JPS6213649B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the improvement of a retrofocus type wide-angle lens, and its purpose is to provide a retrofocus type ultra-wide-angle lens in which each aberration is well corrected despite its simple configuration and compact shape. It is not intended to be provided. As is well known, improvements and developments have been made in recent years to make retrofocus wide-angle lenses larger in diameter or ultra-wide-angle, and although the progress and development seems to be progressing rapidly, when viewed from the point of view of miniaturization, there is still little progress. The situation was far from satisfactory. Although there are currently no lenses that combine the three elements of large aperture, ultra-wide angle, and compact size, they still have a large number of lens components, and this leaves considerable problems in manufacturing and adjustment. There is. In view of the above-mentioned current situation, the present invention has been proposed to provide four front groups of a conventionally known lens system: positive, negative, negative, and negative.
We started improving the retro-type wide-angle lens, which has a total of 8 groups: positive, negative, positive, and rear groups, and despite its simple configuration of 9 elements in 8 groups, it has a back focus f _B of 1.6 f or more. However, the aperture and angle of view with an FNo. of about 2.8 is 92
This makes it possible to provide an ultra-wide-angle lens that is extremely compact and has good performance.The present invention will be explained in detail below with reference to the illustrated embodiments. First, as is clear from FIGS. 1 and 3, which show the basic configuration of the retrofocus type wide-angle lens according to the present invention, when viewed from the object world side, the first group L ₁ includes a A positive meniscus single lens l ₁ with a convex surface with a large curvature facing toward the direction, a second group L ₂ and a third group L ₃ ,
In addition, the fourth group _L4 includes negative meniscus single lenses _l2 , _l3 , each having a concave surface with a large curvature facing the image field side.
L ₄ is placed as the front group, the fifth group L ₅ is a biconvex positive single lens L ₅ with a convex surface with a large curvature facing the object world side, and the sixth group L ₆ is a positive single lens L 5 with a convex surface with a large curvature facing the object field side. The overall negative lens is cemented or divided by _a positive lens _L6 with a convex surface with a large curvature and a _biconcave negative lens _L7 . The lens system consists of 9 elements in 8 groups, with positive meniscus single lenses l ₈ and l ₉ with concave surfaces facing each other as the rear group, and (1) 1.8f < Σd < 2.05f (2) (I) ) 0.30f＜d ₄ +d ₆ +d ₈ ＜0.42f (b) 0.6f＜｜f ₁ , ₂ , ₃ , ₄ ｜ ＜0.7f, f ₁ , ₂ , ₃ , ₄ ＜0 (3) 1.68＜n ₂ +n ₃ +n ₄ /3<1.74 (4) 0.8f< f ₅ <1.2f (5) 1.3f< r ₁₃ <2.2f (6) 1.67<n ₈ +n ₉ /2<1.73 (7) (a) 43 <ν ₂ +ν ₃ +ν ₄ /3<53 (b) 53< ν ₆ <65 However, f: Combined focal length of the entire lens system Σd: Total axial thickness of each lens or axial air spacing d ₄ , d ₆ , d ₈ ; lenses l ₂ and l ₃ , lenses l ₃ and l ₄ ,
Air distance on each axis of lenses l ₄ and l ₅ f ₁ , ₂ , ₃ , ₄ ; Combined focal length of lenses l ₁ , l ₂ , l ₃ , l ₄ f ₅ ; Lens l ₅ in the fifth group L ₅ Single focal length r ₁₃ ; Radius of curvature of the image field side surface of lens _{l 7 in} sixth group L 6 n ₂ , n ₃ , n ₄ , n ₈ , n ₉ ; Each lens l ₂ , l ₃ , l ₄ ,
Refractive index for the d-line of the glass with composition l ₈ , l ₉ ν ₂ , ν ₃ , ν ₄ , ν ₆ ; Each lens l ₂ ,
It simultaneously satisfies the conditions such as the Abbe number of the composition glass of l ₃ , l ₄ , and l ₆ , and the back focus is 1.6 f or more, the F number is approximately 2.8, and the angle of view is approximately
It is a retrofocus wide-angle lens that is unique in that it has an angle of 92 degrees. Hereinafter, the technical background of each of the above-mentioned conditions that enabled the purpose of the present invention to be achieved and the technical significance of these conditions will be explained in detail. In the present invention, first, as is clear from the condition (1),
For a lens system with an FNo. of 2.8 and an angle of view of 92 degrees, the prerequisite is that it has an extremely short overall length. Therefore, when this condition (1) is satisfied, compactness of the lens system can be achieved not only in the length direction but also in the radial direction, particularly in the diameter of the front lens. Therefore, the upper limit of this condition (1) can be said to be the limit value for achieving the original intention of the present invention. However, beyond that lower limit Σd
A decrease in FNo. of 2.8 results in an increase in the refractive power of each single lens.
It becomes impossible to maintain the caliber of Condition (2) is a basic condition for creating an ultra-compact shape, and as in condition (a), in order to maintain a long back focus f _B , the second group in the front group is
L ₂ , each negative single lens of the third group L ₃ and the fourth group L ₄
The air intervals immediately after l ₂ , l ₃ , and l ₄ are set extremely short, and the front group retro system is designed so that even with this short air interval, the long back focus f _B intended by the present invention can be obtained. Condition (b) is that the composite refractive power has a fairly strong negative value. Therefore, the upper limit of condition (a) is the one that suppresses the air gap immediately after each of the above-mentioned negative single lenses l ₂ , l ₃ , and l ₄ from increasing in order to achieve the compactness that the present invention intended from the beginning. The upper limit of condition (b) is also related to the upper limit of condition (a) and is the limit value of negative refractive power at which the required back focus f _B can be obtained without increasing the front group air gap. However, for both conditions (a) and (b), even if the shape becomes smaller beyond the lower limit, the increase in the refractive power of each single lens will cause excessive spherical aberration, which occurs in the retro system in general. , residual excessive negative distortion cannot be corrected by each lens in the rear group. Condition (3) is the second group in the previous group according to condition (2).
Each single lens l ₂ , l ₃ , l ₄ of L ₂ , third group L ₃ , and fourth group L ₄
Each single lens with strong negative refractive power l ₂ , l ₃ ,
By giving l ₄ as large a refractive index as possible and increasing the radius of curvature of the concave surfaces facing the image field side of each of these single lenses l ₂ , l ₃ , and l ₄ , positively acting spherical aberration due to each of these surfaces was calculated. , and attempts to suppress excessive high-order aberrations such as coma aberration and distortion aberration, which act negatively. Therefore, the lower limit of this condition (3) is the limit value for obtaining the above effect, and exceeding the upper limit,
Even if the refractive index of these negative lenses becomes too large, the Petzval sum ΣP of each of these negative lenses l ₂ , l ₃ , l ₄ increases, causing the curvature of field to become negative,
In addition to the conditions following condition (3), corrections are not possible due to other conditions. Condition (4) gives a fairly strong positive refractive power to the positive single lens _l5 of the fifth group _L5 , and eliminates the various effects caused by the negative refractive power in the front group according to condition (2) above. It strongly corrects aberrations, and its upper limit is
This is the limit value for obtaining those effects. If the refractive power of the positive single lens _l5 in the fifth group becomes too strong, exceeding the lower limit of condition (4), the higher-order spherical aberration will become excessively negative, and it will be difficult to balance it with other aberrations. Correction on the vine is impossible even in other places. Condition (5) is to correct the spherical aberration that is slightly under-corrected due to condition (4) above, and to properly correct the distortion aberration in the rear part of the lens system. The radius of curvature of the image field side surface of negative lens l ₇ in ₆ is given relatively strong. Therefore, the upper limit is the limit value for obtaining the above-mentioned effects, and is also for preventing loss of back focus f _B due to excessive length _. If the radius of curvature r ₁₃ of the surface on the image field side becomes too strong,
Due to the occurrence of positive higher-order spherical aberration, it becomes difficult to obtain an aperture of approximately FNo. 2.8. Condition (6) is that the seventh lens group L ₇ , which is located at the rearmost part of the lens system, should be placed at the rear of the lens system in order to maximize the prevention of negative deterioration of spherical aberration and meridional curvature of field in the rear part of the lens system.
It is desirable to give the positive lens group of the eighth group _L8 as large a refractive index as possible, and the lower limit is the limit of its effectiveness. In addition, in order to satisfy the achromatic condition for the rear part of the lens system, the seventh lens group L ₇ and the eighth lens group
The larger the Atsbe number of _L8 , the better. However, the Atsube number that satisfies the achromatic condition is large,
Moreover, usable glass having a high refractive index is limited, and the upper limit is the above-mentioned limit value of usable glass. Therefore, a usable glass having a refractive index larger than the upper limit of (6) does not have an Abbe number that satisfies the achromatic condition, and chromatic aberration cannot be corrected. Condition (7) is a chromatic aberration correction condition necessary to satisfy and promote each of the conditions (1) to (6) above. Condition (a) in condition (7) is the appropriate regulation value for the Atsube number for the negative lens group in the front group when correcting the chromatic aberration of the entire lens system while also correcting the chromatic aberration of magnification. be. If the upper limit of (a) is exceeded and the Atsube number of the negative lens group in the front group becomes too large, resulting in insufficient axial color correction, this must be compensated for by the positive lens _l1 in the