JPS587B2 - Bright retro focus lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bright retrofocus lens primarily for use in industrial televisions.

When an automatic diaphragm mechanism is incorporated into an industrial TV lens, the automatic diaphragm mechanism is sometimes placed in front of the focusing mechanism, and in this case, the distance from the diaphragm to the image plane is longer than the focal length of a standard lens. The length is required to be several times as long.

In the present invention, since the distance from the diaphragm to the image plane can be made to be more than twice the focal length, the above-mentioned automatic diaphragm mechanism can be easily incorporated, and even though it has an extremely simple configuration of 5 elements in 4 groups, , Fl,3, and has various aberrations including spherical aberrations well corrected.

The present invention will be described in detail below with reference to the accompanying drawings.As shown in Fig. 1, the present invention has a four-group configuration, in which the concave meniscus lens with its concave surface facing the image side is sequentially arranged from the object side, It is characterized by comprising a second lens that is a convex lens, a third lens that is a cemented concave meniscus lens of a convex lens and a concave lens, and a fourth lens that is a convex lens, and satisfies the following conditions.

(1) 2.5f<, fl, <3.5f(2) 1
．． 5f<r2<2.5f (4) 0.02<r4-r3<0.15(5)
0.5f<d5+d6<0.75f(6) 0.4f
<r7<0.65f However, f: Focal length of the entire system fl: Focal length of the first lens r2: Focal length of the second lens r2. r5: refractive index of the medium of the second lens and the fourth lens, respectively r3. r4: refractive index of the medium of the convex lens and concave lens of the third lens, respectively d5+d6: junction thickness of the third lens r7: radius of curvature of the image side surface of the third lens.

Condition (1) is a condition for correcting distortion aberration and coma aberration. If fl exceeds the upper limit, the focus will become shorter, but if you try to make it longer, the system will become longer.
The diameter of the second lunion becomes larger and becomes less compact.

Furthermore, if fl exceeds the lower limit, it becomes difficult to correct distortion and coma aberration.

Condition (2) relates to correction of spherical aberration and Petzval sum; if f2 exceeds the lower limit, spherical aberration increases and correction becomes difficult.

Also, if f2 exceeds the upper limit, 1. As fl and r7 become larger, the Petzval sum becomes larger.

Condition (3) is for correcting the Petzval sum; if (n2+n5)/2° becomes 1.65 or less, the Petzval sum becomes large, making it difficult to correct the field curvature.

Condition (4) relates to correction of spherical aberration and Petzval sum, and the cemented surface of the third lens is mainly useful for correcting spherical aberration, and the larger the difference n4-n3 between the refractive indexes before and after the cemented surface, the more effective it is. is large, and if it is less than 0.02, there is almost no effect.

However, when n4-n3 becomes 0.15 or more, it becomes difficult to correct the Petzval sum.

Condition (5) is a condition for correcting coma aberration, astigmatism, and distortion in a well-balanced manner.

The object-side surface r5 of the third lens is placed close to the second lens to reduce the occurrence of spherical aberration by sharing positive refractive power, and the surface r7, which has a strong concave surface facing the image side, reduces astigmatism. This helps correct distortion, and the farther the surface is from the aperture, the greater the effect.

The distance between r5 and r7, that is, the junction thickness of the third lens d5+
If d6 is smaller than 0.5f, the above effect will be weakened, making it difficult to correct astigmatism and distortion.

However, if d5+d5 exceeds 0.75f, the comatic aberration generated at r7 increases and becomes difficult to correct.

Condition (6) is for correcting coma aberration, astigmatism, and distortion in a well-balanced manner based on condition (5).
If r7 exceeds the upper limit, it becomes difficult to correct astigmatism and distortion, and if r7 exceeds the lower limit, even if astigmatism and distortion can be corrected, coma aberration increases and balance is lost.

Next, examples of the present invention will be shown.

f=1 Aperture ratio 1:1.32ω=38゜ri
1.4091 d, 9.0919 nl 1.51633 si1
64.1r20.7200 b21.5087 r32.3254 b30.2843 n21.69350 ν253
．． 2r4-2.3254 d40.0123 r50.9321 d50.5208 n31.72000 Shi343
．． 7r6-0.9321 d60.1225 n41.75520 Shi427
．． 5r70.5291 d70.1391 r81.0050 d80.1764 n51.69350 ν553
．． 2r9-18.4102 f1=-2,9872 f2= 1.7196 Distance from aperture to image plane 2.26 Third-order aberration coefficient I of the example ■ ■ P ■10.0
8030.03770.01770.24170.12
172-1.38450.3787-0.1036-0
．． 47290.157730.52200.44700
．． 38270.17610.478641.0236-
0.34940.11920.1761-0.1008
50.03090.02840.02610.4491
0.43636 -0.3815-0.0601-0.
0095-0.0125-0.00357-0.101
6-0.1618-0.2577-0.8133-1.
70578-0.0086-0.0396-0.182
20.40751.037590.4794 -0.2
226-0.10340.0222-0.0583Σ
0.26000.05830.09610.1739
0.3635

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is an aberration curve diagram of spherical aberration, 08C1 astigmatism, and distortion aberration of the same embodiment.

Claims (1)

[Claims] 1. Sequentially from the object side, the first lens of a concave meniscus lens with its concave surface facing the image side, the second lens of a biconvex lens, the third lens of a cemented concave meniscus lens of a convex lens and a concave lens, and the third lens of a convex lens. A bright retrofocus lens consisting of four lenses and satisfying the following conditions. (1) 2.5f<, fl, <3.5f(2) 1
．． 5f<r2<2.5f (4) 0.02<r4-r3<0.15(5)
0.5f<d5+d6<0.75f(6) 0.4f
<r7<0.65f However, f: Focal length of the entire system fl: Focal length of the first lens r2: Focal length of the second lens r2. r5: refractive index of the medium of the second lens and the fourth lens, respectively r3. n4 = refractive index of the medium of the convex lens and concave lens of the third lens, respectively d5+d6: junction thickness of the third lens r7: radius of curvature of the image side surface of the third lens.