JP2010113193A - Projection lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection lens that has a greater image circle, shorter overall length, and longer back focus, maintains high performance, is compact, and is composed of the reduced number of lenses. <P>SOLUTION: In a projection lens composed of three lens groups, the third lens group being a rear group, which is disposed near a diaphragm, is composed of five lenses. The three lenses, which are negative, positive, and negative lenses in this order closest to the diaphragm, are integrally cemented. The remaining two lenses are positive lenses. The entire third lens group, which is the rear group, is positive. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a projection lens including three lens groups, for example, a projection lens for a front projector that can have a large image circle (image forming element surface) and can have a short overall length and a long back focus. The projection lens of the present invention can be suitably used for a series of projection lenses for enlarging and projecting an image displayed by a digital micromirror element (DMD) or the like.

  Conventionally, as shown in Patent Document 1, for example, the lens includes three lens groups, and the third lens group closest to the image forming element has three lenses, a negative lens, a positive lens, and a negative lens, for achromatic purposes. There is known a projection lens in which a cemented lens is cemented.

  Further, for example, as shown in Patent Document 2, a negative lens having a large curvature on the minimum side from a position close to the stop of the third lens group closest to the image forming element side and both surfaces are convex. A cemented lens formed by bonding two positive lenses, a convex meniscus aspheric lens on the reduction side, and a positive lens having a large curvature on the reduction side, and the rear group (the rear group of the second lens group II (reduction) Side) IIr) A projection lens having a total of four lenses is known (Patent Document 2, Claim 1).

  Further, for example, as shown in Patent Document 3, a positive lens having two lenses, a positive lens having a large curvature on the enlargement side, and a negative lens having a large curvature on the reduction side in order from a position close to the stop of the second lens group. A projector optical system in which a cemented lens is formed by bonding two positive lenses having convex surfaces on both sides, a meniscus negative lens having both surfaces aspherical and convex on the reduction side, and a positive lens having a large curvature on the reduction side. Is known (Claim 1 of Patent Document 3).

In addition, for example, as shown in Patent Document 4, three lenses of a negative lens, a positive lens, and a negative lens are arranged at a position closest to the stop among the third lens group that is composed of three lens groups and is closest to the image forming element. There is also known a projection lens such as a projector optical system in which a cemented lens in which a single lens is cemented is arranged and has a total of eight lenses.
See US Pat. No. 7,173,777, FIGS. 2A and 2B. See Japanese Patent Application Laid-Open No. 2004-333688, FIG. See JP-A-2005-173494, FIG. US Pat. No. 7,423,819, FIG. See 2

  By the way, since the projection lens for DMD is a prism used in the illumination optical system, a long lens back is required. On the other hand, particularly in a front projector, the entire length of the projection lens is required to be short because the casing is exposed to the outside. This conflicting requirement inevitably increases the number of sheets and complicates the configuration.

  In addition, along with the miniaturization of image forming elements, axial chromatic aberration and lateral chromatic aberration are highly corrected, and flare (a phenomenon in which spots spread due to aberrations, so-called “bleeding” of the projected image) is small and high resolution is achieved. The design to demonstrate is required.

  On the other hand, among the conventional lens systems, Patent Document 2 does not show a three-lens cemented lens of a negative lens, a positive lens, and a negative lens. In order to realize a compact projection lens with a wide angle of view, high resolution, long back focus and high telecentricity, and the optical path of the imaging light beam is bent between lens groups, The lens system is configured so that “the largest air interval in the lens system is formed between the first and second lens groups in which the reflecting means M is disposed”. That is, the projection lens disclosed in Patent Document 2 is a rear projection lens.