first group _L1 . It disappears. However, since there is a limit to increasing the Atsube number of the positive lens l ₁ of the first group L ₁ due to the relationship with the refractive index of the lens l ₁ , the overall color correction becomes impossible. On the other hand, contrary to the above, if the lower limit is exceeded and the axial color becomes overcorrected, and an attempt is made to compensate by reducing the Atsube number of the positive lens l ₁ , the chromatic aberration of higher order magnification due to the lens l ₁ will deteriorate. becomes large, which is not desirable. In addition, the condition (b) is that the positive lens _l6 Abbe number of the sixth group _L6 is given as large as possible in order to strongly correct the color of the positive component in the rear part of the lens system. (6)Fostering the conditions for
It has the role of increasing the refractive index of the seventh group _L7 and the eighth group _L8 positive lenses _l8 and _l9 . The lower limit of condition (b) is a limit value to ensure the above effect. In order to prevent negative deterioration of spherical aberration and meridional curvature of field in the rear portion of the lens system, it is desirable that the refractive index of l ₆ be as large as possible. However, there are a limited number of usable glasses that have a large refractive index and a large Abbe number that can prevent the deterioration of the spherical aberration and meridional curvature of field due to l ₆ , and the upper limit is the above-mentioned usable glasses. This is the limit value. Therefore, a usable glass with an Abbe number larger than the upper limit of (b) does not have the large refractive index necessary to prevent spherical aberration and meridional curvature of field from deteriorating to negative, and the spherical aberration , it is not possible to prevent negative deterioration of meridional field curvature. Next, specific examples of a retrofocus type wide-angle lens having the basic configuration according to the present invention shown in FIG. 1 will be referred to as a first example and a second example, and the present invention shown in FIG. A specific example of a retrofocus type wide-angle lens having the basic configuration according to the above will be described as a third example.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a retrofocus type wide-angle lens according to the present invention, FIG. 2 is a retrofocus type wide-angle lens having the basic configuration shown in FIG. For example, B is each aberration curve diagram of the second embodiment, FIG. 3 is another basic configuration diagram of the retrofocus type wide-angle lens according to the present invention, and FIG. 4 is the basic configuration shown in FIG. 3. FIG. 7 is a diagram showing aberration curves of a third embodiment of the retrofocus wide-angle lens provided with the lens. In Figures 1 and 3, L ₁ , L ₂ , ..., L ₈ ...the first lens constituting the lens system
group, second group, ..., eighth group, l ₁ , l ₂ , ..., l ₉ ...lenses constituting each group of the lens system, in Fig. 1, r ₁ , r ₂ , ..., r ₁₇ ... objects Each lens viewed from the field side
Radius of curvature of l ₁ , l ₂ , ..., l ₉ , d ₁ , d ₂ , ..., d ₁₆ ... On-axis thickness of each lens l ₁ , l ₂ , ..., l ₉ viewed from the object world side, or axis Upper air distance, In Fig. 3, r ₁ , r ₂ ,..., r' ₁₁ ,..., r ₁₇ ... radius of curvature of each lens l ₁ , l ₂ ,..., l ₉ viewed in order from the object world side, d ₁ ,d ₂ ,
…, d ₁₇ … Each lens l ₁ , l ₂ , viewed from the object world side,
..., l ₉ axial thickness or axial air spacing.

Claims (1)

[Claims] 1. Viewed in order from the object world side, the first group L ₁ includes a positive meniscus single lens l ₁ with a convex surface with a large curvature facing the object world side, the second group L ₂ and the third group L ₃ , and the fourth group _L4 has negative meniscus single lenses _l2 , _l3 , and _l4 , each with a concave surface with a large curvature facing the image field side, to form the front group, and the _fifth group L5 has is a biconvex positive single lens l ₅ with a convex surface with a large curvature facing the object world side, and the sixth group L ₆ has a positive lens l ₆ with a convex surface with a large curvature facing the image field side and a biconcave negative lens. The seventh group _L7 and the eighth group _L8 each have positive meniscus single lenses _l8 and _{l9 with} their concave surfaces facing the object world side. (1) 1.8f<Σd<2.05f (2) (A) 0.30f<d ₄ +d ₆ +d ₈ <0.42f (B) 0.6f<| f ₁ , ₂ , ₃ , ₄ | <0.7f, f ₁ , ₂ , ₃ , ₄ <0 (3) 1.68<n ₂ +n ₃ +n ₄ /3<1.74 (4) 0.8f<f ₅ <1.2f ( 5) 1.3f＜r ₁₃ ＜2.2f (6) 1.67＜n ₈ +n ₉ /2＜1.73 (7) (a) 43＜y ₂ +y 3 +y ₄ / ₃ ＜53 (b) 53＜y ₆ ＜65 However, f: composite focal length of the entire lens system Σd: axial thickness of each lens or total axial air spacing d ₄ , d ₆ , d ₈ ; lenses l ₂ and l ₃ ., lenses l ₃ and l _Four ,
Air distance on each axis of lenses l ₄ and l ₅ f ₁ , ₂ , ₃ , ₄ ; Combined focal length of lenses l ₁ , l ₂ , l ₃ , l ₄ f ₅ ; Lens l ₅ in the fifth group L ₅ Single focal length r ₁₃ ; Radius of curvature of the image field side surface of lens _{l 7 in} sixth group L 6 n ₂ , n ₃ , n ₄ , n ₈ , n ₉ ; Each lens l ₂ , l ₃ , l ₄ ,
The refractive index for the d-line of the glasses with the compositions l ₈ and l ₉ is y ₂ , y ₃ , ₄ , y ₆ ; the conditions of the Abbe number of the glasses with the compositions l ₂ , l ₃ , l ₄ , and l ₆ of each lens are simultaneously satisfied. And the back focus is 1.6f or more, the F number is about 2.8, and the angle of view is about 92
A retrofocus wide-angle lens that is characterized by its .