JPS63318511A - Lens for water-proof camera - Google Patents

Abstract

PURPOSE:To shorten the whole length of a lens and to simplify the constitution of the lens by arranging a water-proof glass consisting of a positive lens turning its convex face to the object side and a main lens having positive refractive force and capable of being moved in the optical axis direction so as to be focused successively from the object side. CONSTITUTION:The water-proof glass Ga consisting of the positive lens turning its convex face to the object side is watertightly and integrally held by a water- proof glass holder 12 and arranged on the image side of the glass Ga and the main lens GM having positive refractive force is held by a mirror barrel 16. The mirror barrel 16 is held by a shutter front plate 26 so as to be moved in the optical axis direction of the body, and when the main lens GM is moved in the optical axis direction together with the mirror barrel 16, focusing can be attained. Since it is unnecessary to adopt water-proof structure in case of moving the main lens GM, the constitution can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens for a camera, and more particularly to a photographic lens used in a waterproof camera.

BACKGROUND ART Conventionally, in everyday waterproof cameras, a waterproof glass for waterproofing is installed in front of a photographic lens in a watertight manner with respect to the camera body. Here, flat glass is used as this waterproof glass.

This is because a photographic lens with existing performance and specifications is used as the main lens, and its performance and specifications are not impaired by the waterproof glass. However, this configuration has the disadvantage that the entire length of the photographing optical system including the waterproof glass becomes thick due to the space between the waterproof glass and the main lens.

The present invention has been made in view of these conventional drawbacks, and its purpose is to further shorten the overall length of the photographing optical system including the waterproof glass, and to simplify the configuration for focusing.

In order to achieve this object, the present invention is characterized in that the waterproof glass is a positive lens with a convex surface facing the object side, and that focusing is performed only by the main lens placed on the image side of the waterproof glass. .

Examples of the present invention will be described below. FIG. 1 is a longitudinal sectional view showing a waterproof camera according to an embodiment of the present invention. In the figure, the casing of the camera (2) is attached to the front cover (4).
, a rear cover (6), and a back cover (8), each of which has a watertight structure and is combined with each other to form a watertight exterior part as a whole.

The rear cover (6) has a groove (6a) formed therein, and the front cover (4) has a convex portion (6a) that fits into the groove (6a).
4a) is formed, and this protrusion (4a) fits into the groove (6a) across the QIJ song lO), thereby making the front cover (4) and the extraction force bar (6) watertight. be combined. In addition, the rear cover (6
) is formed with a recess (6b), and the back cover (8) is integrally formed with a backing (8a) that fits into this recess (6b), and this backing (8a) is connected to the recess (6b).
By fitting the back cover (8) and the rear cover (6) together, the back cover (8) and the rear cover (6) are watertightly connected.

(Ga) is waterproof glass consisting of a positive lens with a convex surface facing the object side, and is integrally held in a watertight manner by a waterproof glass holder (12). This waterproof glass holder (12) is attached to the front cover (4) via the O-ring (14).
are fitted and connected watertightly. (GM) is a main lens arranged on the image side of the waterproof glass (C;a) and has positive refractive power, and the main lens (GM) is held by a lens barrel (16). This lens barrel (16) is supported movably in the optical axis direction relative to the main body by a shutter front plate (26), which will be described later.

Focusing is performed by moving this main lens (GM) together with the lens barrel (16) in the optical axis direction.

In this way, the positive refractive power required for the photographic optical system is shared between the waterproof glass (Ga) and the main lens (GM), and the waterproof glass is integrally combined with the front cover (4) for waterproofing. By performing focusing only with the main lens (GM), excluding the (Ga) lens, there is no need to adopt a waterproof structure when moving the main lens (GM), so the configuration can be simplified.

To explain this focusing mechanism in detail, the lens barrel (1
6) is biased toward the object by the spring (18);
Focusing is performed by being driven and locked by a drive mechanism (20) at a position corresponding to the subject distance detected by a distance measuring device (not shown).

(22) is a light shielding plate that prevents harmful light from entering inside the body, and this light shielding plate (22) is connected to the shutter base plate (24).
is fixed. Furthermore, (26) is a shutter front plate, and this shutter front plate (26) and shutter base plate (24)
A shutter chamber is constituted by the shutter chamber, and a shutter blade (28) is housed in this shutter chamber.

Note that if the refractive power of the waterproof glass (Ga) consisting of a positive lens is too weak, the total lens length from the object side of the waterproof glass (Ga) to the image plane cannot be sufficiently shortened, and conversely, the waterproof glass (Ga) If the refractive power of (Ga) is too strong, the refractive power of the main lens (GM) will become weak, the amount of movement during focusing will increase, and the amount of aberration fluctuation during focusing will also increase, which is not preferable. Therefore, it is desirable to satisfy the following conditions.

o, os<ψa/ψ, <o: s Here, ψ3 is the refractive power of the waterproof glass, and ψ2 is the combined refractive power of the waterproof glass and the main lens. The above conditions define the refractive power of the waterproof glass, and if the upper limit is exceeded, the refractive power of the main lens becomes too weak, resulting in an increase in the amount of focusing movement and the amount of aberration variation during focusing. Conversely, if the lower limit of the above conditions is exceeded, it becomes difficult to sufficiently shorten the overall lens length.

Next, it will be optically explained that the total lens length is shortened by the present invention. FIG. 2 schematically shows the photographing optical system, where fa) shows the case where the waterproof glass is a flat glass as in the conventional case, and (bl shows the case of the present invention.
In the figure, fa is the focal length of the waterproof glass, fM is the composite focal length of the entire photographing optical system, Cb is the focal length of the main lens, a is the distance between the waterproof glass and the main lens, and Ll and L are the lenses in each case. Full length. In the case of the conventional example of +al, f
When paraxial tracing is performed for an on-axis ray with a=(1), 1b=-, and an image height of 1, LL=3+fM. On the other hand, in the case of the fblO invention, the paraxial beam is =
a+h, /α鵞'-a+h, ・fM. here,
hM is the incident height of the ray to the main lens, α, / is the exit angle from the main lens, and as is clear from the figure, o (h mushroom (
It is l. Therefore, Ll - Lj = (1-1'12)
fM:> o Therefore, the total lens length of the present invention is clearly shorter.

In addition, in the present invention, by making the waterproof glass a positive meniscus lens convex toward the object side as in the above embodiment, the position of the waterproof glass during paraxial tracing is placed closer to the object side, and the total length of the lens can be reduced. It can be made even shorter.

As described in detail above, the waterproof camera lens according to the present invention includes, in order from the object side, a positive lens convex toward the object side, a waterproof glass watertightly fixed to a camera body consisting of a watertight casing, and a positive refracting lens. It is characterized by having a main lens that has a force and moves in the optical axis direction for focusing, and by configuring it in this way,
The overall length of the lens can be made shorter, and the configuration for focusing can also be simplified.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is a schematic diagram of an optical system. (Ga): Waterproof glass, (GM): Main lens. that's all

Claims (1)

[Claims] 1. In order from the object side, a waterproof glass watertightly fixed to a camera body consisting of a watertight casing consisting of a positive lens convex to the object side, and a lens having a positive refractive power for focusing. A waterproof camera lens characterized by having a main lens that is moved in the optical axis direction. 2. A waterproof camera lens according to claim 1, which further satisfies the following conditions: 0.05<ψ_a/ψ_M<0.8, where ψ_a is the refractive power of the waterproof glass. , ψ_M: composite refractive power of the waterproof glass and the main lens.