  Here, the panel shift which is the difference between the projection lens for the rear projector and the projection lens for the front projector will be described with reference to FIG. When an image formed on an image forming element is projected onto a screen through a projection lens, the image forming element (= panel) is projected below the optical axis of the projection lens as shown in the lower diagram of FIG. An image can be formed above the optical axis. This is a function necessary for a front projector that is installed on a desk. On the other hand, the rear projector does not need the function as described above, and has a configuration in which the image forming element and the projected image are arranged on the same optical axis as shown in the upper diagram of FIG. From the above description, the projection lens for the front projector that requires panel shift needs to have a larger image circle (= size of the image forming element surface) than the projection lens for the rear projector that uses the same panel.

  The projection lens of Patent Document 2 is a projection lens for a rear projector, and has a relatively small image circle as compared with the projection lens for a front projector in the present invention. Therefore, although the lens configuration is similar to that of the present invention, in the projection lens configuration for rear projectors disclosed in the document, the “second group rear group” corresponding to the third lens group of the present invention is used. It is possible to configure with 4 sheets. However, in the projection lens for a front projector according to the present invention, the third lens group needs to be composed of five elements in order to realize a large image circle. The above is the difference between Patent Document 2 and the present invention.

  Further, Patent Document 3 does not show a three-lens cemented lens of a negative lens, a positive lens, and a negative lens, and highly corrects axial chromatic aberration and chromatic aberration of magnification, and flare (a phenomenon in which spots spread due to aberration, a so-called phenomenon). The projected image has less “smudge”) and cannot exhibit high resolution.

  As described above, an object of the present invention is to provide a projection lens having a lens configuration characteristic of the third lens group.

  Another object of the present invention is configured by integrally joining three negative, positive, and negative lenses in the order closest to the stop, and the remaining two lenses are positive lenses, and the third lens is the rear group. A series of projection lens types that have a lens structure that is positive for the entire group, can have a large image circle, have a short overall length, a long back focus, and maintain high performance while maintaining a high level of performance. Is to provide a projection lens.

  Examples of the solving means of the present invention for solving the above-described problems are as described in the claims.

  In particular, in the projection lens according to the present invention, in the projection lens composed of three lens groups, the third lens group, which is the rear group arranged in the vicinity of the diaphragm, is composed of five lenses, and is negative and positive in the order closest to the diaphragm. The negative three lenses are integrally joined, the remaining two lenses are positive lenses, and the entire rear third lens group is positive.

  As described above, the projection lens of the present invention is configured by integrally joining three negative, positive, and negative lenses in the order closest to the diaphragm, which is a lens configuration characteristic of the third lens group. The remaining two lenses are positive lenses, and the entire third lens group, which is the rear group, has a positive lens configuration, so that the image circle can be made large, the overall length is short, and the back focus is increased. In addition, a series of projection lens types that are compact and have a small number of sheets can be realized while maintaining performance. Further, by using the lens type of the present invention, it becomes possible to design a projection lens corresponding to a standard angle of view to a wide angle. In addition, the front group also has an effect that may or may not include an aspherical surface.

  The present invention is an improvement of a projection lens composed of three lens groups that are compact and have a small number of sheets.

  According to one embodiment of the present invention, in the projection lens according to the present invention, the third lens group, which is the rear group arranged in the vicinity of the stop, is composed of five lenses, and is negative, positive, Three negative lenses are integrally joined, the remaining two lenses are positive lenses, and the entire rear third lens group is positive.

  According to another embodiment of the present invention, the projection lens according to the present invention includes a first lens group, a second lens group, a diaphragm, and a third lens group in the order closest to the screen, and is located behind the third lens group. Is provided with an image forming element, the first lens group is composed of two first and second lenses, the first lens is a negative lens having a convex large convex on the screen side, and the second lens is a screen ( A negative lens having a double-sided aspheric surface that is convex on the (magnifying) side, and a second lens group is disposed at a distance from the first lens group. The second lens group is composed of a single third lens. The three lenses are positive lenses.

  According to still another embodiment of the present invention, the projection lens according to the present invention includes a first lens group, a second lens group, a stop, and a third lens group in the order closest to the screen. An image forming element is arranged behind the first lens group. The first lens group includes five lenses, the first lens is a positive lens having a large aperture convex toward the screen, and the second lens is a spherical surface convex toward the screen. Negative lens, the third lens is a spherical negative lens, the fourth lens is a spherical negative lens, and the fifth lens is a positive lens convex to the image forming element side. The second lens is spaced from the first lens group. The second lens group includes two lenses. The two lenses are a sixth lens that is a positive lens convex on the image forming element side, and a positive lens that is convex on the screen side. This is the seventh lens.

  According to still another embodiment of the present invention, the projection lens includes a first lens group, a second lens group, a diaphragm, and a third lens group in the order closest to the screen, and there is an image behind the third lens group. The forming element is arranged, the first lens group is composed of three lenses, the first lens is a negative lens having a large aperture convex on the screen side, the second lens is a spherical negative lens convex on the screen side, The third lens is a double-sided aspherical negative lens, and a second lens group is disposed at a distance from the first lens group. The second lens group is composed of two lenses, and these two lenses. Are a fourth lens which is a positive lens convex on the image forming element side and a fifth lens which is a positive lens convex on the screen side.

  According to still another embodiment of the present invention, the projection lens includes a first lens group, a second lens group, a stop, and a third lens group as a rear group in the order closest to the screen. An image forming element is arranged behind the first lens group. The first lens group includes three lenses. The first lens is convex on the screen side and has a large spherical aperture. The second lens is convex on the screen side. The spherical negative lens and the third lens are double-sided aspherical negative lenses, the second lens group is disposed at a distance from the first lens group, and the second lens group consists of two lenses, The two lenses are a fourth lens that is a positive lens convex on the image forming element side and a fifth lens that is a positive lens convex on the screen side.

  According to still another embodiment of the present invention, the projection lens includes a first lens group, a second lens group, a stop, and a third lens group as a rear group in the order closest to the screen. An image forming element is arranged on the rear side. The first lens group includes four lenses. The first lens is convex on the screen side and is a negative aspherical lens having a large aperture. The second lens is on the screen side. A convex aspherical negative lens, the third lens is a spherical negative lens convex to the screen side, the fourth lens is a negative lens, and the second lens group is disposed at a distance from the first lens, The second lens group includes two lenses. These two lenses are a fifth lens that is a positive lens convex to the image forming element side and a sixth lens that is a positive lens convex to the screen side. .

  Embodiments of the present invention will be described below with reference to the drawings.

  The projection lens of the first embodiment of the present invention is a standard field angle lens using an aspherical surface.

  The specifications of the lens are as follows.

1.f = 16.67mm F / 2.4
2. Design wavelength λ = 630nm, 550nm, 460nm
3. Total length 136.53mm
4. Back focus 36.73mm
Including prism with refractive index n = 1.5163 and thickness t = 24mm
5. Image height y '= 10.67mm, half angle of view 33 °
6. L2 is Plastic Lens FIG. 1 shows the lens configuration of the projection lens of Example 1.

The projection lens 1 of Example 1 includes a first lens group G1, a second lens group G2, a diaphragm D, and a third lens group G3 in the order closest to a screen (not shown). An image forming element E is disposed behind the third lens group G3.

  The first lens group G1 includes two lenses, the first lens L1 is a negative lens having a large aperture convex on the screen (enlargement) side, and the second lens L2 is a double-sided aspheric surface convex on the screen (enlargement) side. It is a negative lens.

  A second lens group G2 is disposed at a distance from the first lens group G1. The second lens group G2 includes a single third lens L3, and the third lens L3 is a positive lens. Note that two lenses and a positive lens with an air gap may be collectively considered as the first lens group.

  In the case of Example 1 of the present invention, the first lens group G1, the second lens group G2, and the third lens group G3, which is the rear group, are considered separately.

  A third lens group G3 is disposed behind the diaphragm D, that is, on the image forming element E side. The third lens group G3 is arranged in the order closest to the stop D, the fourth lens L4, which is a negative lens convex on the screen (enlargement) side, the fifth lens L5, which is a biconvex positive lens, and the image forming element E (reduction) side. The lens includes a cemented lens in which three lenses of a sixth lens L6 that is a negative convex lens are cemented, and five lenses of a seventh lens L7 and an eighth lens L8 that are two positive lenses.

