Patent Description:
In the <CIT>, a lens barrel is proposed to enable to change a diaphragm to cut off harmful rays in accordance with the size of the image circle. However, a prior lens barrel cannot reduce effects of catoptric light due to bayonet mounts. Additional relevant prior art are <CIT>, <CIT>, <CIT>, <CIT>,<CIT> and <CIT>.

An object of the present invention is to provide a lens barrel and a camera system enabling to reduce effects of catoptric light.

The present invention can provide a lens barrel enabling to reduce effects of catoptric light and a camera system including said lens barrel. In the present invention, an object to reduce effects o catoptric light is achieved by changing the arranged position or the size of bayonet mount projections.

Below, the present invention will be explained in detail based on the embodiments illustrated in the figures, wherein.

As shown in <FIG> and <FIG>, a lens barrel-type imaging equipment represented by single-lens reflex camera typically includes a lens barrel <NUM> and a camera body <NUM>. A lens barrel-side fitting part <NUM> held on the back of the lens barrel <NUM> is detachably attached to a body-side fitting part <NUM> held on the front of the camera body <NUM>.

To the inside of a barrel body of a lens barrel <NUM> shown in <FIG>, multiple optical lens groups (not shown in the figure) are attached movably in the direction of an optical axis. As shown in <FIG>, a camera body <NUM> holds a low-pass filter <NUM> and an imaging device <NUM>. The imaging device <NUM> includes magnifying-type solid-state image sensing devices such as CMOS other than CCD.

A reason to provide a low-pass filter <NUM> is following. In the imaging device <NUM> of the camera body <NUM>, a phenomenon called a false color or a color moire can occur resulting in a different coloring from an actual one when a light with high spatial frequency enters in a single pixel of the imaging device <NUM>. This phenomenon can be reduced by setting the low-pass filter <NUM> at an object side of the imaging device <NUM>.

As shown in <FIG>, to the inside of the camera body <NUM>, a mirror box <NUM> is attached at a predetermined position relative to body frames 30a and 30b of the body <NUM>. The imaging device <NUM> and the low-pass filter <NUM> are attached to the body frame 30b at a predetermined position. Note that a body frame 30c is attached to the back of the imaging device <NUM>.

A mirror not shown in figures is placed in the mirror box <NUM>, which leads an object light entering parallel to an optical axis in the direction of a finder when not taking pictures; and which leads an object light in the direction of the imaging device <NUM> by moving the mirror when taking pictures.

As shown in <FIG>, the imaging device <NUM> is rectangular in shape when viewing vertically from an optical axis L1, which is smaller than a rectangular cross-section of an inner opening site 40a of the mirror box <NUM>. A cross section of an inner opening site of a body frame 30b shown in <FIG> is rectangular as well as that of the inner opening site 40a of the mirror box <NUM>. On the other hand, a cross-section of an inner opening site of a body frame 30a positioned at the object side in the direction of the optical axis L1 of the mirror box <NUM> is circular. To the front of the body frame 30a, a ring-shaped body-side fitting part <NUM> is attached.

As shown in <FIG> and <FIG>, the barrel-side fitting part <NUM> held on the back of the lens barrel <NUM> is ring-shaped in the whole to accommodate the shape of the lens barrel <NUM>. on the barrel-side fitting part <NUM>, a barrel-side fitting plane <NUM> is formed substantially vertical to an optical axis L1 of an optical lens group. The barrel-side fitting plane <NUM> can be attached tightly to a body-side fitting plane <NUM> formed on a body-side fitting part <NUM> of a camera body <NUM>. The body-side fitting plane <NUM> is also substantially vertical to the optical axis L1 of the optical lens group.

Both of the barrel-side fitting part <NUM> and the body-side fitting part <NUM> are made of metal, and can be detachably attached in the so-called style of a bayonet mount. That is, as shown in <FIG>, three barrel-side mount projections <NUM> are formed at unequal intervals in the circumferential direction on the imaging surface side in the direction of the optical axis in the barrel-side fitting part <NUM>.

As shown in <FIG>, barrel-side mount projections <NUM> are extended out radially from a cylindrical inner circumference face <NUM> of the barrel-side fitting part <NUM>. Three barrel-side mount projections <NUM> arranged along the circumference as shown in <FIG> are connected in the circumferential direction by a cylindrical stiffened member <NUM>. The radial thickness of the cylindrical stiffened member <NUM> is approximately a half or smaller of the radial width of the mount projections <NUM>.

As shown in <FIG> and <FIG>, body-side mount projections <NUM> are formed on the inner circumference face of the body-side fitting part <NUM> at the position corresponding to the barrel-side mount projections <NUM> at unequal intervals in the circumferential direction. The inner diameter of the body-side mount projection <NUM> is equal to or slightly larger than the outer diameter of the cylindrical stiffened member <NUM>. The outer diameter of the barrel-side mount projection <NUM> is slightly smaller than the inner diameter of the body-side fitting part <NUM> without body-side mount projections <NUM>.

The lens barrel <NUM> in <FIG> is fitted to the camera body <NUM> in <FIG> as follows: the mount projections <NUM> in the barrel-side fitting part <NUM> shown in <FIG> are pressed into the inside of the body-side fitting part <NUM> at the position in the circumferential direction where body-side mount projections <NUM> shown in <FIG> are not formed.

After that, the lens barrel <NUM> is rotated around the optical axis L1 to put the mount projections <NUM> of the barrel-side fitting part <NUM> in the imaging surface side of the body-side mount projections <NUM> of the body-side fitting part <NUM> where the lens barrel <NUM> is fitted to the camera body <NUM> in the bayonet-type.

As shown in <FIG> and <FIG>, a circular-shaped electric contact holding member <NUM> is fixed on the imaging surface sides in the direction of the optical axis of the cylindrical stiffened member <NUM> of the barrel-side fitting part <NUM> and the mount projections <NUM>. The electric contact holding member <NUM> is comprised of an insulating member such as plastic, and two or more barrel-side electric contact points <NUM> may be placed on the outer circumferential face of the holding member <NUM> for example. These barrel-side electric contact points <NUM> are detachably connected by rotation to each body-side electric contact point <NUM> placed on the inner circumferential face of a body frame 30a.

In the present embodiment, the electric contact holding member <NUM> is fixed at the barrel-side fitting part <NUM> as shown in <FIG> so that the most of the holding member <NUM> is above the upper long side of an inner opening site 40a with a rectangular cross-section in the mirror box <NUM>. When fixing the electric contact holding member <NUM> at the barrel-side fitting part <NUM>, at least barrel-side electric contact points <NUM> has to be placed above the upper long side of the inner opening site 40a with a rectangular cross-section.

Further, as shown in <FIG>, three barrel-side mount projections <NUM> are placed at unequal intervals in the circumferential direction so as to satisfy the following relationship: one of three barrel-side mount projections <NUM> is above (outside) the upper long side of the inner opening site 40a with a rectangular cross-section, another mount projection <NUM> is outside the right short side of the inner opening site 40a, and the last mount projection <NUM> is below (outside) the lower long side of the inner opening site <NUM> a. It means that the mount projections <NUM> placed on the lens barrel <NUM> are not exposed at four corners 11a, 11b, 11c and 11d of the opening site 40a where only the cylindrical stiffened nember <NUM> is exposed.

Note that the arranging position in the circumferential direction of the body-side mount projection <NUM>, which forms a bayonet structure in pairs with the barrel-side mount projection <NUM>, is same as that of the barrel-side mount projection <NUM>.

As shown in <FIG> and <FIG>, in a lens barrel <NUM> according to a comparative example of the invention, three barrel-side mount projections <NUM> are placed at equal intervals on the barrel-side fitting part <NUM> regardless of the shape of the cross-section of the inner opening site 40a in the mirror box <NUM>. Therefore, as shown in <FIG>, a part of the mount projection <NUM> placed on the lens barrel <NUM> is exposed at four corners 21a, 21b, 21c and 21d of the opening site 40a when viewing the direction of the lens barrel <NUM> from a low-pass filter <NUM>. The mount projections <NUM> are exposed at two of the four corners, 21a and 21b, and the exposed area is large.

The light <NUM> passing through the inside of the lens barrel <NUM> can pass through the low-pass filter <NUM> to enter an imaging device <NUM>, or can be reflected on the face of the low-pass filter <NUM> instead of passing through it.

Usually, this catoptric light hits the inner surface of the camera body <NUM> or the lens barrel <NUM>, diffuse to fade, or be absorbed, but in rare cases, it can enter the imaging device <NUM> after reflecting again on the end face of the bayonet-type mount projection <NUM> placed on the lens barrel <NUM>. This second catoptric light can hit at the inner surface of the camera body <NUM> if reflecting regularly on the end face of the bayonet-type mount projection <NUM>, but actually, it rarely reflects regularly since there is microasperity on the end face of the mount projection <NUM> due to machine process.

When the second catoptric light 52b and 52c enter the imaging device <NUM>, it is possible to become a ghost or a flare to deteriorate picture quality. Note that the light ray <NUM> can reflect on the imaging device <NUM>, and also in the case of a silver salt film camera, on the surface of the film. In the end face in the optical axis direction of the barrel-side fitting part <NUM>, the projection <NUM> has a broader width in the radial direction, where more catoptric light may hit to easily increase ghosts and flare.

Therefore, in the present embodiment, the above-described configurations of the bayonet-type mount projections <NUM> and <NUM> solve the above problems. Hereinbelow, the arranged position of the mount projections <NUM> will be explained. An explanation on the mount projections <NUM> will be skipped since they have the same arranged position as the mount projections <NUM>.

As shown in <FIG>, the mount projections <NUM> are arranged to avoid the vicinity of four corners 11a, 11b, 11c and 11d of a light flux L with a rectangular cross-section that goes from the lens barrel <NUM> to enter the imaging device <NUM>. Actually as shown in <FIG>, the mount projections <NUM> are arranged not to overlap four corners of the opening site 40a. Therefore, the mount projections <NUM> are not on the diagonal line of the low-pass filter <NUM>, and not exposed on the inside of the opening site 40a.

When viewing the lens barrel <NUM> from the low-pass filter <NUM>, four portions of the barrel-side fitting part <NUM> placed on the lens barrel <NUM><NUM> are exposed at four corners 11a, 11b, 11c, and 11d of the opening site 40a as shown in <FIG>. However, the exposed area is small and the effect of the catoptric light is low since the exposed portions are not the mount projections <NUM>.

As the mount projections <NUM> are not exposed on the inside of the opening site 40a, the catoptric light <NUM> from the low-pass filter <NUM> does not enter the mount projection <NUM> as shown in <FIG>. Therefore, the effect of catoptric light to reflect on the mount projection <NUM> can be reduced to prevent flares and ghosts and to minimize degradation.

Further, when the lens barrel <NUM> is a bright optical lens barrel with F value of <NUM> or less, a telephoto lens barrel, or a large diameter lens barrel for instance, light passes right next to the barrel-side fitting part <NUM> causing that the catoptric light easily affects, and therefore, it is meaningful to prevent the catoptric light from entering the mount projection <NUM>. Also, the effects of the present embodiment are more significant when the distance between the imaging device and the mount projections are closer, e.g. when the imaging device is large (e.g. <NUM> x <NUM> or larger), or when the diameters of the barrel-side fitting part <NUM> and the body-side fitting part <NUM> are small.

Also, a coating material is applied on components such as a lens holding rim inside the lens barrel <NUM> (See <FIG> and <FIG>). However, the coating may peel off to adhere to the lens or the low-pass filter <NUM> if applying it on the exterior of the barrel-side fitting part <NUM> that is rubbed when fitting the lens barrel <NUM> and the camera body <NUM>. It is also unfavorable to apply a coating only on the mount projection <NUM> to prevent reflection, which is a protruding portion and may be easily rubbed and pealed off while removing the lens barrel <NUM> from the camera body. However, in this embodiment, it is possible to obtain good characteristics as the configuration of the mount projections <NUM> and <NUM> prevents reflection instead of applying any coating.

As shown in <FIG>, in a lens barrel <NUM>-<NUM> according to the second embodiment in the invention, the bayonet-type mount projection <NUM> has the same arranged position as the mount projection <NUM> according to the comparative example shown in <FIG>. However, a notch <NUM> is formed on the mount projection 12a so as to avoid the inner opening site 40a of the mirror box <NUM> in the lens barrel <NUM>-<NUM> in the present embodiment.

The second embodiment has advantages that it is easy to design and unnecessary to change in basic configuration of a bayonet-type mount projection <NUM> of the camera body <NUM> since the mount projections <NUM> can be arranged at equal intervals in the circumferential direction. Other configuration and effects in the present embodiment is same as in the above-described first embodiment.

As shown in <FIG>, in a lens barrel <NUM>-<NUM> according to the third embodiment, each of two mount projections 12b are arranged on outside of the long sides in a cross-section of the inner opening site 40a of the mirror box <NUM>. This configuration results in no exposure of the mount projection 12b on the inside of the opening site 40a. other configuration and effects in the present embodiment is same as in the above-described first embodiment.

As shown in <FIG>, in a lens barrel <NUM>-<NUM> according to the forth embodiment, the diameters of the inner circumferences of the barrel-side mount projection 12c and the cylindrical stiffened member <NUM> are designed equal to or longer than the length of the diagonal line of the inner opening site 40a of the mirror box <NUM>. Also, both of a barrel-side mount projection 12c and a cylindrical stiffened member <NUM> are designed not to be exposed on the inside of the inner opening site 40a. Other configuration and effects in the present embodiment is same as in the above-described first embodiment.

As shown in <FIG>, in a lens barrel <NUM>-<NUM> according to the fifth embodiment, a barrel-side mount projection <NUM> is arranged similar to that in the first embodiment. Each of two electric contact holding members 70a and 70b is arranged on the outside of the long sides of the cross-section of the inner opening site 40a in the mirror box <NUM>. The outer circumferences of electric contact holding members 70a and 70b have barrel-side electric contact groups 72a and 72b respectively.

In the present embodiment, the number of the contact points at each of the electric contact groups 72a and 72b placed on the each of the electric contact holding members 70a and 70b can be reduced since the electric contact groups 72a and 72b are divided into two to exchange signals between the-lens-barrel <NUM>-<NUM> and the camera body. As a result, the length in the circumferential direction can be reduced in each electric contact group 72a and 72b, and they can be arranged in a smaller space. Further, it results in increasing the flexibility in design regarding the space between the electric contact groups 72a and 72b and becoming easier to arrange each of the electric contact holding members 70a and 70b to avoid the inner opening site 40a of the mirror box <NUM>.

Further, the arrangement to separate the electric contact groups 72a and 72b each other reduces interference between contacts, resulting in improving S/N ratio. For example, an electromagnetic ray may easily occur at a contact point for electric power supply where relatively large electric current passes. It can reduce an electric signal noise at a contact point for signal to separate a contact point for electric power supply from that for signal. Other configuration and effects in the present embodiment is same as in the above-described first embodiment. Note that the electric contact holding member where electric contact groups are placed is divided into four so that each can be arranged at the outside of four lines of the inner opening part 40a of the mirror box <NUM> respectively.

The following conversion is possible in each embodiment.

Claim 1:
A lens barrel comprising a barrel (<NUM>) holding an optical system, characterized by further comprising
four mount projections (<NUM>) engageable with a photographic device having an imaging unit where light flux impinges from the optical system,
barrel-side electric contact points (<NUM>) electrically connectable with body-side electric contact points provided to the photographic device,
an electric contact holding member (<NUM>) where the barrel-side electric contact points (<NUM>) are fixed, and
a barrel-side fitting part (<NUM>) fixed on a side of the barrel that is engaged with the photographic device, wherein
the photographic device comprises an inner opening site (40a) defining the light flux impinging from the optical system to the imaging unit, the inner opening site (40a) being rectangular in shape when viewing from an optical axis direction,
the four mount projections (<NUM>) are arranged so as to position on the left, right, top and bottom of outside the inner opening site (40a) of the photographic device when the barrel (<NUM>) is fitted to photographic device,
the electric contact holding member (<NUM>) is fixed at the barrel-side fitting part (<NUM>) so that, when the barrel (<NUM>) is fitted to photographic device, the most of the electric contact holding member (<NUM>) is above an upper long side of the inner opening site (40a) of the photographic device, and
the barrel-side electric contact points (<NUM>) are arranged outside the upper long side of the inner opening site (40a).