JPS5820010B2 - Compact, large-diameter semi-wide-angle lens - Google Patents

Description

[Detailed Description of the Invention] Recent wide-angle lenses have developed toward a wider angle of view.
The peak of necessity has shifted from the conventional view angle of 62 to 63 degrees to around 75 degrees.

A normal standard lens normally has an angle of view of up to about 46 degrees, but according to the above-mentioned trend, a standard lens with an angle of view of more than 50 degrees will be required.

Based on this fact, the present invention relates to a semi-wide-angle lens that aims to widen the angle of a small standard lens.

First, to explain the configuration, the first lens is a negative meniscus lens with a convex surface facing the object side, the second lens is a positive lens, and the third lens is a negative meniscus lens with a convex surface facing the object side.
The lens is a positive or negative meniscus lens with a convex surface facing the object side, the 4th lens is a biconcave lens, the 5th lens is a positive meniscus lens with a concave surface facing the object side, and the 6th lens is a biconvex lens. It is a lens composed of two elements.

The codes are defined as follows and their characteristics are listed.

F: Composite focal length Fl...1: Composite focal length n1 up to the i-th lens
: d-1ine refractive index νi of the first lens: Abbe number dj of the first lens: j-th lens interval or lens thickness Fi: focal length ω of the first lens: half angle of view I will explain my position.

Condition (1) is a condition for obtaining the required back focus while keeping the lens system compact.

That is, if IFll is larger than □, the required 0.
35 In order to obtain back focus, d2 must be increased, which is not desirable in terms of miniaturization.

Also, when l F,l is smaller than □, 0.55 is advantageous for obtaining the required back focus, but the second. This is undesirable because the burden on the third lens increases, causing a decrease in the sum of the perapals and worsening of various aberrations, and the burden of aberration correction on the rear group increases.

Condition (2) is the second condition based on condition (1). This determines the positive power of the third lens, and indicates the power required to properly correct chromatic aberration and maintain the aberration balance in the front group.

If Fl-2-3 is larger than □0.45, it is necessary to appropriately under-correct up to the third lens in order to properly maintain the chromatic aberration of the front group up to the third lens. The Abbe number of the third lens must be made extremely small, which is undesirable because it has a drastic effect on the chromatic aberration of magnification.

If Fl-2,3 is 0.75 smaller than □, this is an advantageous condition for correcting chromatic aberration of magnification, but it is likely to cause a negative effect on various aberrations including coma aberration.

Furthermore, the perabaal sum decreases, making it difficult to obtain the desired semi-wide-angle lens.

Condition (3) indicates the relationship between Abbe's number and power for correcting chromatic aberration in relation to conditions (1) and (2), and when it is thicker than the upper limit of 0.9, the chromatic aberration up to the 6th surface is Since the lens is under-corrected, it tends to be difficult to keep the rear group within a short range and achieve good correction of chromatic aberration.

If it is smaller than 0.15 for correspondence, even if a glass material with a small Abbe number is used for the positive lens, there will be too little chromatic aberration that is not corrected as intended, so it is not appropriate to make improvements at intervals, etc.

Condition (4) is a condition that defines downsizing.

If it is smaller than the lower limit of 0.65F, the lens system can be made smaller, but it becomes necessary to reduce the focal length of each lens, which increases various aberrations, which is not preferable.
If it is larger than F, the lens system will become too large to achieve the objective.

Condition (5) is a condition regarding correction of lateral chromatic aberration.

If it is larger than 27, it is advantageous for correcting chromatic aberration, but if a general optical lens is used, increasing the Atsube number of the positive lens will decrease the refractive index, so it is difficult to obtain the required back focus and still Spherical aberration cannot be maintained well.

Furthermore, if the Abbe number of the negative lens is decreased, the refractive index increases, which is not preferable because it results in an increase in the Perapart sum.

Further, if it is smaller than 17, it becomes difficult to correct the insufficient amount of chromatic aberration occurring in the front group, which is not preferable.

Condition (6) determines the power of the third lens.
IF51 is smaller than 03 and it is considered to be effective in correcting aberrations of obliquely incident light, and it is convenient for aberration correction because the position where it exits from the glass material to the air surface and the refractive power can be changed appropriately. .

Condition (7) is a condition that indicates the purpose and characteristics of this lens system.
This objective can be achieved by arranging a negative lens in the second lens, obtaining the desired back focus, and appropriately changing and reducing the incident angle after the second lens.

That is, when d2 is thicker than 0.1F, more back focus than intended is provided, which is not advantageous for aiming at miniaturization.

If it is smaller than 0.05F, the distance between the second and third surfaces will be narrow due to the entrance pupil, and it may be difficult to make a wide-angle lens. It is not appropriate to place it in Luns because it would lose its meaning.

Next, examples will be shown. Example I F=100. Aperture ratio 1:2.0. ω-25,5°r11
72.23 d12.61 n1/ν□1.54814
/45.8r2 71.59 d27.43

[Brief explanation of the drawing]

Figure 1 is a lens configuration diagram in Example 1, Figure 2 is an aberration curve diagram in Example 1, Figure 3 is a lens configuration diagram in Example 2, and Figure 4 is Example 2. Aberration curve diagram at
FIG. 5 is a lens configuration diagram in Example 3, and FIG. 6 is an aberration curve diagram in Example 3.

Claims (1)

[Claims] 1. The first lens is a negative meniscus lens with a convex surface facing the object side, the second lens is a positive lens, the third lens is a positive or negative meniscus lens with a convex surface facing the object side, and the fourth lens is a negative meniscus lens with a convex surface facing the object side. 6 groups consisting of a concave lens, the 5th lens is a positive meniscus lens with its concave surface facing the object side, and the 6th lens is a biconvex lens.
A small, large-aperture, semi-wide-angle lens with excellent performance that satisfies the following conditions among lens elements. (7) 0. Q 5 F<d2< 0. IF However, the signs are determined as follows. F: Composite focal length Fl...i: Composite focal length νi up to the first lens
: Atsube number dJ of the first lens: j-th lens interval or lens thickness Fi: focal length of the i-th lens