DE1888415U - Photoelectric light meter with variable angle of view - Google Patents

Description

Photoelectric light meter with variable angle of view

The innovation concerns a photoelectric exposure meter, the angle of view of which can be changed.

Such exposure meters per se already belong to the state of the art. The change in the angle of view can result done different ways. So it is known, for example, before the radiation receiver of the light meter Switch varifocal lens, which one depends on its setting a more or less strong concentration of the radiation receiver caused by a striking stream of light.

Another known possibility is in front of the radiation receiver set an aperture that reduces the angle of view of the Light meter determined. If this aperture is reduced, the solid angle of the is inevitably also reduced Radiation receiver detected luminous flux.

Other known means for changing the angle of view are tube diaphragms of different lengths, which can be selected after optional insertion

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result in a certain angle of view in front of the radiation receiver. A variant of this type of solution consists in that a diaphragm which can be displaced along the optical axis is arranged in front of the radiation receiver of the exposure meter built into a camera that is associated with the device for changing lenses or is coupled to the device for adjusting the focal length of a lens with a variable focal length that the The angle of view detected by the lens coincides with the angle of view detected by the radiation receiver of the exposure meter.

Since when the angle of view is changed, the entire the luminous flux hitting the radiation receiver is changed, incorrect measurements arise if care is not taken that at the same time as the change in the angle of view of the the light flux impinging on the radiation receiver is compensated in this way is that it remains constant despite changing the angle of view.

This fact is taken into account in known devices borne that, for example, the radiation receiver is assigned a further aperture, which when the angle of view is reduced and associated reduction in the luminous flux is increased to the extent that the on the radiation receiver incident luminous flux remains constant. This solution shows the The disadvantage is that only large-area radiation receivers, e.g. selenium elements, can be used.

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Other known ways to compensate for the luminous flux consist of neutral density filters or other light attenuating agents to switch in front of the radiation receiver or in the photocell circuit to provide an adjustable resistance.

Compared to these known devices, some of which are very expensive and some of which are only used then can, if there are relatively large-area radiation receivers ^ the task of the innovation is to use the simplest means to create a compensation option for the luminous flux hitting the radiation receiver, which also the use of extremely small radiation receivers, e.g. cadmium sulfide resistors, is allowed.

With a photoelectric exposure meter, which by means of a variable aperture in front of the radiation receiver on different Angle of view can be adjusted and what means has the- to compensate for the greater by the adjustment or decreasing luminous flux reaching the radiation receiver, this task becomes according to the innovation solved in that with the slide, as a carrier for the Radiation receiver, connected to a pin, which is inserted into the Control curve of the component engages, the component serving in a manner known per se as an actuator for the iris diaphragm and the position of the radiation receiver relative to the variable Aperture or one of these associated optical means (e.g. a ground glass) with the adjustment of the aperture is changed so that the geometric flow of the

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Radiation receiver incident luminous flux remains constant.

According to a further feature of the innovation, it is kept constant the geometric flow of the luminous flux by changing the distance of the radiation receiver from the aperture or from the associated optical means.

In deviation from this type of solution, keeping the geometrical flow of the light stream according to another The feature of the innovation, however, can also be achieved by rotating the radiation receiver in such a way that its normal no longer exists coincides with the optical axis.

Further details of the innovation can be found in the following Description of two exemplary embodiments and the associated ones Drawings and the claims for protection. In the Drawings show:

Fig. 1 is a schematic representation of the device according to the innovation in side view,

Fig. 2 a representation of the relationships, which serves to understand the measure according to the innovation,

Fig. Β the side view of two different designs and h

examples of the innovation, partly in section i

According to Fig. 1, a radiation receiver E is arranged on the optical axis of the lens consisting of the two lenses 1 and 2, to which a measuring mechanism h or an automatic diaphragm is connected in a known manner via a power source 3.

Between the objective 1, 2 and the radiation receiver E is a per se known diaphragm B is provided, the passage opening of which can be changed. Located in the immediate vicinity of the aperture B. an optical means, e.g. a ground glass M, which causes the uniform illumination of the entire illuminated area.

The lens consisting of the two lenses 1 and 2 can an adjustable diaphragm 5> for example an iris diaphragm, which represents the aperture diaphragm of the objective. By adjusting this aperture, filter factors or different exposure times can be taken into account. aside from that through the aperture 5 different initial openings of Interchangeable lenses are taken into account.

The angle of view of the exposure meter is determined by aperture B certainly. In order to get an exact To obtain the measurement result, the radiation receiver E must be arranged at a certain distance from the optical means M, i.e. that when the diaphragm B is reduced, the distance e also must be made smaller. Both changes must. In such a

lawful interdependence can be made that the luminous flux striking the radiation receiver E remains constant.

With regard to Fig. 2, the following relationship arises for the luminous flux;

^{B d} % ^ B cos £ -J ^ = ■ const.

Ml

As can be seen from Fig. 2, df ^ and df _{E represent} surface

elements of M and E, <£ _M and c _E are the angles between the normal η and the connecting line r of the two surface elements df «and df ™. Pa <£ _M and <p ™ are equal to each other, the angle appearing in the above formula is £ = £ _M = <5g ·

Φ
If one sets G »-§- then G is the geometric flow and it must hold; G = f (M, e), d, h. if M changes, e is to be changed in such a way that G = const. is satisfied.

