JPH0313566B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens for a 35 mm single-lens reflex camera that satisfies the range from a semi-wide angle range to a telephoto range. A zoom lens that satisfies the range from a semi-wide-angle lens to a telephoto lens and is highly useful for normal photography has been desired, but in order to design it compactly, it is especially important to use the first group as the focusing section and the variator section. It is necessary to shorten the absolute value of the focal length of the second group, which causes an increase in various aberrations and is extremely difficult to correct. The present invention has a variable focal length range of 35 to 135 m.
m. The objective was to enable a lens with a large aperture of F3.5 class on the wide-angle side, and an extremely compact configuration. The features of the present invention include, in order from the object side, the first group with positive refractive power as the focusing section, the second group with negative refractive power as the variator section, the third group with positive refractive power as the compensator section, and the third group with positive refractive power as the master section. In an optical system, the second group is arranged in order from the object side, in which magnification is varied by relative movement of the first, third, and fourth groups, and focusing is performed by independent movement of the first group. A cemented lens consisting of a negative lens G ₄ with a stronger curvature on the image side, positive and negative elements G ₅ and G ₆ , a negative lens G ₇ with a stronger curvature on the object side, and a positive lens G ₈ with a stronger curvature on the object side. A zoom lens configured to satisfy the following conditions. (1) 0.47<|f/fw|<0.49, f<0 (2) 0.9<-R/f<1.1 (3) 1.5<R6/f<1.7 (4) 2.1<-R8/f<2.3 (5) ) 1.72<N1 (6) 1.65<N4<1.7 (7) 1.8<N5 where f...focal length of the second group fW...shortest focal length of the entire zoom lens system Ri...i-th lens surface of the second group Radius of curvature Ni...Refractive power of the i-th glass material of the second group at the d-line Next, to explain the above characteristics in detail, when the first group has a positive refractive power, the second group has a negative refractive power. is inevitable. The absolute value of the focal length of the second group of the present invention is set to be very short compared to the shortest focal length of the zoom lens system, and is fixed during zooming to eliminate operational errors caused by movement of the second group. Further, the first lens group and the fourth lens group are moved integrally during zooming, and only the third lens group is moved independently. It is easy to infer that this movement method for each lens group is compact when actually assembling the lens, yet it can be easily assembled with high precision, and it will also be effective in reducing costs such as parts processing and assembly man-hours. can. Condition (1) is an appropriate range for the focal length of the second group; if the lower limit is exceeded, it is extremely difficult to correct spherical aberration, especially at the maximum telephoto end, and if the upper limit is exceeded, the objective This deviates from the requirements for compact construction. Condition (2) concerns the lens surface with the strongest divergence in the second group, but if the upper limit is exceeded, the negative distortion that occurs on the wide-angle side becomes large and correction becomes difficult. If the lower limit is exceeded, the curvature of field aberration occurring on the wide-angle side becomes large and difficult to correct. In order to cancel the distortion and field curvature aberration that occur on the wide-angle side, we installed a biconcave lens with a strongly concave surface facing the object side, but condition (3) is the appropriate range of this lens, and if the upper limit is exceeded, the wide-angle side Distortion is further reduced, but at the telephoto end, coma aberration worsens and flare becomes large. If the lower limit is exceeded, significant negative distortion will occur on the wide-angle side, and the curvature of field will also be considerably excessive, and if it exceeds the limit of the appropriate range, it will not be possible to correct these aberrations with other lens surfaces. It's impossible. Spherical aberration is mostly corrected by the third group, but
Fluctuations in spherical aberration due to zooming can be corrected by a convex meniscus lens in which the strongest convex surface on the image side of the second group faces the object side. Condition (4) is necessary for this purpose, and if the lower limit is exceeded, the spherical aberration on the telephoto side will be significantly undervalued.
On the other hand, if it exceeds the upper limit, it will be significantly over,
Since this change in the R8 surface has a large effect on the spherical aberration on the telephoto side, it is impossible to correct this spherical aberration with other lens surfaces outside the range of condition (4). Condition (5) is necessary to reduce field curvature aberration on the wide-angle side, and the light flux at the peripheral angle of view passes through the first lens on the object side of the second group, the farthest position from the optical axis. The higher the refractive index of this lens, the larger the radius of curvature of the lens surface, which has the effect of preventing rapid divergence of the luminous flux. Condition (6) is primarily a condition for lenses that are effective in correcting distortion aberrations, but if this refractive index is high, the Petzval sum becomes large, making it difficult to correct astigmatism. If the lower limit is exceeded, negative distortion will occur significantly on the wide-angle side, and it will be impossible to correct this with other lens surfaces. Condition (7) concerns lenses that are important for correcting spherical aberration on the telephoto side, and this refractive index has a large effect on the shape of spherical aberration. If the lower limit is exceeded, spherical aberration will be insufficiently corrected. Next, examples of the present invention will be shown. fW=36.28, f=-17.256, R2=17.01,
R6=-26.436, R8=38.965, (1) |f/fW|=0.476, (2) -R2/f=0.986, (3) R6/f=1.532, (4) -R8/f=2.258, ( 5) N1=1.726, (6) N4=1.6779, (7) N5=1.80518

[Table] As can be seen from the aberration diagrams in the examples, this is an excellent zoom that maintains excellent imaging performance even when changing the magnification by zooming, and has sufficient imaging performance even when the shooting distance changes. It turns out it's a lens. In the example, G ₁ , G ₂ and G ₁₀ , G ₁₁ are both cemented lenses, but for the purpose of cost reduction, a very small space is provided between each lens, so there is no problem even if they are not cemented. do not have.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram of various aberrations for an object at an infinite distance with the shortest focal length (f = 36.28), and FIG. 3 is a diagram of various aberrations for a close object. Figure 4 is a diagram of various aberrations for an object at infinity with an intermediate focal length (f = 83.60) in the example, Figure 5 is a diagram of various aberrations for a close object, and Figure 6 is
FIG. 7 is a diagram of various aberrations for an object at infinity with the longest focal length (f=132.06), and FIG. 7 is a diagram of various aberrations for an object at a short distance. G ₁ ...G ₁₅ ...Each single lens from the object side, r ₁ ...
r ₂₇ ……Radius of curvature of each single lens, ……Each lens group from the object side.

Claims (1)

[Claims] 1. In order from the object side, a first group with positive refractive power as a focusing section, a second group with negative refractive power as a variator section, a third group with positive refractive power as a compensator section, and a positive group as a master section. In an optical system having a fourth lens group with refractive power, zooming is performed by relative movement of the first, third, and fourth lens groups, and focusing is performed by independent movement of the first lens group, the second group is In order from the side, a negative lens G ₄ having a stronger curvature on the image side, a cemented lens made by cementing positive and negative elements G ₅ and G ₆ , a negative lens G 7 having a stronger curvature on the object side, and a negative lens G ₇ having a stronger curvature on the object side. A zoom lens comprising a positive lens _G8 having the following characteristics: (1) 0.47＜｜f/fw｜＜0.49, f＜0 (2) 0.9＜−R2/f＜1.1 (3) 1.5＜R6/f＜1.7 (4) 2.1＜−R8/f＜2.3 (5 ) 1.72<N1 (6) 1.65<N4<1.7 (7) 1.8<N5 where f...focal length of the second group fW...shortest focal length of the entire zoom lens system Ri...i-th lens surface of the second group Radius of curvature Ni...Refractive power of the i-th glass material d-line of the second group.