WO1985000062A1

WO1985000062A1 - Apparatus for controlling the flash lighting in macrophotography

Info

Publication number: WO1985000062A1
Application number: PCT/CH1984/000093
Authority: WO
Inventors: Christo Obreschkow
Original assignee: Christo Obreschkow
Priority date: 1983-06-16
Filing date: 1984-06-12
Publication date: 1985-01-03
Also published as: EP0145743A1

Abstract

The apparatus comprises a macrosystem (2, 3) cooperating with a photographic camera (1), preferably formed of a macroconverter (2) and of a normal lens (3); in the macrosystem there is provided a light sensitive element (5) directed to the film plane (7) in order to control a flash (15) provided to this effect and correspondingly synchronized. The photosensitive element measures the object light (Ar') reflected by the film plane with a set angle beta, whereas the controlled flash may be arranged in the desired shadow angle alpha. Thereby, with a small technical investment, it is possible to transform an interchangeable lens photographic camera available in the market into the most modern camera usable in macrophotography.

Description

DEVICE FOR CONTROLLING FLASH EXPOSURE IN MACRO RECORDING.

The invention relates to a device for controlling the exposure of objects in macro shots, consisting of at least one electronic flash device and at least one photosensitive element which controls this flash device.

Macro photography is a problem area of. fundamental importance, namely the mutual relationship between the object illumination and the extremely significant depth of field. On the one hand, the depth of field depends to a certain extent on the aperture opening, but on the other hand it also depends on the object distance, which object distance is limited to the macro range in macro photography and as a result of which the depth of field is subjected to the same limitation.

Shallow depth of field creates not only in depth, but also peripherally blurred images with a striking loss of detail, and it can be viewed in a transferred way can be said that the photographic quality in macro photography is directly proportional to the (achieved) depth of field. This applies to most applications.

The depth of field is fundamentally limited by the geometry of the optics and the selected object distance. As the variable size influencing the depth of field within the optical system, only the aperture is responsible. In the case of flash photography, this aperture is ultimately dependent on the sensitivity of the film material and the intensity of the object light.

Photographic equipment for macro photography only meets these and the following requirements to a limited extent. For example, special brackets made it possible to arrange artificial light sources, lamps, electron flashes, etc. directly next to the front lens of the lens in order to at least avoid camera and lens shadows on the illuminated object. Since the required angle of incidence depends on the photographic working distance and the position of the light source in turn influences the intensity of the object light, working in the macro range requires constant adjustment of the light source. Since the aperture is empirically set due to a lack of measurement options, the quality of the photographic results with such combinations of apparatuses for obtaining macro pictures is quite inconsistent.

In order to avoid these difficulties, ring flash tubes were created, for example, which lens of the lens. A new disadvantage of the same is obvious: Although very reliable, reproducible exposures can be achieved with ring flash units, the surface structure is leveled by the 360-degree shadow and thus loses detailed information. In addition, the light intensities that can be achieved with ring flash units are relatively weak, which requires a larger aperture, which immediately reduces the depth of field.

It has also become known to equip flash units with electronic light sensors in order to enable quantitative light control. Electronically controlled point light sources they were known under the name computer flash show a lighting characteristic that allows the surface details to be produced much better than is the case with the previously mentioned ring flash. In addition, the electronic exposure control enables the macro to work with constant aperture values. This allows the depth of field to be fixed; the light accumulation should ensure a sufficient intensity of the object light.

This creates new problems in the difficult and demanding field of macro photography. With sensor-controlled flash light sources, it is not possible to point both the flash window and the photo sensor at the same point on the object in the case of small object distances. This is particularly the case when pictures of objects that are lowered or lowered in relation to the surface or even hidden in caverns or caves should be taken. For example, reference should be made to the problems of professional medical and dental photography, with recordings in body cavities during surgery or with photography in the oral cavity. The exposure control of a macro-photographic system, i.e. camera, macro device and artificial lighting, must consequently be based on the amount of light incident on the film level in order to determine the amount of light for adequate exposure of the film material from this information. In this case, the required reproducibility, roughly speaking, would be guaranteed. Such film plane measurements are known in connection with various photo systems in which the film plane is photo-sensor-monitored for preconditioning the exposure control and for correcting the exposure time (for example) during the exposure process. With this control system it is possible to reproduce the photon energy integral quite well, regardless of the angle of incidence, type of lighting, optical systems, etc.

This difficult and complex exposure control has so far been implemented in various camera systems and in each case relates exclusively to the camera itself, and in particular accessories desired from outside the system cannot be combined, particularly for the macro photography that relies on this exposure methodology.

It is an object of the invention to provide a device with respect to macro photography which enables known camera systems with interchangeable optics to be brought up to the current state of the art in macro photography. Furthermore, it is an object of the invention that the device to be created simplifies the macro photography in the apparatus area and can be used together with commercially available devices in the sense of an accessory. The task is solved in that a photosensitive element in the edge region of the beam path between the imaging optics of a macro system and the image plane of a camera is arranged so that it can be removed from the camera and can be electrically connected to a flash unit.

