JPS61223830A - Zoom lens - Google Patents

Abstract

PURPOSE:To take always photographs under prescribed brightness, by changing the zooming range of a zoom lens in accordance with the condition of aperture values. CONSTITUTION:A diaphragm position signal of a diaphragm position detecting circuit 1 is digitized through an AD converter 2 and a signal voltage for stopping zooming operation correspondingly to a zoom stopping position fN is supplied from a zoom stopping position setting circuit 3 to a zoom end stopping circuit 5 in accordance with the digitized signal. The zoom end stopping circuit 5 compares a zoom position detecting signal from a zoom position detecting circuit 8 with the signal from the zoom stopping position setting circuit 3 and detects whether it is still in a movable area in the zooming range or stopping area. When the zoom operation enters the stopping position, the circuit 5 forcefully makes a zoom control signal to be given to a servo amplifier 6to zero and stops the zooming operation being carried by means of a zoom motor 7.

Description

Detailed Description of the Invention (Industrial Application Field) Misfire QII relates to zoom lenses, and in particular zoom lenses whose open F-number changes when zooming from the wide-angle end to telephoto 4. The present invention relates to a zoom lens which is suitable for use in broadcasting television cameras, video cameras, etc., and allows photographing to be carried out over the entire zoom range at a predetermined aperture value by arbitrarily changing the aperture value.

(Prior Art) Zoom lenses for broadcasting television cameras, video cameras, and the like have been required to be relatively bright, have a high zoom ratio, and be compact as a whole. For this reason, in many zoom lenses, in order to reduce the size of the entire lens, the open F value is not constant over the entire zoom range from the wide-angle end to the telephoto end, but is set so that it gradually becomes darker from near the telephoto end.

For example, in a TV camera zoom lens with a focal length W71f-20 to 500 times the zoom ratio, the focal length is f20.
Open FIII in the zoom range of 0 to 300
1.8, and in the zoom range of focal length/-300 to 500, the aperture F-number gradually decreases from iF/L8, and at the telephoto end focal length f-500, the aperture F-number is about F/3.

As a result, the diameter of the front lens element is reduced and the overall size of the lens (Fig. 9) is reduced.

Therefore, when using such a zoom lens to take pictures with the aperture wide open or close to wide open, such as when there are relatively few clouds in the sky or in the evening, the focal length should be 7, 20 to 30.
In the zoom range of 0, the aperture value is F/L8 or F/L.
Even if a sufficient video signal is obtained near 1.8, the aperture F value becomes dark due to zooming, and the focal length at the telephoto end is f -5.
At 00, the brightness is (1,873)2- compared to the aperture open value in the zoom range of f -20 to 300.
It drops to about 0.36. As a result, it may be difficult to obtain a sufficient video signal, resulting in an image with low contrast. For this reason, the photographer has to perform zooming operations while constantly monitoring the brightness of the subject, that is, the aperture value of the zoom lens, which is very inconvenient in terms of operation.

(Objective of the present invention) The present invention is a zoom lens in which the aperture F value is not constant throughout the zoom range, and the zoom range is arbitrarily changed according to the aperture value to always take pictures at a predetermined brightness. The objective is to provide a 7t zoom lens that can be

(Main feature of the present invention) In a zoom lens having a driving means for electrically driving zooming with different aperture F values at the wide-angle end and the telephoto end, an aperture for detecting the aperture value of the zoom lens. It has a position detection circuit and a zoom range changing means for changing the zoom range using an output signal from the aperture position detection circuit.

Other features of the invention are described in the examples.

(Example 5A) FIG. 2 is an explanatory diagram in which the vertical axis represents the F value, which is the aperture value, of the zoom lens according to the present invention, and the horizontal axis represents the focal length.

The zoom lens shown in the figure is straight! As shown in 21, the open F value is r/i, 7 in the zoom range up to the focal length f (wide-angle lens W), and gradually decreases from the focal length l11fT to the telephoto end T, and at the telephoto end T /28.

FIG. 1 is a block diagram of an embodiment in which the zoom range is changed in the zoom lens of the present invention. In the figure, 1 is an aperture position detection circuit that detects the aperture position of the aperture blades in the zoom lens system, 2 is an A/D converter that converts the aperture position from analog to digital from the aperture position tIL detection circuit 1, and 3 is an A/D converter that converts the aperture position from analog to digital. A zoom stop position setting circuit that generates a signal voltage for changing and limiting the zoom range of the horizontal zoom lens based on the aperture position signal from the A/D converter 2, 4 a controller for performing zooming operations, and 5 a zoom stop position setting circuit. The signal voltage received to change the zoom range from 3 is limited.The zooming operation is stopped immediately before the mechanical end corresponding to the telephoto zoom position.
This is the LI zoom end stop circuit. The zoom end stop circuit 5 shifts the zooming stop position based on the signal voltage value from the zoom stop position setting circuit 3 to variously change the zoom range.

6 is a servo amplifier for zooming; 7 is a driving means such as a zoom motor that drives a zoom ring to perform zooming; 8 is a zoom position detection circuit having, for example, a potentiometer, for detecting the zoom position within the zoom range; 9 is a zoom stop position. a switch for canceling aperture linkage provided as necessary between the setting circuit and the zoom end stop circuit 5;
0 is a comparator for detecting the zoom position where the aperture value changes during zooming and the zoom lens becomes dark.

