．． Third. This increases the burden of imaging the off-axis light beam on the fourth lens, which becomes a major obstacle to widening the angle of view. When the upper limit is exceeded, the angle of incidence of the off-axis light beam on the rear surface of the second lens, that is, on the picture tube side becomes large, and the amount of aberration generated in the off-axis light beam becomes large.

The lens data of the example will be described below.
,... is the radius of curvature of each lens surface, D, , D,...
・ is the wall thickness or air gap between lens surfaces, Nt, N,...
is the refractive index of each lens for the e-line (light with a wavelength of 546.1 nm), and V, ν, . . . are the a, ve numbers for the e-line.

Also, the focal length 1iJ#F is normalized to 100.

The shape of the aspherical surface is defined as the displacement in the optical axis direction in rectangular coordinates with the optical axis direction as the X axis.
/H'' + BIM' + C/H' + D/H' is a symmetrical aspherical surface.

However, H: Height from the optical axis R: Radius of curvature of the apex A, B, C, D, Fl, A/, B', C/, D': Aspherical coefficient % Agony - Agony jump γ mouth X 1χ Agony Sonko
t 啼'-00每Gd d-4td(l(Rumor Φ's ψ ME-Ren C10View-
Figures 1, 2, and 3 show optical arrangement diagrams of each of the above embodiments. In each figure, , L, ... represent each lens, S
is the liquid placed between the projection lens and the picture tube, and P is the glass on the picture tube.

4, 6, and 6 are aberration curves (spherical aberration, astigmatism, and lateral aberration) in each of Examples 1 to 3.

Note that M indicates a meridional image plane, and S indicates a sagittal image plane.

As described above, according to the present invention, the half angle of view is 306 or more, the aperture ratio L
: It is possible to provide a high-performance projection lens that has a large aperture of X,2 or more, a wide angle of view, excellent imaging performance, and is not affected by temperature changes.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are cross-sectional views of lenses showing embodiments of the present invention, respectively. FIG. 4, FIG. 5, and FIG. 6 are aberration curve diagrams of examples, respectively. D is the surface spacing. Applicant: Canon Co., Ltd. 6. J! Tank convergence m aberration procedure correction document (spontaneous) 10/98/1980 Manabu Shiga, Commissioner of the Patent Office, 1988 Patent Application No. 132298 2, Name of the invention Projection lens 3, Relationship with the case of the person making the correction Patent Applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (100
) Canon Co., Ltd. Representative Ryu Kaku Part 4 Address of Agent 3-30-25 Shimomaruko, Ota-ku, Tokyo 14B Description subject to amendment 6 Contents of amendment (1) Bottom line of page 8 of the specification Correct the phrase ``positive condition'' to read ``r main condition.'' (2) After “preferably” on page 1, line 11 of the specification, “
Add "Furthermore." (3) Delete line 8 of page 1 O of the specification. (4) R5 of Example 1 on page 11 of the specification is “47°41
3" is corrected to r74.413J.

Claims (6)

[Claims] (1) The projection lens for projecting the original image onto the screen has, in order from the screen side, a front lens with positive refractive power, a lens with positive refractive power, and a lens with a smaller absolute value of refractive power than the front lens. It is equipped with an intermediate lens group and a rear lens with its concave surface facing the screen side.The refractive power of the intermediate lens group is greater than the refractive power of the front lens, and the absolute value of the refractive power of the front lens and intermediate lens group is A projection lens that uses a plastic lens for the small lens and a glass lens for the positive refractive power lens in the intermediate lens group. (2) The projection lens according to claim 1, wherein the rear lens uses a plastic lens. (3) The intermediate lens group includes, in order from the screen side, a front lens with a positive refractive power that has a larger curvature than the side surface of the screen and has a convex surface facing the original image side, and a front lens that has a concave surface facing the original image side. 2. A projection lens according to claim 1, comprising a meniscus rear lens. (4) The radius of curvature of the screen side surface of the rear lens is R
_3, when the radius of curvature of the side surface of the original image is R_0, 0.4
The projection lens according to claim 1, which satisfies the condition: 5<R_3/R_0<0.85. (5) The projection lens according to claim 1, which satisfies the condition 0.75<φ_i/φ<0.95, where the refractive power of the intermediate lens group is φ_i and the refractive power of the entire system is φ. . (6) The projection lens according to claim 1, wherein the front lens has at least one aspherical surface, and the portion from the intermediate lens group to the rear lens has one or more aspherical surfaces.