JPH02113203A - Luminous flux decomposing prism - Google Patents

Abstract

PURPOSE:To reduce the cost and weight of the prism by injecting a melt radially to a prism mounting plate in the thickness direction from nearly the central part of the plate. CONSTITUTION:An injecting gate 2 is disposed nearly at the center of the mounting plate 1 in such a position where a molten liquid crystal polymer spreads radially and uniformly around the gate 2 and is thereby so devised as to sufficiently utilize the properties of the liquid crystal polymer. Namely, the liquid crystal polymer has a small coefft. of linear expansion in a fluid direction and, therefore, the difference between the coeffts. of linear thermal expansion of a prism mounting base and the prism is in a permissible range. The sufficient coefft. of linear thermal expansion is, therefore, provided over the entire part of the mounting base by injecting the polymer to the mounting base nearly from the central part. The optical performance is maintained in this way while the prism is relatively inexpensive and light in weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light beam splitting prism for guiding a photographing light beam to an imaging member such as a multi-tube camera or a multi-plate camera.

[Prior art] Conventionally, in multi-tube or multi-plate cameras,
In order to guide the light flux to the plurality of imaging members, a light flux splitting prism composed of a plurality of prism blocks is used.

The prism mounting plate holds each prism block integrally and attaches the light beam splitting prism to the camera body.

By the way, it is necessary to provide this prism with sufficient optical performance, and to do so, it is necessary to select materials for the prism block and prism mounting plate that can withstand changes in the external environment. For example, in order to prevent image shift due to temperature changes, it is necessary to make the thermal expansion coefficients of the prism block and the prism mounting plate approximately equal. The prism mounting plate must also have mechanical strength.

Therefore, conventionally, a ceramic sintered body is generally used as a material having substantially the same linear thermal expansion coefficient as the prism block.

[Problems to be Solved by the Present Invention] However, ceramic sintered bodies are heavy and expensive. Therefore, this ceramic sintered body is generally used in relatively large and expensive professional cameras, and is not often used in consumer video cameras or still video cameras. The mainstream of consumer cameras is single-chip video cameras that do not use prisms.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a prism that is relatively inexpensive and lightweight, and can maintain optical performance.

[Means for solving the problem] In recent years, liquid crystal polymers that exhibit liquid crystallinity in the molten state have been produced, but they can be injection molded and have a specific gravity that is about 1/3 that of ceramics. be. The coefficient of linear expansion becomes smaller in the flow direction during injection molding, and is 1/4 compared to other engineering plastics such as polycarbonate.
~1/10 or less.

The present invention proposes a prism mounting plate that uses liquid crystal polymer and has a linear expansion coefficient adjusted in a desired direction.

[Example] The present invention will be explained in detail below.

First, liquid crystal polymers exhibit crystalline properties even though they are in a liquid state, and even if they are cooled as is, they solidify with their molecules oriented, and this state remains stable. In particular, the coefficient of linear thermal expansion in the flow direction is very small, and in the direction perpendicular to the flow direction, it exhibits anisotropy of about 2-y6 times and a value on the order of lXl0-'.

This is an order of magnitude lower than normal plastics and comparable to metals.

FIG. 1 shows a perspective view of a prism mounting plate according to the present invention.

1 is a thin film-like prism mounting plate made of liquid crystal polymer, 2
indicates the position of the injection gate through which molten liquid crystal polymer is injected during injection molding. Note that the arrow indicates the flow direction of the liquid crystal polymer injected from position 2 corresponding to the injection gate of the injection mold (not shown). This injection gate is placed approximately at the center of the mounting plate in a position where the molten liquid crystal polymer spreads uniformly radially around the injection gate, making full use of the properties of the liquid crystal polymer. .

In other words, since the liquid crystal polymer as described above has a smaller linear thermal expansion coefficient in the flow direction, the difference in linear thermal expansion coefficient between the prism mount and the prism is within an allowable range in a given direction.

Therefore, by injecting from approximately the center, the entire mount can have a sufficient coefficient of linear thermal expansion.

The mounting plate 1 has an elongated hole 1b along the optical axis of the photographic lens for position adjustment when attaching to the camera body, a positioning hole 1a for determining the position, and a hole 1a for determining the position. Holes lc and ld are provided.

FIG. 2 shows an overall perspective view of the beam splitting prism. 3a,
3b and 3c are color separation prisms for dividing the light flux from the photographing lens 4 into R, G, and B, respectively. O is the optical axis, 5
is a CCD. Note that the fitting and the prism are joined via an adhesive.

As explained above, by injecting the molten material radially from the approximate center of the prism mounting plate from the thickness direction, it is possible to manufacture a prism mounting plate with a small linear expansion coefficient on the adhesive surface with the color separation prism. , it is possible to significantly reduce costs and weight compared to conventional ones.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a mounting plate related to the present invention, and FIG. 2 is a perspective view of a color separation prism. 1... Mounting is on plate 3... Color separation prism

Claims (1)

[Claims] In a light splitting prism comprising a plurality of prism blocks for splitting a light beam from a photographic lens and a prism mounting plate for integrally holding the prism blocks,
A light flux splitting prism characterized in that, when the prism mounting plate is injection molded with a liquid crystal polymer, an injection gate for the liquid crystal polymer is disposed approximately in the center of the prism mounting plate.