  The third lens group G3 includes five lenses as described above, but is a positive lens as a whole.

  The optical path diagram of the projection lens 1 of Example 1 is as shown in FIG.

  2 and 3 show longitudinal aberrations and lateral aberrations of the projection lens of Example 1, respectively. 4 and 5 show the through focus MTF with respect to lateral chromatic aberration and 47 line pair / mm, respectively.

  The lens data of the projection lens 1 of Example 1 is as shown in Table 1. The 18th and 19th surfaces in Table 1 are cover glasses.

The second lens L2 of the first lens group G1 is a lens convex on the screen (enlargement) side and having both aspheric surfaces, and the aspheric coefficients of the two surfaces (third surface and fourth surface) of the second lens L2 are As shown in Table 2. The material is PMMA (nd = 1.49210, vd = 57.90), but other suitable optical plastics can also be used. The definition of an aspherical surface, more precisely, a rotationally symmetric aspherical surface is defined by the following [Equation 1].

Z is the sag amount of the aspherical surface.
X represents the height from the optical axis.
R is the central radius of curvature.
K is the conic coefficient.
A, B, C, and D are 4, 6, 8, and 10th-order aspheric coefficients, respectively.

  The projection lens of the second embodiment of the present invention is a standard field angle lens that does not use an aspherical surface.

  The specifications of the lens are as follows.

1.f = 16.78mm F / 2.4
2. Design wavelength λ = 630nm, 550nm, 460nm
3. Total length 160mm
4. Back focus 35.64mm
Including prism with refractive index n = 1.5163 and thickness t = 24mm
5. Image height y '= 10.67mm, half angle of view 33.11 °
FIG. 6 shows the lens configuration of the projection lens of Example 2.

  The projection lens 11 of Example 2 includes a first lens group G11, a second lens group G12, an aperture D, and a third lens group G13 in the order closest to the screen (not shown). An image forming element E is disposed behind the third lens group G13.

  The first lens group G11 includes five lenses, the first lens L11 is a positive lens having a large aperture convex on the screen (enlargement) side, and the second lens L12 is a spherical negative lens convex on the screen (enlargement) side. The third lens L13 is a spherical meniscus lens, the fourth lens L14 is a double-sided spherical negative lens, and the fifth lens L15 is a positive lens convex on the image forming element E (reduction) side.

  A second lens group G12 is arranged at a distance from the first lens group G11. The second lens group G12 is composed of two lenses. The two lenses are a sixth lens L16, which is a positive lens convex on the image forming element E (reduction) side, and a seventh lens L17, which is a positive lens convex on the screen (enlargement) side.

  A third lens group G3 is disposed behind the stop D, that is, on the image forming element E (reduction) side. The third lens group G13 is an eighth lens L18 that is a negative lens, a ninth lens L19 that is a biconvex positive lens, and a negative lens that is convex on the image forming element E (reduction) side, in the order closest to the aperture stop D. A cemented lens in which three lenses of the tenth lens L20 are cemented, an eleventh lens L21 that is a convex positive lens on the image forming element E (reduction) side, and a positive lens that is convex on the screen (enlargement) side The twelfth lens L22 includes five lenses.

  The third lens group G13 includes five lenses as described above, but is a positive lens as a whole.

  7 and 8 show longitudinal aberrations and lateral aberrations of the projection lens of Example 2, respectively. 9 and 10 show the through focus MTF with respect to the lateral chromatic aberration and 47 line pair / mm, respectively.

The lens data of the projection lens 11 of Example 2 is as shown in Table 3. The 26th surface and the 27th surface in Table 3 are cover glasses.

  The projection lens of the third embodiment of the present invention is a quasi-wide angle lens using an aspherical surface.

