JPH02909A - Lens back variation correction device for camera - Google Patents

Abstract

PURPOSE:To compensate an accurate lens stop point corresponding to the variation of temperature even if said variation occurs in or over the range of ordinary temperature by adding the lens stop point which is not used at ordinary temperature besides the infinity position or the closest photographing position of a lens. CONSTITUTION:A distance detector 2 outputs a distance to an object to a lens feeding control circuit 3 by dividing it, for example, into 1-14 zones. The lens feeding control circuit 3 shifts the zone signal of the distance detector 2 with outputs from a temperature detection circuit 1, so that the zone signals are respectively shifted by -2 in the case of <=-30 deg.C, by -1 in the case of -30 deg.C to -10 deg.C, by 0 in the case of -10 deg.C to 10 deg.C, by 1 in the case of 10 deg.C to 30 deg.C and by +2 in the case of >=30 deg.C to control a lens feeding device 4 according to the zone fitted for the respective signals. The amount matched to the component of the variation quantity of the lens back of a photographic lens in the range of temperature where the lens is actually used is provided for feeding the lens. Thus, an accurate focal point can be kept in all the range of usage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for correcting lens back fluctuations due to temperature in a photographic lens including a plastic lens.

``Prior art'' Conventionally, plastic lenses have been used in lens systems to reduce costs. However, when plastic lenses are used, lens back fluctuations due to temperature changes are large. The quadrant tends to fluctuate greatly and become out of focus.

Therefore, in general, measures to correct lens back fluctuations due to temperature of plastic lenses include: 1) Reducing the fluctuations in the lens system, 2) Moving part of the lens system or lens barrel to reduce out-of-focus, and 2) Camera. It is conceivable to correct this by extending the AP on the side.

Specifically, the optical system of the autofocus (AP) changes depending on the temperature and corrects the photographing lens back (Japanese Patent Application Laid-Open No. 111223/1982), and the baseline length of the AP changes depending on the temperature. A device that corrects photographic lens backlash by changing the alignment of
-160129), and one that corrects photographic lens back by shifting the distance measurement value by AP using a temperature signal from a temperature detection element etc. (Japanese Patent Application Laid-Open No. 57642).
No. 04) and the like are known.

[Problems to be Solved by the Invention] By the way, the devices disclosed in the above publications all detect temperature and perform lens back correction, and it is possible to perform correction without any problem in the range of temperature or room temperature. However, when the lens is at the (1) position or the closest photographing position and the temperature is outside normal temperature, it is difficult to perform further correction.

The present invention, which changes the amount of aperture of the lens on the camera side, adds a lens stop point that is not used at room temperature outside the lens position Even if there is a temperature fluctuation of more than
Correspondingly, it is an object of the present invention to provide a lens back variation correction device in a camera that compensates for an accurate lens stop point.

[Means for Solving the Problems] The present invention provides a photographic lens including a plastic lens,
In a camera that has a means for detecting temperature and a means for extending the lens for focusing, and is configured to correct lens back fluctuations due to temperature changes of the photographing lens, the closest photographing position is determined from the ω position of the subject. Divide the distance from This is a lens back fluctuation correction device that adds a lens stop point that is selected in response to temperature fluctuations exceeding the normal temperature range outside the position.

[Function] According to the correction device of the present invention, the lens stop point is appropriately determined in response to temperature changes in the room temperature range and subject distance, and furthermore, the lens stop point is located at the (1) position or the closest photographing position. Sometimes, even if there is a temperature fluctuation that exceeds the normal temperature range, a lens stop point added beyond the ω position or the closest imaging position is used in response.

[Example] The main lens system in the first example of the present invention is shown in Figures 1 and 2.
As shown in the figure.

This main lens has a focal length of 35 mm and an F number of 2.6, and the fourth lens is made of plastic. In order to suppress fluctuations in the lens back due to temperature changes as much as possible within the lens system itself, the power of the plastic lens is reduced, or the power is slightly increased in order to make the entire lens more compact and improve its performance.

Therefore, the lens back variation value as a calculated value is the first
The result will be as shown in the table.

Table 1 Here, the amount of lens bar variation at 50°C based on 20°C is 10,08mII+, and -20°C
The amount of variation is in the order of +0.11.

Note that the rate of change in refractive index due to temperature of acrylic polycarphonate, which is the main material of plastic lenses, is -1Oxl.
O-”/'C, (1, tFfj expansion fi 900xlO
'/'C.

