Photography – With viewfinder – With prism
Reexamination Certificate
1997-09-26
2001-07-24
Mathews, Alan A. (Department: 2851)
Photography
With viewfinder
With prism
C396S150000, C396S354000, C396S373000, C359S507000
Reexamination Certificate
active
06266490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an antistatic viewfinder, and more particularly, to a viewfinder used in such things as a camera using silver halide film, an electronic image recording device or binoculars.
2. Description of the Prior Art
Conventionally, either glass or resin has been used in optical systems, but the use of resin has increased in recent years due to its superior malleability and lower cost. Normally, resin easily attracts static atmospheric charge, allowing dust and dirt particles to easily adhere to the surface of the resin via adsorption. Consequently, if for example optical members of a viewfinder equipped with an eyepiece are constructed of resin, the problem arises that the dust and dirt particles that have become adhered to area around the image plane of the object image become enlarged and easily visible.
In response to this problem, one countermeasure is to clean the surfaces of the optical members prior to their incorporation into the optical systems and make the viewfinder airtight, thereby preventing dust and dirt particles from adhering to the optical members. Another countermeasure is to lower the surface resistance of the optical member by either applying an antistatic coating or mixing an antistatic agent into the resin, thereby making It more difficult for the surfaces to become charged and for dust and dirt particles to adsorb to them.
However, because adsorption Is operating on the dust and dirt particles adhering to the surfaces of the optical member due to electrostatic charging of the optical member, it is very difficult to eliminate them completely even if the surfaces of the optical members are cleaned. Moreover, the application of an antistatic coating does not affect the dust and dirt particles that are already adhering to the surfaces of the optical member, and increases the cost of manufacture as well. In addition, with the method involving the mixture of an antistatic agent Into the resin, while the antistatic agent continues to seep out toward the optical member surfaces in small amounts and an antistatic property, i.e., an anti-charging property, is maintained, this continues for only about a year. Further, there is another problem that the dust and dirt particles that have adhered to members other than the optical members In the viewfinder block, such as holders or the field mask, move to the surfaces of the optical members.
SUMMARY OF THE INVENTION
The present invention was made in view of this situation. The technical Issue to be resolved by the present invention is to prevent the components of a viewfinder from becoming charged and to provide an antistatic viewfinder in which dust and dirt particles are not present to a noticeable extent.
In order to resolve the technical issue described above, the present invention Is essentially a viewfinder equipped with an eyepiece, in which at least the member regarding which focusing is performed when observation is made through the eyepiece, or the members located near said member, are made of antistatic resin. In the present invention, a dust prevention effect is efficiently obtained by using antistatic resin for members as to which a dust prevention effect is desired. It is acceptable if all components of the viewfinder are made of antistatic resin.
The antistatic resin referred to above is a resin that is itself given ionic conductivity.
In the construction described above, an antistatic resin obtained by giving the resin itself ionic conductivity has a low surface resistance and does not easily become charged. Moreover, the antistatic effect lasts longer in comparison with the method in which an antistatic coating is applied to the surfaces or in which an antistatic agent is mixed into the resin.
Therefore, by using such a resin having a relatively longer-lasting antistatic effect for the optical members near the image plane that is observed through the eyepiece, a viewfinder may be obtained in which dust and dirt particles are not noticeably present over a long period of time.
Preferably the present invention may be realized in various forms as shown below.
A first embodiment is a Keplerian real image viewfinder using which the object image formed by means of the object lens is observed through the eyepiece, wherein optical members located near the image plane on which the object image is formed, i.e., transparent or semi-transparent members through which light passes—lenses and prisms, for example—are made of antistatic resin.
In this construction, by using antistatic resin for optical members near the image plane on which the object image is formed by means of the object lens, it can be made difficult for dust and dirt particles to adhere to these optical members without their undergoing special processing, such as the application of an antistatic coating, and cleaning of dust and dirt particles that do adhere to the optical members can be made easier. In this way, the amount of dust and dirt particles near the image plane of the object image that is observed through the eyepiece may be easily reduced or eliminated.
Therefore, the antistatic viewfinder having the construction described above may prevent the viewfinder components from becoming charged and the dust and dirt particles from becoming noticeably present.
A second embodiment is a Keplerian real image viewfinder using which the object image formed by means of the object lens is observed through the eyepiece, wherein holding members that hold the optical members and field stop, and that are located near the image plane on which the object image is formed, are made of antistatic resin.
In the construction described above, by using antistatic resin for the molding of the holding members near the image plane on which the object image is formed by means of the object lens, the amount of dust and dirt particles that adhere to the holding members may be reduced, and the amount of dust and dirt particles that move from the holding members to the surfaces of the optical members and are viewed through the eyepiece may be easily reduced or eliminated.
Therefore, the antistatic viewfinder having the construction described above may prevent the viewfinder components from becoming charged and the dust and dirt particles from becoming noticeably present.
A third embodiment is a Keplerian real image viewfinder using which the object image formed by means of the object lens is observed through the eyepiece, wherein the field stop located near the image plane on which the object image is formed is made of antistatic resin.
In the construction described above, by using antistatic resin for the field stop located near the image plane on which the object image is formed by means of the object lens, the amount of dust and dirt particles that adhere to the field stop may be reduced, and the amount of dust and dirt particles that move from the field stop to the surfaces of the optical members and are viewed through the eyepiece may be easily reduced or eliminated.
Therefore, in the antistatic viewfinder having the construction described above, electrostatic charging is prevented and dust and dirt particles do not become noticeably present.
The present invention may be applied to viewfinders other than real image viewfinders.
A fourth embodiment is an Albada reverse-Galilean viewfinder in which at least the member on which the optical image frame is placed is made of antistatic resin.
In the construction described above, the member on which is located the optical image frame to perform display of the field of view and the AF area is located near the image plane that is observed through the eyepiece. By having the member on which the optical image frame is placed be made of antistatic resin, it becomes difficult for dust and dirt particles to adhere to surfaces near the image plane observed through the eyepiece.
Therefore, a viewfinder may be obtained in which dust and dirt particles are not noticeably present.
A fifth embodiment is an illuminated reverse-Galilean viewfinder in which at lea
Maeda Yasuo
Mukai Hiromu
Burns Doane , Swecker, Mathis LLP
Mathews Alan A.
Minolta Co. , Ltd.
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