In practice, the optical means M is not an ideal cosine emitter be as assumed in the formula. That's why the change in distance from e becomes somewhat modified Function depend on the size of the effective area M,

To increase the sensitivity of the light meter, M can be designed so that its scattering angles are very small and the tufts only cover the displacement of E. ^B ine white

Another improvement would be the use of a field lens in the Level of M yield.

A practical embodiment of those described above The possibility of compensation is shown in Fig. 3. The diagrammatically shown iris diaphragm B is known and therefore not In the manner explained in more detail, mounted between a fixed ring 6 and a rotatable component 7. As a carrier for the radiation receiver E a slide 8 is provided, which by means of screws 9 and 10 on a fixedly arranged in the component 7 protruding arm 11 is slidably mounted. In the component 7 a control cam 7 a is provided, in which a with the slide 8 connected control pin 12 protrudes.

When the aperture B for the purpose of changing the angle of view is to be adjusted, this is done by rotating the component 7, which at the same time causes the slide 8 and thus the radiation receiver E as a result of engagement of the control pin 12 in the control cam 7 a experiences a movement in the direction of the optical axis. The control cam 7a is designed so that the conditions described above with respect to the distance of the Radiation receiver E are met by the optical means M at any setting of the diaphragm B.

Another possibility for comparing the luminous flux hitting the radiation receiver is shown in the exemplary embodiment according to FIG. * F. Here wild the distance of the.

Radiation receiver E by the optical means M is not changed. Rather, the radiation receiver E is rotated to compensate for the adjustment of aperture B so that its. Normal no longer coincides with the optical axis. The constant luminous flux φ is achieved in that <3w is different from <£ _ ,.

As can be seen from Fig. K , the screen B is also mounted here between a fixed ring 6 and a rotatable component 7 '. A rotatable disk IM- is arranged on a fixed arm 13 which projects into the component 7 'and serves as a carrier for the radiation receiver E. A pin 15 firmly connected to the disk lh protrudes into a control slot 7 a ^{1 of} the component 7 ^f . A tension spring 17 'which is hung with one end in the pin 15 and with its other end in a pin 16 firmly connected to the arm 13, ensures that the pin 15 is in constant contact with an edge of the control slot 7a *.

The setting of the diaphragm B for the purpose of changing the angle of view is also done in this embodiment by rotating the component 7V »which at the same time has the consequence that the disk I ^ and thus the radiation receiver E as a result of the engagement of the pin 15 in the control slot 7a 'according to the Slope of the control slot 7 a ^{1 is} pivoted. The control slot 7 a ¹ is designed so that in each case a pivoting of the radiation receiver E takes place to such an extent that the luminous flux is maintained constant.

Claims (3)

Protection claims 1. Photoelectric light meter, which by means of a variable aperture in front of the radiation receiver on different The angle of view can be adjusted and which has the means to compensate for the adjustment larger or smaller luminous flux reaching the radiation receiver are suitable, characterized in that, that with the slide 8, as a carrier for the radiation receiver E, a pin 12 is connected, which in the Control cam 7a of component 7 engages, component 7 serving in a manner known per se as an actuator for iris diaphragm B and the position of the radiation receiver the variable aperture or one of these associated optical means (e.g. a ground glass) with the adjustment the diaphragm is inevitably changed so that the geometric flow of the incident on the radiation receiver Luminous flux remains constant. 2. Exposure meter according to claim 1, characterized in that that keeping constant the geometric flow of light Current by changing the distance of the radiation receiver from the diaphragm or from the one assigned to it optical means by the inevitable displacement of the slide 8 via the pin 12 by means of the control cam 7 a he follows. - 10 - 3. Exposure meter according to claim 2, characterized in that by changing the aperture B by means of the Component 7 »connected with the inevitable change in position of the slide 8, the change in the distance of the radiation receiver E on the diaphragm or on the optical means M assigned to it in such a regular dependence be made from each other that for the luminous flux approximately the following relationship applies: (T) = J j B df _M df _E cos ^ £ -γ- = const., ^ ME ^e where with df «and dfg surface elements of M and E, with e the distance from E to M, with B the illuminance in the diaphragm plane and with <5 the angle between the normal η and the connecting line of the two surface elements df «and df ™ are designated. H. Exposure meter, characterized in that a disk Ik- serves as a carrier of the radiation receiver E, which is rotatably mounted on an arm (13), the disk (I ¹ O via the pin (15) by means of the curve 7 a * simultaneously with the Change in position of the component 7 ^{f is} rotated when adjusting the iris diaphragm B, so that the geometric flow of the luminous flux is kept constant by rotating the radiation receiver in such a way that your normal no longer coincides with the optical axis. - 11 - 5 · Exposure meter according to claims 1 to ^ f or one
or more of the same, characterized in that the
The entire system is preceded by an aperture diaphragm (5), which can be adjusted to different initial openings of
Interchangeable lenses and / or filter factors and possibly different exposure times can be taken into account.