JPS587970B2 - Maeshibori Daikokei Lens - Google Patents

Description

[Detailed description of the invention] The present invention relates to a lens having an aperture provided in front of the lens system.

In a normal photographic lens, a diaphragm is installed in a space within the lens structure, and both the entrance pupil and exit pupil are located inside the lens system, but depending on the photographic device, the diaphragm may be placed outside the lens system. required.

For example, when a lens system is built into a camera body, it is necessary to provide an aperture, a shutter, etc. in front of the lens system for mechanical reasons or for reasons of low cost.

However, such a lens system has a problem in that the lens diameter of the rear group becomes large.

Furthermore, it is difficult to balance axial aberrations and off-axis aberrations, and this is particularly difficult when increasing the aperture.

An object of the present invention is to obtain a lens with a large aperture front aperture having a brightness of F1.2 or more and an angle of view of about 43 degrees, and with good aberration correction.

In order to achieve the above object, the features of the present invention are as follows:
The group is a positive single lens, the 2nd group is a biconcave single lens, and at least two of the 2nd, 2nd, and V groups have a cemented or separated two-lens configuration, and the first and The final surfaces are both concave toward the object side, the first surfaces of groups ① and V are convex toward the object side, each has a positive composite refractive power, and the diaphragm is placed in front of group I. N1: refractive index of the I-th group, D1, D2, D3, D4: first and second from the front, respectively.
, 3rd and 4th on-axis spacing, ΣD=sum of on-axis spacing from group I to group ■ (=D1
+D2+D3+D4), f: composite focal length of the entire system, R3, R4, R5: 3rd, 4th, 5th from the front, respectively
Radius of curvature of the th refractive surface, R f, R r: Radius of curvature of the first surface and final surface of group V, respectively; R f, R r: Radius of curvature of the first surface and final surface of group V, respectively. radius of curvature, νf, νr: Atsube numbers of the front and rear lenses in the case of a cemented or separated two-lens configuration in groups Ⅰ and V, respectively, where: (1) 1.6< The following conditions are given: N1 (2) 0.3f<ΣD<1.3f (6) 15<|νf−νr|

Condition (1) in the present invention is that in the above lens configuration,
This is necessary to correct aberrations, especially astigmatism, of a lens that has a large aperture with brightness of F1.2 or higher and an angle of view of approximately 43°.

Since the composite refractive power of the second group is relatively strong, if the lower limit of condition (1) is exceeded, it becomes difficult to sufficiently correct the Petzval sum of the entire system.

Furthermore, if the lower limit of condition (1) is exceeded, the spherical aberration generated in the I group cannot be fully corrected in the II group, and off-axis aberrations, especially the flare of the spherical beam, increase, making it impossible to increase the aperture. Become.

Next, condition (2) relates to the sum ΣD of the on-axis distances from the I-th group to the II-th group, and when this condition is violated, it becomes difficult to obtain a balance between on-axis and off-axis aberrations.

In particular, when the upper limit is exceeded, the lens diameter of the rear group increases significantly,
Since the off-axis light beam passes through the peripheral edge of the lens, high-order aberration coefficients increase, resulting in a lens that is extremely sensitive to errors and extremely difficult to manufacture.

If the lower limit is exceeded, the width of the peripheral beam increases, making it difficult to correct the lower part of the meridional beam especially in transverse aberrations in the open state.

On the other hand, condition (3) is related to the radius of curvature of the negative single lens in the second group, and is necessary to obtain a good balance between spherical aberration and astigmatism. When the occurrence of aberrations and comatic aberrations increases and exceeds the upper limit, it becomes difficult to effectively correct astigmatism and distortion, in particular.

R3 of the biconcave lens in the Ⅰ group has the effect of effectively correcting the spherical aberration mainly generated by the positive lens in the I group, and R4 is effective in correcting the aberration of off-axis light beams, especially astigmatism. .

