DE1797575B2 - Focusing device. Eliminated from: 1422563 - Google Patents

Description

The invention relates to a focusing device for optical instruments having an in image space a photoelectric converter arranged in a focusing lens system, its resistance when focusing of the image on the transducer surface au. verist.

As is known, the photocurrent of a photoelectric converter increases with increasing illuminance /, which is equivalent to a corresponding decrease in the internal resistance R of the converter. This relationship can be expressed by the general formula

R =

I ' where k and e are material constants of the respective transducer.

This general relationship is not only obeyed by vacuum photocells, gas-filled photocells, barrier photocells, but also the photoconductive cells known as semiconductor photoresistors, e.g. B. CdS cells.

If an object is imaged on a certain plane with the aid of an imaging lens system, then has the designed image in the in-focus case has the smallest dimensions, and they are essential here Differences in illuminance and brightness distribution compared to the blurred image of the same object present. One should therefore expect this fact to turn into a somehow type of change in the internal resistance of the converter.

In a focusing device of the type described above known from German patent specification 709 954, the image generated by the optical system is projected onto a photocell for this purpose, which shows a non-linear relationship between the photocurrent and the illuminance, i.e. a curved characteristic curve (e does not equal I. ). whereby the degree of sharpness of the image can be deduced from the size of the photo current and the setting of a system can be recognized without looking at the image. As eligible for this

Photocell types with curved characteristics (e less than 1) are called barrier photowells, gas-filled and high-vacuum cells. The former show curved characteristics when they are connected to external resistances that are roughly in the order of magnitude of the internal resistance of the cell or above. The latter cell types also show saturation of the photocurrent at higher illuminance levels and thus a curvature of the characteristic curve. Here it was recognized that the greatest change in current or change in internal resistance occurs when the photo cell characteristic curve for the average illuminance of the image has the greatest curvature, while on the other hand in the linear characteristic curve range (e = 1) there is no such current or at all Internal resistance change occurs. However, since the average brightness of the individual images can be very different, it is to be expected that in many cases the operating point on the photocell characteristic will fall within the linear range of the same, so special circuit measures are necessary in order to achieve a desired change in the photocurrent transition from fuzzy to sharp setting. For this purpose, two ways are basically provided in the known arrangement, namely (1) artificial distortion of the entire characteristic curve to obtain a curved course with the help of suitable distortion circuits that are connected between the photocell and the display element, and (2) provision of an automatic control in the Meaning that the working point on the characteristic curve is always relocated to an area of the greatest curve curvature.

These measures are obviously cumbersome and, moreover, by no means always lead to a large, detectable measuring range in the sense of a strongly fluctuating, average brightness of the image to picture. For example, if one looks at a characteristic curve that is uniformly curved from the zero point, the finally turns into a horizontal straight line (saturation area), so images above a corresponding average brightness can no longer be detected. You want these cases anyway still grasp, an appropriate art circuit would have to ensure that the horizontal running characteristic curve branch comes to lie higher. However, this automatically reduces the curvature in the usable range of the characteristic curve. which in turn comes at the expense of sensitivity.

In the case of barrier photocells (copper-copper oxide cells and selenium cells), the electrodes are generally used formed flat and close like a capacitor a dielectric, between them the copper oxide or selenium, whereby one of the two electrodes LichtduL is designed to be permeable. That on this The light incident on the electrode sets in the layer underneath at an observed point Due to the internal photo effect, electrons free their number from that prevailing at the starting point Illuminance depends. In this type of Electrode arrangement are therefore always next to each other lying surface elements fell from an electrical point of view behave as if their assigned opposing elements are connected in parallel also applies to a vacuum or gas-filled photo / rush, for which ai due to the external photo effect Illuminated parts of the folocathode surface

Tronen escape and because of the pending Saugspaniuing be transferred to the anode. Here, too, the partial gaps under consideration add up the partial siren emerging from the kiithode surface, see above that in effect there is also a parallel connection of the individual surface elements.

On the other hand, the conditions are completely different for those known as semiconductor photoresistors foioleitfahigen cells, which on two opposite Front edges of a photo semiconductor layer are provided with the necessary connection electrodes. For the sake of simplicity, it should be assumed here that these electrodes are along the entire extension these front edges run. If, for example, one half of the folo resistor is now illuminated, then so one obtains (regardless of whether the cut-off line is sharp or fuzzy) an electrical one Parallel connection of the partial resistances assigned to the dark or the light half, if the cut-off line runs perpendicular to the electrodes, but a series connection of the same if the cut-off line runs parallel to the electrodes. 1 η the cases in which the cut-off line is sloping runs, the effect is a combination of partial resistances connected in parallel and in series.

Attempts have been made to replace the photocells with more modern semiconductor photoresistors. As beneficial It turned out that semiconductor photoresistors inherently have a curved resistance-lighting characteristic exhibit. So there are no circuit tools or saturation mode required, such as it is the case with the above-mentioned German patent specification.

