JPH0296107A - Wide angle lens of long back focus - Google Patents

Abstract

PURPOSE:To obtain the lens which has a long back focus and with a bright F-number is obtd. by constituting the lens, successively from an object side, respectively specific 1st lens to 7th lens which respectively satisfy specific conditions. CONSTITUTION:This lens consists, successively from the object side, of the negative 1st lens of a meniscus type the convex face of which is directed to the object side, the positive 2nd lens, the negative 3rd lens of a meniscus type the convex face of which is directed to the object side, the positive 4th lens which has the curvature of the face on the image side than the curvature of the face on the object side, the negative 5th lens, the 6th lens which is a biconvex lens, and the positive 7th lens. The 5th and 6th lens are the combined lens systems. The conditions expressed by equations I to the equation IV are satisfied. In equation I to IV, f123 is the combined focal length from the 1st lens to the 3rd lens, ra is the radius of curvature on the object side face of the 4th lens; rb is the radius of curvature of the image side lens of the 4th lens; f1 is the focal length of the 1st lens; f4 is the focal length of the 4th lens; f is the focal length of the total lens system. The long back focus and the bright F-number are obtd. in this way.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a small, bright lens having a back focus longer than the focal length, particularly an F number of about 1.4, and a photographing lens for small imaging equipment. The present invention relates to a lens suitable for use as a lens.

(Prior Art) With the spread of solid-state imaging devices, there has been a demand for lenses for compact imaging devices that are small, bright, and have a long back focus so as not to impair compatibility with conventional mounts. To meet these demands, lenses based on the same design philosophy as wide-angle photographic lenses have been used, but such lenses have an F2.
Most of the lenses were class 8, and their brightness was insufficient for camera lenses using solid-state image sensors. In addition, bright wide-angle lenses have a large amount of residual aberration, especially spherical aberration and coma flare when the aperture is wide open, and do not fully satisfy the required performance.

(Problems to be Solved by the Invention) The present invention aims to overcome these drawbacks of the prior art and provide a lens with good performance. More specifically, it has a back focus longer than its focal length,
This relates to the configuration of a wide-angle lens with an F number of approximately 1.4.

(Means for solving the problem) The lens system of the present invention includes, in order from the object side, a meniscus-shaped negative first lens with a convex surface facing the object side, a positive second lens, and a positive second lens with a convex surface facing the object side. Consisting of a meniscus-shaped negative third lens, a positive fourth lens whose image side surface has a stronger curvature than the object side surface, a negative fifth lens, a biconvex positive sixth lens, and a positive seventh lens. The fifth and sixth lenses are a lens system composed of seven lenses in six groups and are bonded together, and are characterized by satisfying the following conditions (1) 1.4f<If231<1.9f0. 8
<Engineer><2.O r crystal-rb (3) 2.5f<f4< 3.8f (4)
4.5f<l f, l<6.5f However, f x
2s: Combined focal length r from the first lens to the third lens, : Radius of curvature r of the object side surface of the fourth lens, : Radius of curvature fl of the image side surface of the fourth lens: Focal length of the first lens f4: Focal length of the fourth lens f: Focal length of the entire lens system (effect) In the lens system of the present invention, by giving appropriate negative refractive power to the partial lens system from the first lens to the third lens, , it becomes possible to widen the angle of view of the lens system and obtain a long back focus.

Condition (1) indicates the range of appropriate refractive power to be given to this partial lens system. If it falls below the lower limit, the refractive power of this partial lens system becomes excessively strong, and although a long back focus can be achieved, large negative distortion occurs.
The lens becomes unusable as a camera lens. In addition, in a light beam with a large angle of view, inward coma flare occurs, resulting in a lens with poor imaging performance for low spatial frequencies, making it useless as an imaging lens for cameras using solid-state imaging devices. Become. On the other hand, if the upper limit is exceeded, the refractive power of this partial lens system will become too weak and the back focus will not be long enough, or else the total length of the lens will become considerably long. In addition, if the refractive power of this partial lens system is weak, the degree to which a light beam with a large angle of view is refracted by the composite lens system is small, and as a result, the fourth lens system having a condensing refractive power disposed after it has a small degree of refraction. The light flux will enter the partial lens system consisting of the lens to the seventh lens at a large angle, resulting in a large curvature of field and making it difficult to widen the angle of view.

The fourth lens is a positive lens in which the curvature of the image-side surface is stronger than the curvature of the object-side surface. The shape of the fourth lens is preferably such that the spherical aberration is kept as small as possible with respect to the diverging light beam passing from the first lens through the third lens.

Conditional expression (2) expresses this shape.

If the lower limit of this equation is not reached, the spherical aberration will be excessive, resulting in excessive correction. On the other hand, if it exceeds the upper limit, it will become under-corrected, resulting in insufficient correction.

Conditional expression (3) shows the refractive power of this fourth lens. If the lower limit of this equation is exceeded, that is, if the refractive power of the fourth lens becomes strong, the spherical aberration will be under-corrected. On the other hand, if the upper limit is exceeded, the refractive power of the fourth lens becomes weaker, and the distribution of positive refractive power is biased to the succeeding sixth and seventh lenses, resulting in the occurrence of negative distortion.
become a prisoner. If you want to prevent this, it is necessary to
The refractive power of the partial lens system up to the lens is weakened, the distance between the third lens and the fourth lens is widened, and the total length is increased. Furthermore, it becomes difficult to maintain a long back focus.

Conditional expression (4) concerns the refractive power of the first lens. When this lower limit is reached, the refractive power of the first lens becomes excessively strong, and inward coma flare that occurs in a beam of light with a large angle of view cannot be ignored. If the upper limit is exceeded, the refractive power of the first lens becomes weak, and the inclination of the chief ray incident on the second lens becomes large, making it difficult to correct aberrations over a wide angle of view. If the angle of view of the lens is increased while the upper limit is exceeded, the diameter of the first lens will increase due to the lack of diverging refractive power of the first lens, making it difficult to make the lens compact.