  The specifications of the lens are as follows.

1.f = 12.87mm F / 2.4
2. Design wavelength λ = 630nm, 550nm, 460nm
3. Total length 155.77mm
4. Back focus 32.49mm
Including prism with refractive index n = 1.5163 and thickness t = 24mm
5. Image height y '= 10.67mm, half angle of view 40.45 °
6. L23 is Plastic Lens FIG. 11 shows the lens configuration of the projection lens of Example 3.

  The projection lens 21 of Example 3 includes a first lens group G21, a second lens group G22, a diaphragm D, and a third lens group G23 in the order closest to the screen (not shown). An image forming element E (image sensor) is disposed behind the third lens group G23.

  The first lens group G21 includes three lenses. The first lens L21 is a negative lens having a large aperture convex on the screen (enlargement) side, and the second lens L22 is a spherical negative lens convex on the screen (enlargement) side. The third lens L23 is a double-sided aspheric negative lens.

  A second lens group G22 is arranged at a distance from the first lens group G21. The second lens group G22 includes two lenses. The two lenses are a fourth lens L24, which is a positive lens convex on the image forming element E (reduction) side, and a fifth lens L25, which is a positive lens convex on the screen (enlargement) side.

  A third lens group G23 is disposed behind the stop D, that is, on the image forming element E (reduction) side. The third lens group G23 is a sixth lens L26 that is a negative lens, a seventh lens L27 that is a biconvex positive lens, and a negative lens that is convex on the image forming element E (reduction) side, in the order closest to the aperture stop D. A cemented lens in which three lenses of eight lenses L28 are cemented, a ninth lens L29 that is a positive lens convex on the image forming element E (reduction) side, and a first positive lens that is convex on the screen (enlargement) side It consists of 5 lenses of 10 lenses L30.

  As described above, the third lens group G23 includes five lenses, but is a positive lens as a whole.

  12 and 13 show longitudinal aberration and lateral aberration of the projection lens of Example 3, respectively. FIGS. 14 and 15 show the through focus MTF with respect to lateral chromatic aberration and 47 line pair / mm, respectively.

  The lens data of the projection lens 21 of Example 3 is as shown in Table 4. The 22nd surface and the 23rd surface in Table 4 are cover glasses.

The third lens L23 of the first lens group G21 is a lens that is convex on the screen (enlargement) side and has two aspheric surfaces. The aspheric coefficients of the two surfaces (fifth surface and sixth surface) of the third lens L23 are As shown in Table 5. The definition of the aspherical surface, more precisely, the rotationally symmetric aspherical surface is the same as that in the first embodiment. The material is PMMA (nd = 1.49210, vd = 57.90), but other suitable optical plastics can also be used.

  The projection lens of the fourth embodiment of the present invention is a wide-angle projection lens using only one aspherical surface.

  The specifications of the lens are as follows.

1.f = 11.51 mm F / 2.4
2. Design wavelength λ = 630nm, 550nm, 460nm
3. Total length 186.0mm
4. Back focus 32.50mm
Including prism with refractive index n = 1.5163 and thickness t = 24mm
5. Image height y '= 12.11mm, Half angle of view 46.8 °
6. L33 is Plastic Lens FIG. 16 shows the lens configuration of the projection lens of Example 4.

  The projection lens 31 of Example 4 includes a first lens group G31, a second lens group G32, a diaphragm D, and a third lens group G33, which is a rear group, in the order closest to a screen (not shown). An image forming element E is disposed behind the third lens group G33.

  The first lens group G31 is composed of three lenses, the first lens L31 is a negative lens having a large spherical aperture convex on the screen (enlargement) side, and the second lens L32 is a spherical surface convex on the screen (enlargement) side. The negative lens and the third lens L33 are double-sided aspheric negative lenses.

  A second lens group G32 is arranged at a distance from the first lens group G31. The second lens group G33 is composed of two lenses. The two lenses are a fourth lens L34 that is a positive lens convex on the image forming element E (reduction) side and a fifth lens L35 that is a positive lens convex on the screen (enlargement) side.