Furthermore, condition (4) relates to an air lens consisting of the rear surface R4 of the ■th group and the first surface R5 of the ■th group. This is necessary to properly correct distortion without increasing it.

Condition (5) relates to the pending shapes of the first and final surfaces of the 2nd and vth groups, and is necessary to correct the aberrations occurring up to the 2nd group in a well-balanced manner.

For example, within this range of conditions, it is possible to satisfactorily correct spherical aberration, coma aberration, etc. that occur in R2, R3, and R4 and cannot be sufficiently corrected.

If the value is below the limit value of this condition, it is not only difficult to correct spherical aberration, comatic aberration, etc., but also distortion and astigmatism may occur, which is disadvantageous.

Condition (6) relates to the dispersion value of the glass in the case of a cemented or separated two-lens structure in the above-mentioned groups (1) and (V).

The refractive power of the cemented surface and the air lens formed by separation in the ① and Vth groups are both negative, and their main purpose is achromatism.

Therefore, if this condition is not met, chromatic aberration, especially lateral chromatic aberration, remains unavoidable.

If this condition is exceeded and chromatic aberration is corrected by strengthening the refractive power of the cemented surface, not only coma aberration will remain, but
This is inconvenient because astigmatism occurs.

Next, specific examples of the present invention will be shown.

(3) The configuration diagrams of Examples 1, 2, 3.4 above are
, shown in Figure 1.

In Examples 1, 2, 3, and 4, R1, R2, R3... are the radius of curvature of the refractive surface of the lens system in FIGS. 1, 3, 5, and 7, and D1, D2, D3...
represents the axial spacing between the respective refractive surfaces, and Nl, N2, N3... and ν1, ν2, ν3... respectively represent the refractive index and Abbe number of the lens system from the front.

Example 1 shows the case where the No. 1 and No. 3 groups are joined, Example 2 shows the case where the No. 1 concave and No. 2 groups are joined, and Example 3 shows the case where the No. 1 and No. V groups are joined. .

In general, it is possible to sufficiently correct aberrations, especially chromatic aberrations, even if the junction is separated, and Example 4 is shown as an example thereof.

Embodiment 4 is obtained by separating the junctions of group ① of Embodiment 3.

2nd, 4th, 6th and 8th are the above embodiments 1 and 2, respectively.
, 3.4 is shown.

As described above, the present invention is compact and enables good correction of various aberrations, regardless of the front diaphragm and the large aperture lens with brightness of F1, F2 or more.

[Brief explanation of drawings]

1, 3, 5, and 7 are examples 1, 2, and 3, respectively.
．． 4, the second, fourth, sixth, and eighth are aberration diagrams of Examples 1, 2, and 3.4, respectively. ■・・・Group ■, ■・・・Group ■, ■・・
...Group ■, ■...Group ■, ■...
-Group V.

Claims (1)

[Scope of Claims] 1. From the front, the first group is a positive single lens, the (■) group is a biconcave single lens, and at least two of the No. (2), No. (2), and No. V groups
One is a cemented or separated two-lens structure, and the first and final surfaces of the second group are both concave toward the object side, and the second and v groups each have a positive composite refractive power, and the aperture is the I group. N1: refractive index of the I-th group, D1, D2, D3, D4: first and second from the front, respectively.
, 3rd and 4th on-axis surface spacing, ΣD: Sum of axial surface spacings of the pieces from the I group (=D1+D
2+D3+D4) f: Synthetic focal length of the entire system, R3, R4, R5: Radius of curvature of the third, fourth, and fifth refractive surfaces from the front, R f, R r: First surface of the group II, respectively. and the radius of curvature of the final surface, RVf, RVr: radius of curvature of the first surface and final surface of the V group, respectively, νf, νr: the radius of curvature of the cemented or separated two-lens structure in the V group, respectively. The Appe numbers of the front and rear lenses in the case, satisfy the following conditions: (1) 1.6<N1 (2) 0.3f<ΣD<1.3f (6) 15<|νf−νr| Front aperture dog aperture lens.