The fifth and sixth lenses are laminated lenses to suppress the occurrence of outward flare at large angles of view.

(Example) Next, examples of this invention will be shown.

Since the light beam passing from the first lens through the fourth lens is greatly expanded compared to the light beam before incidence, it is preferable to provide a diaphragm behind the fourth lens. Providing an aperture here makes it possible to have a large aperture diameter, making it easier and more precise to control the aperture value using an auto iris or the like.

You can also use the existing mount between the lens and camera (
For example, when using C mount, etc., due to lens barrel design,
There may arise a demand for separating the aperture part from the mount part as much as possible.

In the present invention as well, the diaphragm is installed as far forward as possible, but at this time, it is preferable to make the light beam that has passed from the first lens to the fourth lens slightly condensing. By creating a collective light beam (i.e., composite focal length fi234〉0 from the first lens to the fourth lens) in this way, the refractive power of the subsequent lenses (i.e., the fifth, sixth, and seventh lenses) can be adjusted. This makes it possible to set the exit pupil at a far distance, thereby realizing favorable conditions for the solid-state image sensor. The desirable range of the combined focal length 1 f1234 from the first lens to the fourth lens is 4.5 with respect to the focal length laf of the entire lens system.
f < f 1□34<20f (however, f x23
4>O). Below this lower limit, the refractive power burden of the fourth lens becomes large and the spherical aberration is likely to be undervalued. On the other hand, when the upper limit is exceeded, the combined refractive power of the fifth, sixth, and seventh lenses becomes strong, and the exit pupil positions become quite close to each other. In this way, in order to place the exit pupil far away and the diaphragm in front, it is desirable that the combined refractive power of the fifth to seventh lenses be a little weaker than the refractive power of the entire lens system. .

The data of each example is shown below.

The symbols in the table are: ω is the half angle of view, r+ is the radius of curvature of the first surface,
dI is the distance between the first surface and the i+1th surface, n is the refractive index, '1
1.1 represents the Atsube number.

Example 1 Focal length 100mm Fl, 4.4 2ω=68e52' 1 309.485 2 156.085 3 1015.391 4 -573.365 5 265.591 6 93.569 7 -660.133 8 -193.063 9 951.885 10 166.944 11 -381.861 12 252.986 13 1966.673 14 covers 15 glass 1f□2. =172° d.

11.49 45.97 38.58 3.28 11.49 186.66 33.66 158.27 11.49 64.03 3.28 37.76 32.84 9.03 1.72000 1.80518 1.80610 1.77250 1.84666 1.69680 1.51633 50.2 25.4 40.9 49.6 23.8 55.5 55.5 64.1 f4=342. 7 Example 2 focal length 100mm Fl.

2ω=69″40’ i r+ 1 231.609 2 126.144 3 -2836.911 4 -396.528 5 654.691 6 101.050 7 3626.861 8 -218.789 9 3717.536 10 155.097 11 -280.571 12 248.469 1.3 -3469.686 14 cover Q 15 glass f1□3=145.8 d.

20.00 58.32 33.33 3.33 16.66 154.24 36.66 172.03 16.66 66.66 3.33 49.99 49.99 9.17 1.69680 1.83408 1.69680 1.77250 1.84666 1.62299 1.71300 1.51633 55.5 37.2 55.5 49.6 23.8 58.2 53.9 64.1 =268° Example 3 focal length 100 2ω=68″4 r1 1 325.374 2 146.388 3 6910.096 4 -474.838 5 350.400 6 93.153 7 -3864.182 8 -211.554 9 1518.803 10 162.424 11 -298.212 12 246.669 13 -5260.152 14 covers 0 15 glass Q mm 6′ d.

19.70 49.26 32.84 3.28 16.42 165.85 36.13 163.52 16.42 65.68 3.28 49.26 49.26 9.03 Fl.

1.62299 1.83408 1.71300 1.77250 1.84666 1.62299 1.69680 1.51633 58.2 37.2 53.9 49.6 23.8 58.2 55.5 64.1 f engineering ,, = 158.7 f4 = 288.5 - soil = 1.116 1 fl = 446.0a - r b (Effect of the invention) As is clear from the above embodiments and drawings, in the present invention, the long It has achieved back focus, a bright F-number, and good aberration correction, making it possible to provide a lens with excellent performance as a lens for small imaging equipment.

[Brief explanation of drawings]

Figures 1, 2, and 3 show Example 1.2.3, respectively.
The lens sectional view, FIG. 4, FIG. 5, and FIG. 6 are aberration diagrams of Examples 1.2.3, respectively.

Claims (1)

[Claims] In order from the object side: a meniscus-shaped negative first lens with a convex surface facing the object side, a positive second lens, a meniscus-shaped negative third lens with a convex surface facing the object side, and the object. It consists of a positive fourth lens whose surface on the image side has a stronger curvature than the side surface, a negative fifth lens, a biconvex sixth lens, and a positive seventh lens.
, the sixth lens is a lens system composed of seven elements in six groups bonded together, and is a wide-angle lens with a long back focus, characterized in that it satisfies the following conditions. 1.4f<|f_1_2_3|<1.9f 0.8<(r_a+r_b)/(r_a-r_b)<2
．． 02.5f<f_4<3.8f4.5f<|f_1|
<6.5f However, f_1_2_3: Combined focal length from the first lens to the third lens r_a: Radius of curvature of the object-side surface of the fourth lens r_b: Radius of curvature of the image-side surface of the fourth lens f_1: First Focal length of lens f_4: Focal length of fourth lens f: Focal length of entire lens system