  A third lens group G33 is disposed behind the stop D, that is, on the image forming element E (reduction) side. The third lens group G33 is a sixth lens L36 that is a negative lens, a seventh lens L37 that is a biconvex positive lens, and a negative lens that is convex on the image forming element E (reduction) side, in the order closest to the stop D. A cemented lens in which three lenses of the eighth lens L38 are cemented, a ninth lens L39 that is a positive lens convex on the image forming element E (reduction) side, and a positive lens that is convex on the screen (enlargement) side The tenth lens L40 includes five lenses.

  The third lens group G33 includes five lenses as described above, but is a positive lens as a whole.

  FIGS. 17 and 18 show longitudinal aberrations and lateral aberrations of the projection lens of Example 4, respectively. FIGS. 19 and 20 show the through-focus MTF for chromatic aberration of magnification and 47 line pair / mm, respectively.

  The lens data of the projection lens 31 of Example 4 is as shown in Table 6.

The third lens L33 of the first lens group G31 is a lens that is convex on the screen (enlargement) side and has two aspheric surfaces. The aspheric coefficients of the two surfaces (fifth surface and sixth surface) of the third lens L33 are As shown in Table 7. The definition of the aspherical surface, more precisely, the rotationally symmetric aspherical surface is the same as that in the first embodiment.

  The projection lens according to the fifth embodiment of the present invention is a super wide-angle lens using two aspheric surfaces.

  The specifications of the lens are as follows.

1.f = 11.41 mm F / 2.4
2. Design wavelength λ = 630nm, 550nm, 460nm
3. Total length 187.95mm
4. Back focus 32.50mm
Including prism with refractive index n = 1.5163 and thickness t = 24mm
5. Image height y '= 12.11mm, Half angle of view 47.1 °
6. L41 and L42 are Plastic Lenses FIG. 21 shows the lens configuration of the projection lens of Example 5.

  The projection lens 41 of Example 5 includes a first lens group G41, a second lens group G42, an aperture D, and a third lens group G43, which is a rear group, in the order closest to a screen (not shown). An image forming element E (image sensor) is disposed behind the third lens group G43.

  The first lens group G41 includes four lenses. The first lens L41 is convex on the screen (enlargement) side and is an aspheric negative lens having a large aperture. The second lens L42 is convex on the screen (enlargement) side and is not A spherical negative lens, the third lens L43 is a spherical negative lens convex on the screen (enlargement) side, and the fourth lens L44 is a negative lens.

  A second lens group G42 is arranged at a distance from the first lens G41. The second lens group G42 includes two lenses. The two lenses are a fifth lens L45, which is a positive lens convex on the image forming element (reduction) side, and a sixth lens 46, which is a positive lens convex on the screen (enlargement) side.

  A third lens group G43 is disposed behind the stop D, that is, on the image forming element E (reduction) side. The third lens group G43 is a seventh lens L47 that is a negative lens, an eighth lens L48 that is a biconvex positive lens, and a negative lens that is convex on the image forming element E (reduction) side, in the order closest to the diaphragm D. The ninth lens L49 is a cemented lens in which three lenses are cemented, a tenth lens L50 that is a positive lens convex on the image forming element E (reduction) side, and a positive lens that is convex on the screen (enlargement) side. The eleventh lens L51 is composed of five lenses.

  The third lens group G43 includes five lenses as described above, but is a positive lens as a whole.

  22 and 23 show longitudinal aberration and lateral aberration of the projection lens of Example 5, respectively. FIGS. 24 and 25 show chromatic aberration of magnification and through focus MTF with respect to 47 line pair / mm, respectively.

  The lens data of the projection lens 41 of Example 5 is as shown in Table 8.

Table 9 shows the aspherical coefficients of the two surfaces (first surface and second surface) of the first lens L41 of the first lens group G41 and the two surfaces (third surface and fourth surface) of the second lens L42. It is shown. The definition of the aspherical surface, more precisely, the rotationally symmetric aspherical surface is the same as that in the first embodiment.

  In the present invention, the first lens group, the second lens group, the stop, and the third lens group as the rear group are arranged in the order close to the screen, and an image forming element is arranged behind the third lens group. The first lens group is composed of four lenses, the first lens is convex on the screen side and is an aspheric negative lens with a large aperture, the second lens is convex on the screen side and is a spherical negative lens, and the third lens is A convex negative aspheric lens on the screen side, the fourth lens is a spherical negative lens, and a second lens group is arranged at a distance from the first lens, and the second lens group is composed of two lenses. These two lenses may be a fifth lens that is a positive lens convex on the image forming element side and a projection lens that is a sixth lens that is a positive lens convex on the screen side.

  Further, in order from the screen, the first lens group, the second lens group, the stop, and the third lens group that is the rear group, an image forming element is disposed behind the third lens group, and the first lens The group consists of four lenses, the first lens is convex on the screen side and is an aspheric negative lens with a large aperture, the second lens is convex on the screen side and is a spherical negative lens, and the third lens is convex on the screen side The spherical negative lens and the fourth lens are aspherical negative lenses, and a second lens group is disposed at a distance from the first lens, and the second lens group is composed of two lenses, These two lenses may be a fifth lens that is a positive lens convex on the image forming element side and a projection lens that is a sixth lens that is a positive lens convex on the screen side.

  As described above, the projection lens of the present invention has a characteristic lens configuration of the third lens group, and is configured by integrally joining three negative, positive, and negative lenses in the order closest to the stop, and the remaining 2 lenses. Since the single lens is a positive lens and the entire third lens group, which is the rear group, has a positive lens configuration, the image circle (imaging surface) can be made large, the overall length is short, and the back focus is increased. In addition, it is possible to realize a series of projection lens types that are compact and have a small number of sheets while maintaining high performance. Further, by using the lens type of the present invention, it becomes possible to design a projection lens corresponding to a standard angle of view to a wide angle. In addition, the front group also has an effect that may or may not include an aspherical surface.

  Note that the first lens group and the second lens group are not limited to the lens groups disclosed in the above-described embodiments, and the third lens group is also a characteristic lens configuration of negative, positive, If the negative three lenses are integrally joined, the remaining two lenses are positive lenses, and the entire third lens group as the rear group has a positive lens configuration, various types can be used. The configuration of can be adopted.

1 shows a lens configuration of a projection lens of Example 1. 2 shows longitudinal aberrations of the projection lens of Example 1. FIG. 2 shows lateral aberrations of the projection lens of Example 1. FIG. The lateral chromatic aberration is shown. The through focus MTF with respect to 47 line pair / mm is shown. 2 shows a lens configuration of a projection lens of Example 2. 10 shows longitudinal aberrations of the projection lens of Example 2. 4 shows lateral aberrations of the projection lens of Example 2. FIG. The lateral chromatic aberration is shown. The through focus MTF with respect to 47 line pair / mm is shown. 5 shows a lens configuration of a projection lens according to Example 3. 10 shows longitudinal aberrations of the projection lens of Example 3. 10 shows lateral aberrations of the projection lens of Example 3. FIG. The lateral chromatic aberration is shown. The through focus MTF with respect to 47 line pair / mm is shown. 10 shows a lens configuration of a projection lens according to Example 4. 10 shows longitudinal aberrations of the projection lens of Example 4. FIG. 10 shows lateral aberrations of the projection lens of Example 4. FIG. The lateral chromatic aberration is shown. The through focus MTF with respect to 47 line pair / mm is shown. 10 shows a lens configuration of a projection lens according to Example 5. 10 shows longitudinal aberrations of the projection lens of Example 5. FIG. 10 shows lateral aberrations of the projection lens of Example 5. FIG. The lateral chromatic aberration is shown. A through focus MTF for 47 line pair / mm is shown. A description of the shift is shown.