However, it has been found that the semiconductor photoresistor has two opposite end edges arranged connection electrodes does not allow any measurement definable for focusing. This is because the resistance that can be measured when the focus is set depends, among other things, on whether the cut-off line of the object to be measured is perpendicular, parallel or inclined to the electrodes. That means z. B. that when panning the camera around the lens axis for a stationary object, the resistance value changes when the focus is adjusted while panning or that there is no defined one for moving objects Measurement is possible.

It is therefore the object of the invention to provide a focusing device of the type described at the outset to make, which allows a defined measurement of the focus condition at any time.

According to the invention, this object is achieved in that a semiconductor photoconductor is used as the converter is provided. whose photoconductor layer is divided into a plurality of sections by partition walls is and that the partitions are designed in a known manner as electrodes, wherein the Determination of the in-focus condition from the entirety of the segment output signals.

One advantage of the invention is that the electrode arrangement has a large number of sections the photoconductor layer is connected in parallel, so that the entire semiconductor component has a low Has internal resistance. This results in the possibility of using the one for the focusing device semiconductor component used to carry out an exposure measurement at the same time.

Ali's equation (I) can be seen that the resulting Change in resistance at a given

leuchtungsstärkeänderung, so the sensitivity will be the greater, the greater the Wen e. As mentioned, in the known focusing device, the presence of a curved line shape corresponding to an e value less than 1 is an imperative. According to the invention, the characteristic range for which e> 1 can also be used. It is therefore not only possible to enlarge the detectable measuring range, but also to achieve a higher sensitivity with the arrangement according to the invention.

F i g. 1 shows a schematic representation of a focusing device, the light-dark boundary of the object is vertical,

FIG. 2 shows the focusing device according to FIG. 1. however, the cut-off line of the object runs horizontally,

F i g. 3 and 4 an embodiment according to the invention of a photoresistor with He ¹ !

F i g. 5 and 6 illuminance distribution curves in the image plane of the device according to FIG. 1 with a sharp or unsharp image and

F i g. 7 is a schematic representation of a display circuit with a semiconductor photoresistor.

According to FIG. 1, an objective lens 1 is displaceable in both directions along the optical axis arranged. A photoresistor 3 is located in its focal plane 2. There is also an electrical power source 4 and one in the circuit; 5 horizontal galvanometer 6 is provided.

For the explanation it is assumed that the object P to be imaged consists of a light and a dark half (shown hatched in FIG. 1) and that the light-dark boundary ρ intersects the optical axis. The object P with its light-dark boundary ρ is on the. Photoresistor 3 shown as image P ' with a corresponding light-dark boundary p' . The distribution of the illuminance in the image plane will therefore have a pronounced step in the case of focusing (curve C in FIG. 5). while in the case of a blurred image there will be a gradual transition (curve C ″ in FIG. 6).

In Fig. 2 is the same arrangement as in Fig. 1 shown. While in FIG. 1 the cut-off line runs vertically and thus parallel to the electrodes of the photoresistor 3, it is in FIG. 2 horizontal and thus perpendicular to the electrodes of the photo resistor. In general, the partial resistance in the dark area of the photo resistor is a multiple of the partial resistance in the light area of the photo opposition. In the case of F 1 and 1, the high dark healing resistance and the low high-temperature resistance are interconnected. so that the total resistance of the folo resistance is essentially by. the dark resistance is formed. Since in the case of FIG. 2 dark and light partial resistors are connected in parallel to one another, the total resistance of the photoresistor is essentially formed by the low partial resistance Heii. With a constant difference in brightness / between the dark and the wholesome area, the total resistance of the folo resistor 3 and thus the measured value on the measuring device 6 is completely different depending on whether the HcII-Dunkcl level runs horizontally or vertically. If the camera moves around its lens axis while the object is stationary, the door changes

I 797

Distance setting measured value to be evaluated The the same applies to a correspondingly moving object. It is therefore not a clear measurement for Purpose of distance adjustment possible.

The present invention achieves that. ^: regardless of whether the Hll-Dunkcl-size runs horizontally or vertically, there is always a parallel connection of dark and light partial resistances. 3 and 4 it can be demonstrated that a photoresistor, which is divided into a plurality of sections by partition walls. shows a measured value that is practically independent of the position of the Heil-Dunkel-Grenzc.

Since the object to be photographed is generally placed in the center of the image, it is reasonable to assume for the calculation that the cut-off line is practically in the center of the photo resistor. In FIG. 3 it is assumed that this boundary runs parallel to the partition walls designed as electrodes, while in FIG. 4 is perpendicular / un the partition walls. Inclined Hcel-Diinkel lines can be viewed as a combination of these two cases.

First of all, let the case according to FIG. 3 considered. The resistance layer between two dividing walls can be: If one assumes that there is a contradiction between each pair of electrodes. then _K

^D parallel ^H parallel '/>+' //. (I)
/ il HI 2 2

from which the following total resistance results:

ID ... IH
parallel .

if one assumes a dark resistance that is only 10 times as large as the light resistance, this difference is only a maximum of 7%. However, these values are within the accuracy of reading in the case of the galvanometers commonly used for cameras. In addition, this measured value deviation will only cause the objective to be incorrectly adjusted so that the object to be imaged is still in the depth of field. If the field of focus of the lens used is small, the measured value deviation can be reduced by increasing η. For example, with 50 resistance paths between 2 electrodes each, the result is a dark resistance that is 100 times greater than the light resistance. a weight difference of less than 2%.