With the help of the figures below, an embodiment of the invention is discussed in detail. It shows:

FIG. 1 shows a macro-photographic arrangement with the device according to the invention,

FIG. 2 shows a functional detail in connection with the macrophotographic light measurement,

Various tools are available in macro photography to achieve small image scales. Lens attachment lenses and spacer rings, which are connected between the camera housing and the lens, are simple and relatively cheap, but they quickly lead to limitations in the imaging scale. Such restrictions on the imaging scale can be avoided by using variable extracts between the camera and the imaging optics; such extracts are adjustable tubes (telescopes) and bellows devices. A further possibility is offered by the macro converter, as described for example in DE-PS 25 45 953 by the applicant, with which the loss of light is minimized with an extremely short overall length, with a continuous change in the imaging scale up to 1: 1. Such a macro converter was chosen for the macro system which basically according to Figure 1 comprises a camera 1, said macro converter 2, a normal lens 3 and a flash unit 15.

Furthermore, one can see in FIG. 1 an optical axis 9 running through the optical system for the macro system 2, 3, a second optical axis 15 'inclined to the first for the illumination source 15, that is to say the flash unit, and a third optical axis likewise inclined to the first Axis 5 'for a photosensitive measuring element 5 in the macro converter 2. In the extension of the optical axis 9 of the macro system 2, 3 there is an object 13 with an object relief 13' to be imaged, which object relief lies in the light cone 17 of the lighting or flashing device 15 is illuminated by a luminous flux A. The lighting device is, for example, an electronically controllable flash unit and, for the sake of simplicity, is only functionally represented by a flash window 20 in a black box 15. An electrical connection 1 serves to transmit the measured value from the macro converter 2 or its photosensitive element 5.

The light AR reflected by the object relief arrives along the optical axis 9 of the macro system through the lens group 3 'of the objective 3 and the lens group 2' of the macro converter 2 onto the film plane 7 in the camera 1. That which runs along the optical axis 5 'of the photosensitive element 5 "Light AR 'reflected from the film plane is measured by this photosensitive element 5 and the measured value is processed in a circuit associated with a photodiode but not shown, for example, and supplied to the flash electronics (also not shown) via electrical connection 14. This measured value determines the duration of the electronic additional light to the existing object light, ie it completes the required proportion of the exposure energy. While the optimal angle β between the optical axis 9 of the macro system and the optical axis 5 of the photosensitive element is determined empirically, the angle α between the optical axis 9 of the macro system and the optical axis 15 'of the flash device is arbitrary, for example solely on the imaging requirements or related to the spatial possibilities, selectable.

FIG. 2 now shows a problem which has already been indicated at the beginning, namely the macro shot with computer flashes and the associated parallax problem. A light source, here again a flash device 15 with a flash window 23 and a permanently installed light sensor 5, illuminates the relief 13 'of an object 13 within the light cone 17. The optical axis 15' of the flash light source stands at the desired illumination angle to the object, from which a number of arrows are shown, diffuse light is emitted after several seitan. A part Am of this light strikes the light sensor 5, another part AR finally falls as object light via the lens 3 onto the film plane 7. The reflected light in the direction Am and the reflected light in the direction AR differ more strongly, the larger the with γ designated angle between the optical axes 5 'of the photosensor and 9 of the macro optics. The relationship AR = k. AM occurs when the light is measured along the optical axis 9 of the macro system, where k ~ i or as reflected light from the film plane, under which condition k << 1 can be obtained, but the linear relationship is retained. This is the case in the arrangement according to the invention, as shown in Figure 1. In the extreme case, it can happen in the arrangement of FIG. 2 that the optical axis 5 'of the light sensor 5 no longer strikes the object 10, which leads to the light sensor instead of the object light changing Light impression from the surroundings. Of course, this leads to incorrect exposure.

The macro photo device thus consists of a commercially available camera with an interchangeable lens and an electronically controllable flash unit that is tailored to the macro range. The macro system equipped in accordance with the invention has the commercially available bayonet and screw couplings and is equipped with the indispensable automatic aperture control. The macro range typically extends from 1:10 to 1: 1 without changing the overall length, whereby this overall length is also extremely short. The entire working area of the optical system can 1:

up to 1: 1. This means that with the application of the invention, a commercially available interchangeable lens camera (mirror reflex camera) of a younger or older design and regardless of the price category is upgraded to a macro device in the currently most advanced state of the art with relatively little effort.

Claims

PATENT CLAIMS

1. Device for controlling object illumination in macro shots, consisting of at least one electronic flash device and at least one photosensitive element which controls this flash device, characterized in that the photosensitive element (5) in the edge region of the beam path (9) between imaging optics (3) of a macro system (2, 3) and image plane (7) of a camera (1), which can be removed from the camera (1) and can be electrically connected to a flash unit (15).

Device according to claim 1, characterized in that the macro system (2, 3) consists of a macro lens and the photosensitive element (5) is arranged in the macro lens.

3. Device according to claim 1, characterized in that the macro system (2,3) consists of a normal lens (3) and a macro converter (2) and the photosensitive element (5) is arranged in the macro converter (2).

Device according to one of claims 1 to 3, characterized in that the optical axis (5 ') of the photosensitive element (5) with the optical axis (9) of the macro system (2,3) includes an angle of 33 to 60 degrees.

5. Device according to claims 2, 3 and 4, characterized in that the photosensitive element (5) is arranged in a macro converter (2).