Claims (8)

  In the projection lens composed of three lens groups, the third lens group, which is the rear group arranged in the vicinity of the diaphragm, is composed of five lenses, and the three negative, positive, and negative lenses are integrated in the order closest to the diaphragm. A projection lens comprising a cemented structure, the remaining two lenses being positive lenses, and the entire third lens group as a rear group being positive.   The projection lens according to claim 1, wherein three lens groups are arranged so as not to bend the optical path in the middle of the lens system.   The first lens group, the second lens group, the stop, and the third lens group are arranged in order from the screen, and an image forming element is disposed behind the third lens group. The first lens is composed of a first lens and a second lens, the first lens is a negative lens having a large aperture convex on the screen side, and the second lens is a double-sided aspherical negative lens convex on the screen side, spaced from the first lens group. The projection lens according to claim 1, wherein a second lens group is disposed, the second lens group includes one third lens, and the third lens is a positive lens.   The first lens group, the second lens group, the stop, and the third lens group are arranged in the order close to the screen, and an image forming element is disposed behind the third lens group. The first lens is a positive lens having a large aperture convex on the screen side, the second lens is a spherical negative lens convex on the screen side, the third lens is a spherical negative lens, and the fourth lens is a spherical negative lens. The fifth lens is a spherical positive lens convex on the image forming element side, the second lens group is disposed at a distance from the first lens group, and the second lens group is composed of two lenses, 2. The projection according to claim 1, wherein the two lenses are a sixth lens that is a positive lens convex on the image forming element side and a seventh lens that is a negative lens convex on the screen side. lens.   The first lens group, the second lens group, the stop, and the third lens group are arranged in the order close to the screen, and an image forming element is disposed behind the third lens group. The first lens is a negative lens having a large aperture convex on the screen side, the second lens is a spherical negative lens convex on the screen side, the third lens is a double-sided aspheric negative lens, and the first lens group And the second lens group is composed of two lenses, and these two lenses include a fourth lens that is a positive lens convex on the image forming element side. The projection lens according to claim 1, wherein the projection lens is a fifth lens that is a positive lens convex on the screen side.   The first lens group, the second lens group, the stop, and the third lens group as the rear group are arranged in the order close to the screen, and an image forming element is disposed behind the third lens group. The first lens is a negative lens with a large spherical aperture convex on the screen side, the second lens is a spherical negative lens convex on the screen side, and the third lens is a double-sided aspheric negative lens. There is a second lens group that is spaced apart from the first lens group, and the second lens group is composed of two lenses, and these two lenses are positive lenses that are convex on the image forming element side. The projection lens according to claim 1, wherein the fourth lens is a fifth lens that is a positive lens convex on the screen side.   The first lens group, the second lens group, the stop, and the third lens group as the rear group are arranged in the order close to the screen, and an image forming element is disposed behind the third lens group. It consists of four lenses, the first lens is convex on the screen side and aspherical negative lens with a large aperture, the second lens is convex on the screen side and aspherical negative lens, the third lens is convex on the screen side A spherical negative lens and a fourth lens are negative lenses, and a second lens group is disposed at a distance from the first lens. The second lens group is composed of two lenses, and these two lenses are The projection lens according to claim 1, wherein the lens is a fifth lens that is a positive lens convex to the image forming element side and a sixth lens that is a positive lens convex to the screen side.   The first lens group, the second lens group, the stop, and the third lens group as the rear group are arranged in the order close to the screen, and an image forming element is disposed behind the third lens group. It consists of four lenses, the first lens is convex on the screen side and is an aspheric negative lens with a large aperture, and the second to fourth lenses are one aspherical negative lens and two spherical negative lenses. The second lens group is arranged at a distance from the first lens, and the second lens group is composed of two lenses, and these two lenses are positive lenses convex to the image forming element side. The projection lens according to claim 1, wherein the projection lens is a fifth lens and a sixth lens that is formed from a positive lens convex on the screen side.

Images