Here, we will consider a camera that has a zone focus function that is commonly used in compact cameras. Zone focus assumes an acceptable depth of field,
The focus is divided into several depths of field from ω to the shortest shooting distance. In general, the depth of field d is expressed as u(u−f) δF d=f2±(u−f) δF, where δ is the allowable diameter of the circle of confusion. However, f: focal length, F: lens F
Number, U: Distance from the front principal point to the subject, U represents the front and rear depths.

FIG. 3 shows the relationship between the depth of field of the main lens system shown in FIGS. 1 and 2, the amount of lens extension, and the photographing distance.

In the above lens system, if δ=2×0.033,
Depth of field is 3.62m ~ ■ at 7.2m focus position, 4
．． At 93m focus position, the depth of field is 2.95m to 15.4m.

In this figure, the vertical axis is the amount of feed, and the horizontal axis is approximately proportional to the amount of feed1.
/ Shooting distance is maintained. The mark in the figure represents the focus point. In this example, 1.0 from ω at 14 stop points.
The camera focuses up to m including the depth of field. The depth overlap between the front and rear stop points for each lens stop point is for absorbing AP errors, mechanical errors of the feeding mechanism, and the like.

The relationship between this stop point and the amount of feed is shown in Table 2.

(The following is a margin.) Table 2 (The amount of extension is a value with ω set to 0.) FIG. 4 shows the amount of lens back variation of the main lens system with respect to temperature changes. As shown in the figure, the amount of variation increases as the temperature changes. Therefore, using a temperature detection means, for example, 10
The amount of variation may be corrected by detecting the temperature difference in degrees Celsius and changing the stop point when it exceeds 10 degrees Celsius.

In other words, for example, if the current position is at the seventh stop point, if the temperature difference exceeds 10°C, the system will stop at the eighth stop point. By correcting in this way, a lens back variation characteristic as shown in FIG. 5 can be obtained.

Next, a specific example of implementing the above temperature correction is shown in FIG.

In the figure, 1 is a temperature detection circuit, 2 is a distance detector that detects the distance to the subject, 3 is a lens extension control circuit, 4 is a lens extension device, and SL is a switch that detects the wide-angle state of the photographic lens.

The distance detector 2 divides the distance to the subject into zones 1 to 14 as shown in Table 2 above and outputs the divided distances to the lens extension control circuit 3. The temperature detection circuit 1 outputs a temperature state signal shown in FIG. 9, which will be described later, to the lens extension control circuit 3.

The lens extension control circuit 3 controls the lens extension device 4 with the output of the distance detector 2 when the photographing lens is not in the wide-angle state according to the output of the switch S1. Also,
When the shooting lens is in wide-angle mode, the output of temperature detection circuit 1 indicates that the temperature is below 30℃, -30℃ to -10℃5.
-10°C to 10°C, 10°C to 30°C, 130°C or higher are detected, and the zone signal of distance detector 2 is detected as -
-2 when below 30°C, -1 when between -30°C and -10°C, 0.10°C and 3 when between -10°C and 10°C
When the temperature is 0°C, the lens is shifted by ±2 when the temperature is 1.30'C or higher, and the lens feeding device 4 is controlled by the corresponding zone.

Table 3 shows the relationship between the stop point and the feeding amount in this case.

(Leaving space below) Table 3 As described above, in this embodiment, for the number of zone divisions of the distance detector, an amount corresponding to the amount of variation in the lens back of the photographing lens is provided as an additional lens extension within the actual operating temperature range. , this part is used when correcting based on temperature. This allows you to maintain correct focus over the entire range of use.

A specific example of the temperature detection circuit 1 is shown in FIG.

In this circuit, the element area ratio of transistors Q1 and Q2 is 1:4. As a result, the collector currents of Ql and Q2 are 11.12, the saturation current is i, and the resistance R1 is
If the resistance value of is R1, the absolute temperature is T, and the coefficient is k, then kT 11kT 12-1 n --
−1n −+ I 2 ・R1q i
q 1X4... (1) holds true. Also, if the area ratio of Q3 and Q4 is 4 = 1, the resistance ratio of resistors R5 and R6 is 1 = 4, and the collector currents of Q3 and Q4 are 13 and I2, then K'21n-U+R
5-I3q 1OX4 =K1In Dish R6・I2...(2) i.

or is established.

From the above equation (2), the current ratio between I3 and 12 is 4:1.

That is, from Q3 and Q4, the collector current ratio of Ql and Q2 is 4:1.

The current value that satisfies equation (1) under this current ratio is 1
By substituting 1=4・I2, we get: K work, layer L'' knee, work ln−口− q iOq i

That is, I2 is inversely proportional to R1 and proportional to T. Ql
and R3, Q6 and R4 form a mirror circuit with Q3 and R5, and if R3=R4=4 and Ω, then Ql and Q6 are Q
The current value is the same as 3. Here, the voltage 8 of the terminal E becomes R11X 4 x (kT/) lnie.

Similarly, the voltages V, Vc, and Vs at terminals C and B are as follows:
T )' n 16 , that is, each voltage is proportional to the absolute temperature.

The transistor Q8 is diode-connected, and the voltage across it is:
t.

It is expressed as

Now, if (kT/q) I n16 4 =iM, the temperature coefficient of the voltage V8 at both ends can be calculated as follows (in the room temperature range, there is no big difference even as a constant current.

).

dv8 kkT Ini + (lni)1 kT kT lni n kT Vbe kT (Inα φ/kT) Here, φ 1.21 kT 4.1x 10'-T Ce V) 1.21 4゜IX 10-4 ni 1 n α 10kT kT 1.21 (Inα-φ/kT) = kT kT Vbe kT 1.21 Vbe-1,21(
v /, c) T q kT2 T Now, if Vbe at room temperature is about 700 nunV, the temperature coefficient of both voltages of Q8 is -1.7 mV/'C, which has a negative slope with respect to temperature. becomes (vA).

FIG. 8 shows the temperature coefficient of each voltage mentioned above.

The above V straight line and V8, V c , V D, V E
-30℃, -10℃510℃130℃ respectively
Resistors R8, R9, R10, R11, R1 so that they intersect at
2. If R13 is set, each temperature can be detected.

R12 and R13 are resistors that are adjusted so that the straight lines of the temperature coefficients of the respective voltages intersect at a fixed point. Q5 is a transistor for starting this circuit, and R7 and R2 are resistors that limit the current flowing through this transistor Q5.

By connecting the comparators C1 to C4 to the circuit with the above configuration as shown in Fig. 7, the Ht or L data shown in Fig. 9 can be obtained at the output, thereby detecting the temperature state. can do.

10 and 11 show a second embodiment, which includes a 1m-th main lens L and a second group rear converter lens RC. The main lens system of the first group is the same as the main lens system of the above embodiment, and behind it is the rear converter lens R of the second group.
C is attached to form a tele system. Focusing in this state is often performed using only the first lens group.

In this lens system, the lens back variation amount of ÷30° C. varies depending on the amount of extension, and is as shown in Table 4.

(Margin below) Table 4 Even for such a lens, in this example, as is clear from the above explanation, the temperature and distance information based on AP can be obtained separately as parameters, so the analogy is valid. In terms of temperature, it is possible to deal with objects at a distance of 1 m or more by setting the stop point to one stop point on the far side.

[Effects of the Invention] As described above, according to the present invention, in a camera having a photographic lens including a plastic lens, it is possible to correctly select the lens stop point in response to temperature fluctuations within the room temperature range. Of course, even if the temperature fluctuates beyond the normal temperature range when the lens is at the ω position or the stop point of the closest photographing position, the temperature will be added to the outside of the ■ position or the closest photographing position correspondingly. The correct lens stop point is selected using the lens stop point that was
It becomes possible to take photographs with correct focus over the entire temperature range, even at the ω position and the closest position.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a main lens system according to an embodiment of the present invention;
Figure 2 is a diagram showing the specifications of the lens, Figure 3 is a diagram of the relationship between the depth of field and the amount of extension of the main lens, Figure 4 is a diagram of the relationship between temperature and lens back variation, and Figure 5 is a diagram of the actual implementation. FIG. 6 is a block diagram of the specific configuration of this embodiment, FIG. 7 is a circuit diagram of the temperature detection circuit, and FIG. A diagram showing the temperature coefficient of each voltage in the circuit, Figure 9 is a diagram showing the relationship between the output of the circuit and the temperature state, Figure 10 is a configuration diagram of the lens of the second embodiment, and Figure 11 is the specification of the lens. FIG. Main lens, 1... Temperature detection circuit, 2... Distance detector, 3... Lens extension control circuit, 4...
Lens feeding device.

Claims (1)

[Claims] (1) It has a photographic lens including a plastic lens, a means for detecting temperature, and a means for extending the lens for focusing, and is adapted to correct lens back fluctuations due to temperature changes of the photographic lens. In the camera, the distance from the ∞ position of the subject to the closest shooting position is divided into multiple zones, and a lens stop point is set for each zone depending on the temperature change within the room temperature range and the subject distance. , Lens back fluctuation correction in a camera, characterized in that a lens stop point selected in response to temperature fluctuations exceeding the normal temperature range is added at the ∞ position of the lens stop point or outward from the closest photographing position. Device.