JPS6045402B2 - Lens system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bright lens system having an angle of view of 210 to 450, an FN of 02.0 to 1, and a sharpness in which various aberrations are well corrected. The present invention relates to a lens system suitable for use as a lens.

In general, securing image plane properties is an important condition for projection lenses, and for this purpose, the Petzval sum must be 0.3 or less.

If the value exceeds this value, the flatness of the image plane will be lost, and the astigmatic difference will become larger, making it impossible to maintain a balance between the center and the periphery, resulting in a decrease in image quality. The Ernostar type conventionally used as a projection lens has a Pebbal sum of 0.
4 to 0, which is moderate, and it is difficult to reduce this to 0.3 or less. On the other hand, if a Gaussian type lens is used, it is possible to reduce the Petzval sum to 0.3 or less and various aberrations are well corrected. Because of this, it has poor workability and is expensive in terms of cost. The present invention does not use a cemented lens, and has a surface with a gentle radius of curvature of 0,5f or more, so that the Petzval sum is 0, which is similar to the Gaussian type.
．． The objective is to construct a lens system in which the ratio is 1 to 0.25. Although the lens system of the present invention is suitable for use as a projection lens, it goes without saying that it can also be used as an objective lens for a camera. The structural requirements of the present invention are that the first group G is a positive lens, the second group G2 is a rain lens, the third group G3 is a positive lens, and the fourth group G is a positive lens.

This lens system is characterized by having a biconvex lens and a fifth group G5 consisting of a rain lens, which satisfies the following conditions. Mountain + d7 + d9 (1) 0.45 < G3, G4, G
5 axial core thickness D8: axial air gap between D4 and G5 Σd: total length of the lens system R8: radius of curvature of the G5 side surface of G4 R9: curvature radius f of the G4 side surface of G5: focal point of the entire system Distance In the above configuration, condition (1) is for making the Petzval sum good and ensuring image surface properties.

When approaching the upper limit, the Petzval sum becomes smaller, but
On the other hand, the lens system becomes long, and the projection lens tends to lack the amount of peripheral light that is especially necessary. Therefore, it is appropriate to keep it below the upper limit. On the other hand, if it approaches the lower limit,
The Petzval sum becomes large, which deviates from the purpose of the present invention. Therefore, it is appropriate not to divide the lower limit. Condition (2) is provided to balance on-axis and off-axis aberrations.

If the upper limit value is used, the spherical aberration will be over-corrected, the flare of the coma will increase, and the contrast will tend to decrease, so it should be set below the upper limit value. On the other hand, when approaching the lower limit, the spherical aberration becomes under-corrected and the image surface becomes negatively curved.
Flatness tends to be impaired. Therefore, it is appropriate not to divide the lower limit. Condition (3) is for adjusting back focus, spherical aberration, etc.

When approaching the upper limit, the back focus becomes short and spherical aberration tends to be under-corrected, so a burden is placed on other lenses to correct this. Therefore, it is good to exceed the upper limit! Not good. On the other hand, when approaching the lower limit, the sensitivity to machining errors with respect to spherical aberration and coma tends to increase, making machining difficult, so it is appropriate not to exceed the lower limit. Next, specific examples of the present invention are shown in Tables 1 to 5 below!
Shown below.

Examples 1 to 4 are examples in which the lens system of the present invention is used as a projection lens, and Example 5 shows an example in which the lens system of the present invention is applied to an objective lens for a so-called 110 camera. 1, 3, 5, 7, and 9 are lens configuration diagrams of Examples 1 to 5, respectively, and Figures 2, 4, 6, 8, and 10 are aberration diagrams of Examples 1 to 5, respectively.

[Brief explanation of the drawing]

1, 3, 5, 7, and 9 are examples 1 to 9 of the present invention, respectively.
5 and 2, 4, 6, 8, and 10 are aberration diagrams of Examples 1 to 5, respectively. Gl, G2...G,: 1st, 2nd...5th lenses arranged sequentially from the left in the drawing, Rl, r2...
. . . RlO: Radius of curvature of each refracting surface sequentially arranged from the left in the drawing, Dl, d2 . . . D9: Distance on the f-axis between each refractive surface sequentially arranged from the left in the drawing.

Claims (1)

[Claims] 1. Five groups, in order from the object side: a first lens that is a positive lens, a second lens that is a biconcave lens, a third lens that is a positive lens, a fourth lens that is a biconvex lens, and a fifth lens that is a biconcave lens. A lens system consisting of 5 elements and characterized by satisfying the following conditions: 0.45<(d_5+d_7+d_9)/
Σd<0.651.0≦r_8/r_9<2.22.0
<d_8/f<20 where d_5, d_7, d_9: axial core thickness of the third, fourth, and fifth lenses, respectively, d_8: axial air distance between the fourth and fifth lenses Σd: lens Total length of the system r_8: Radius of curvature of the image side surface of the fourth lens r_9: Radius of curvature of the object side surface of the fifth lens f: Focal length of the entire system.