In the diagrams of ⁷ F ig 5 and 6, the Bc-IcuchUingsstäikcverleilimg C and C, respectively is located hei sharp or blurred image in the image plane for the considered example results, plotted with the illuminance / as ordinate. For s \ mmetric reasons, the ordinate Ix = 0) of the coordinate system used is relocated to the cut-off line / '. The illuminance of the dark part of the picture surface is assumed to be / ,,. that of the light part ¹ - denoted by /, and the relationship of this to that with in : it is therefore true

/ ,. - ml ,,: with in > I. (2 |

If, on the basis of FIGS. 5 and (■ at. that the illuminance / at places outside the coordinate origin at χ and -χ / (x) and / (- x) is. results in the case of FIG. 3

2 · D ■ H (D 4 / M (I 4- H) - (D- + // ^: 4- I) ■ H) '

In the case of FIG. 4. that the Hcll-Dimkd-Grenzc runs vertically and in the middle of the photovoltaic area, results for each resistance section a parallel connection of a dark and a high-level resistor. Now applies here

(IU) from which the following total contradiction results:

7th f-l ■ Τ)

* «··> ⁼ njH ~ + ~ Dj- ^{(IV |}

For the following calculation example, η is assumed to be 19, ie 19 resistance paths between each pair of electrodes. One accepts. that the dark resistance D is 100 times as great as the HcII resistance H , it follows in the case of FIG. 3 a total resistance of 0.099 H, in the case of FIG. 4 a total resistance of 0.104 H. Depending on whether r «; the cut-off line runs parallel or perpendicular to the partition walls, so the difference in the total resistance is a maximum of 4.8%. Self = I _h

and for F i 2. 6

I (x) = I _h - h1 _d or because of i2) -! Jni - / :)
/(-.v) = / ,, - hl ,, = / ,, (1 - / 1) (4)

with the one from FIG. 6 apparent meaning for / 1

Let it be in FIG. 7 shown FjII considered in which the light-dark limit / j 'is the image on the photoconductive cell parallel to the direction of the semiconductor body s current flowing. The total resistance of the photoresistor is here a parallel connection of individual resistances r of many successive small strip elements, which are assumed to be between the two electrodes.

If one considers the resistance elements r at the points χ and -x as a unit, i.e. as a parallel connection and denotes the total resistance of the same with a sharp setting with r (- x. X) and that with a fuzzy setting with r '(- x. X), after a few intermediate calculations, the expressions for these quantities result from equations (1) to (4)

(1 4-

(5a)

] 1 1 and Pur blurred setting

r '{- x, x) / k \ / k_

5 R '

_ -ί5_Γ (ΐ -ι- hf + (m - / i) H (5b) From equations (9) and (10) it follows that the

k sign of magnitude

IO

To calculate the change in resistance / 1 at
a transition from unsharp ευ sharp setting l / R '- l / R (11)

the equations (5 a) and (5 b) are to be subtracted:

is determined by the sign of / I. The Pro

. is a sign of .1 but depends on the size e . how

(6) This is determined by the formula (8). So you have

r '(- x, x) r ( x, x) three cases to be distinguished:

_oc j _er a) Fürt '> 1 becomes! <O; so - ^ r <- ^. (12)

I ₌ II [(j ₊ h) - + (m - hf - (1 + m *)] * (7) b) For e = I, .1 = 0; so - ^ r = - ^ -. (13)

c) For <1, .1>0; so - = r> - = -. (14) It can be shown that the sign of I is given by ^{K K}

the quantity ₂ , It therefore follows that the electric current in the

photoconductive cell in the focus trap

(1 - m ^c ~ ^x ) (8) The maximum is when e> I, that it is independent of the degree of focus when c = 1, and is determined. that it is a minimum in the case of focus.

In the example under consideration according to FIG. 7 results in 30 if e < 1.

Therefore, for the total resistance in sharp focus, e is between C.

position casec ^{ur |} d 1 · On the other hand, it must be pointed out that Zeller

with e> 1 with respect to the increasing with e

1 _ ^ -— 1, Q, sensitivity are most desirable. The size

~ jC ~~ 2.— _r (_.x, χ) 35 ße e should be made significantly different from 1.

1 sheet of drawings

Claims (1)

Claim: Focusing device for optical instruments, with a photoelectric converter arranged in the image space of a focusing lens system, the resistance of which has an extreme value when the image is in focus on the converter surface, characterized in that a semiconductor photoresistor is provided as the converter, which has a slope of e Φ 1 and its photoconductor layer is divided by partition walls into a plurality of sections, and that the partition walls are formed in a manner known per se as electrodes, the determination of the focus condition being obtained from the entirety of the section output signals.