In this embodiment, the zoom stop position setting circuit 3 and the zoom end stop circuit 5 constitute a part of the zoom range changing means.

Next, the operation shown in FIG. 1 will be explained. First, the zooming operation is performed using the zoom controller 4. The zoom end stop circuit 5 then compares the zoom position detection signal from the zoom position detection circuit 8 with the signal from the zoom stop position setting circuit 3 to detect whether the zoom range is within the movable region or the stop region. And if it is a mechanical end, servo amplifier 6
The zoom control signal given to the zoom motor 7 is forcibly set to zero to stop zooming by the zoom motor 7.

In this embodiment, the zoom motor is protected by driving the zoom motor while decelerating it in response to a command signal from before the scheduled zoom position so as to stop at the nine zoom positions.

Assuming that the aperture position of the zoom lens is F/40 as shown in Figure G2, the focal length from the wide-angle end is fB fN
There is no decrease in light intensity within the zoom range up to Therefore, the F/2.0 aperture position signal from the aD position detection circuit 2 is digitized through the A/D converter 2, and this signal is used to send a signal voltage for stopping corresponding to the zoom stop position fN to the zoom stop position setting circuit 3. Add to the zoom end detection circuit. And focal length l on the telephoto side of the zoom range! !
It is set to shift to the zoom position l1fN. If a slight decrease in light intensity is acceptable, a signal to that effect is input to the zoom stop position setting circuit 3, or the signal voltage from the zoom stop position setting circuit 3 is corrected by a correction circuit (not shown), so that, for example, the F value is adjusted. Pressure may be applied to change the zoom range to a focal length fM corresponding to around F'/zo. In this way, in this embodiment, the zoom range is limited on the telephoto side of the zoom range by zooming from the wide-angle side to the telephoto side, and the aperture is read at the zoom position where the open F value of the zoom lens changes. It is determined based on the aperture value information.

Also, comparator 10 is auto iris 1m aperture control)
M when using fathom! In order to prevent the zoom position at which the zoom position should be stopped from interlocking on the telephoto side and to stabilize the zoom position at which the zoom position should be stopped, the focal point is the point at which the aperture of the zoom lens starts to drop. When the lens passes near the distance 1IlfT, a signal for sampling and holding the aperture position signal is generated and input to the zoom stop position setting circuit 3.

In this embodiment, as shown in Fig. 2, if the aperture during shooting is set to F'/1.7 at full open and 6x9, the usable range of the zoom range is F/9 from the wide-angle end to the focal length #fT. 1.7
It is possible to change the zoom range to have . Also, when the aperture during shooting is F/λ0, the focal length is I from the wide-angle end.
The zoom range with F/10 up to N is changing. In addition, in this example, if a decrease in light amount due to aperture value fluctuation is acceptable depending on the shooting conditions, for example,
If such a signal voltage is input in advance to the zoom stop position setting circuit 3 or the zoom end stop circuit 5, and if the aperture value during shooting is set to F/L7 which is open, the usable range of the zoom range will be changed from the wide-angle end to F. The focal length is set to up to /10.

In this embodiment, the switch 9 may be provided anywhere, for example, on the zoom controller 4, as long as the aperture linkage can be canceled when the subject is bright and this embodiment is not applied.

Further, if the amount of change due to zooming and the decrease in the F value are in an approximately proportional relationship, the aperture position signal may be subjected to analog calculation to rotate the zoom stop position setting voltage.

(Effects of the present invention) According to the present invention, the aperture value can be set arbitrarily depending on the aperture value even when using a zoom lens that is particularly compact and has a variable aperture f-number for television cameras, which is dark at the telephoto end. By changing the zoom range, it is possible to achieve a zoom lens that always maintains a predetermined brightness, minimizes the drop in image level during zooming, and always provides good images.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, and Fig. 2 is an aperture of a zoom lens according to the present invention! Value,! FIG. 3 is an explanatory diagram showing the relationship between one point distance. In the figure, 1 is the aperture position detection circuit, 2 is A
/D:=I inverter, 3 is zoom stop position setting circuit,
4 is a zoom controller, 5 is a zoom end stop circuit, 6 is a zoom amplifier, 7 is a zoom motor, 8 is a zoom position TL detection 1f1 circuit, 9 is a switch, and 10 is a comparator.

Claims (3)

[Claims] (1) In a zoom lens having a driving means for electrically driving zooming, the aperture value differs between the wide-angle end and the telephoto end, and an aperture position detection circuit for detecting the aperture value of the zoom lens and 1. A zoom lens comprising: zoom range changing means for changing the zoom range using an output signal from an aperture position detection circuit. (2) The zoom lens according to claim 1, wherein the change in the zoom range by the zoom range changing means can be canceled by a switch. (3) Limiting the zoom range on the telephoto side of the zoom range is determined by reading the aperture value at the zoom position where the aperture F value of the zoom lens changes when zooming from the wide-angle side to the telephoto side, and using this aperture value information. A zoom lens according to claim 1, characterized in that: