JPH0235428A - Mount adapter - Google Patents

Abstract

PURPOSE:To combinate and use an interchangeable lens in which a difference between a flange back and a mount in a diameter is small and another type of a camera by incorporating specified auxiliary optical systems in a mount adapter. CONSTITUTION:The auxiliary optical systems 2 and 3 are provided on an adapter ring 1 where a lens mounting female screw 1a is formed on a front edge and a camera mounting male screw 1b on a rear edge. Then a pint difference due to thickness in an optical axis direction generated by mounting the mount adapter is corrected by the optical systems 2 and 3. For example, light directed toward the focus F11 of a lens 11 is finally allowed to converge on the focus F12 of an auxiliary lens 13 by arranging the auxiliary lenses 12 and 13 in the back of the lens 11, and focal distance is extended by the pint difference.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mount adapter used for connecting different types of interchangeable lenses and a camera body.

[Prior art]

Conventionally, when using a removable interchangeable lens with a camera body of another model, if the flange back of the interchangeable lens is larger than the flange back of the camera body, an adapter ring as shown in Fig. 3 with a thickness equal to the difference in thickness is used. It could be installed if used. However, if the difference in flange back between the two is small or nonexistent, or if the flange back of the camera body is larger than the flange back of the interchangeable lens, installation is only possible if the interchangeable lens is smaller than the camera body due to the diameter of the part. , it was possible to connect different models of interchangeable lenses to the camera body using an adapter.

FIG. 4 shows an adapter of this kind.

[The problem that the invention is trying to solve] However,
When attaching a flange back, if both diameters were almost the same, it would be impossible to attach, or it would be possible to take pictures only at short distances with the adapter ring extended by the thickness of the adapter ring.

Comparing lenses for 2/3-inch image sensors and lenses for 1/2-inch image sensors in recent video cameras, we find that optical elements (e.g. crystal plate, phase plate, near-infrared cut filter, The difference in the total thickness of the lenses (cover glass, etc.) is small, and therefore the difference in back focus is also small. Also, the difference in the effective diameter of the rear lens is small, so if it is an interchangeable lens type, the flange back and mount diameter will be almost the same. In this case, although it is optically possible to use a 2/3-inch lens in combination with a 1/2-inch image sensor, it is not possible due to mechanical size constraints.

[Means for solving problems]

The present invention can be applied to interchangeable lenses and camera bodies of different types with substantially the same flange back and mount diameter.
It is characterized by being able to be connected by using a mount adapter equipped with an auxiliary optical system.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which an auxiliary optical system 2.3 is held in an adapter ring l having a female thread la for lens attachment at the front end and a male thread lb for camera attachment at the rear end. .

Figure 2 shows an example of the auxiliary optical system. An auxiliary lens 12 having a focal length f2 is placed behind the lens 11 having a focal length f1 with a principal point spacing e1, and an auxiliary lens 13 having a focal length f3 is further placed with a principal point spacing e2 apart. The axial light beam incident from infinity is focused on the focal point F, 1' of the lens 11. Now if we choose f2 so that f, +f2=el,
The light directed toward F and 1' becomes parallel to the optical axis, and the lens 11 and the auxiliary lens 12 form an afocal system. Therefore, focus F1. The light heading towards ' is finally focused on the focal point F' of the auxiliary lens 13 . The composite focal length f is f! Since f=-1・f3, if f3 is chosen so that F2=-f3, then f
= f.

In other words, the focal length does not change, and the final image point F from the lens 11
' can be extended by the principal point spacing e2.

In this case, the principal point spacing e2 can be arbitrarily selected, but if it is too large, the amount of peripheral light will decrease.

When an interchangeable lens with a large effective image circle is used in a camera body with a small effective screen size, e2 can be set large because there is margin for peripheral light amount.

It is clear that if the effective diameter of the auxiliary lens is determined so that there is no vignetting of the axial light beam, the F number will not change.

[Other Examples]

In the above embodiment, the axial light flux exiting the auxiliary lens 12 was set to be parallel to the optical axis, but this was done to facilitate understanding, and the imaging magnification by the auxiliary lens 12.13 was approximately 1.0. The focal length and principal point spacing of the auxiliary lenses 12 and 13 may be determined so that

for example f, -e, = -2f2 2f2-e2=-2f3 β2=-1, β3 f=f,・(-1)・(1)=f+ Back focus bf=2f3 given that l.

〔Effect of the invention〕

As explained above, according to the present invention, by incorporating an auxiliary optical system into the mount adapter, it is possible to use an interchangeable lens with a small difference in flange back or mount diameter in combination with a camera body of another model. This makes it possible to use the lens without changing the focal length F-number.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the invention. FIG. 2 is an optical explanatory diagram of an embodiment of the present invention. FIG. 3 is a longitudinal sectional view showing an example of a conventional mount. FIG. 4 is a longitudinal sectional view showing another example of a conventional mount. l...Mount adapter

Claims (2)

[Claims] (1) A mount adapter that is installed between the interchangeable lens and the camera body in order to connect the camera body to a different type of interchangeable lens that has substantially the same distance from the mounting reference plane to the image plane and the same mount diameter. The mount adapter according to the present invention, further comprising an auxiliary optical system for correcting a focus difference caused by a thickness in the optical axis direction caused by attaching the mount adapter. (2) The mount adapter according to claim 1, wherein the auxiliary optical system has an imaging magnification of substantially 1, and the distance between the object point and the image point is a positive value.