Process and device for photographing microscopic objects
The invention relates to a process for selective photography with shortened and stored exposure time values or with exposure time values corrected during the exposure process, a measurement spot of variable spatial location as well as exposure field markings being made visible before and after the exposure, as well as to a device for carrying out this process. 
     German Patent Specification No. 2,619,853 discloses a microphotographic device as an attachment camera for microscopes, which permits an exposure correction during the exposure process by means of a fixedly built-in 50/50 neutral beam splitter. In this case, it is disadvantageous that the beam splitter fixedly disposed in the photographic beam path consumes 50% of the available quantity of light for the exposure control. As a result of this, only 50% of the light passes to the film. As a consequence of this, the exposure times are lengthened by the factor &#34;two&#34;. This circumstance has a very disadvantageous effect, especially when--as is customary with special microscopy processes--objects of very low light intensity are to be observed and recorded. 
     It is therefore the object of the present invention to overcome the disadvantages of known microphotographic devices and processes and to provide a process as well as a device, with which process or with which device a great gain in time can be achieved, especially when large-format camera attachments are employed, and moreover there is an expansion of the photographic recording possibilities, especially of miniature fluorescence exposures with reduced exposure times, which are otherwise no longer possible, in consequence of object destruction with the formerly customary long times. A further partial object consists in furthermore obtaining the advantage of the exposure correction during the exposure for a series of practical cases of application with fluorescence exposures by the selection of the exposure program, i.e. in combining both photography with shortened exposure times and also the selective exposure correction during the exposure. 
     With a process of the initially mentioned type, this object is achieved, according to the invention, by the features of claim 1, as well as in each instance alternatively by claims 2, 3 or 4. Further refinements are evident from the process claims 5 to 8. The object is furthermore achieved by a device for carrying out the initially mentioned processes according to claim 9; further refinements are evident from the device claims 10 to 14. 
    
    
     An embodiment of the invention is diagrammatically represented in the drawing. 
    
    
     The photographic beam path 16 proceeds from an object 6 to be examined and extends along the optical microscope axis 26 via a photographic eyepiece 19, a beam splitter system 1 and a shutter 20 to the image exposure plane 18, in which, for example, a film can be positioned. 
     The observation beam path 13 likewise proceeds from the object 6 and is deflected at a splitter surface of a splitter prism disposed in the optical microscope axis 26 into the microscope eyepiece 5, where it passes to the observer 27. A dark flap 12 can, in the working position, keep extraneous light on the observer side away, in the case of specified program functions. 
     An illumination partial beam path 14 proceeds from a lamp 8, which illumination partial beam path, after passing through a format reticule 3, which moreover exhibits a sharpness cross, and after deflection at an appropriate optical component, onto a 50/50 beam splitter 25, where it it recombined with a further illumination partial beam path 15. The illumination partial beam path 15 likewise proceeds from the lamp 8 and, after two-fold deflection, impinges on a full mirror, which is disposed in the measurement beam path 10 so as to be slidable out and which can be designed also as a rotary mirror 11, and falls from there through a stationary integral measurement diaphragm 23 as well as a detail measurement diaphgram carrier 7, which is disposed immediately therebehind so as to be slidable out and which is held within its plane so as to be spatially variable, onto the already mentioned beam splitter 25, from which the combined illumination beam path 14 15 impinges on the beam splitter system 1. In the case represented, the glass cube 1a is situated in the working position, i.e. in the optical microscope axis 26. This glass cube 1a possesses a fullmirror-coated diagonal surface, which stands in a 45° position in relation to the vertical optical microscope axis 26 and to the combined illumination beam path 14, 15. 
     The beam splitter cube 1c disposed beside the glass cube 1a exhibits a beam splitter surface in the diagonal position, which exhibits a discrete transmission/reflection ratio between 95/5 and 99.5/0.5--preferably 99/1. 
     The beam splitter cube 1b exhibits a splitter surface in the diagonal position, which exhibits a transmission/reflection ratio of 50/50. It should be emphasized that use can be made, in addition or alternatively to the indicated beam splitter tubes, also of those which exhibit other physical or geometric beam splitting properties. The adjustment of the beam splitter system 1 takes place by motor. 
     The measurement beam path 10 proceeds from the beam splitter system 1, more precisely from the glass cube 1a situated in the working position in the drawing, and is thrown, after deflection at the beam splitter 25 when the full mirror (or rotary mirror 11) is swung out, onto the light receiver 21. The rotary mirror 11, which is shown as a flap mirror which can be moved out in the graphical representation, is moved by motor under program control and possesses a labyrinth, which, in the working position, closes off the light receiver 21 in a light-tight manner. This brings advantages for the dark-current compensation. Thus, for example with known microphotographic devices, it is only possible to achieve a dark-current compensation if use is made of a photographic tube which contains a slider setting in which no light can pass to the light-measuring device. 
     The dark flap 9 which is pivotable into the beam path 15 by motor under program control has two functions. In the case of integral measurement, the dark flap 9 is switched into the working position for the observation of the image, in order to prevent the integral measurement diaphgram 23 from being illuminated from behind. Otherwise, this would be superposed, in its entire magnitude, on the object image. The second function consists in that it remains switched on in the case of each light measurement. By this means, scattered light from the ventilation system of the lamp house is prevented from being superposed on the measurement light and falsifying the measurement. 
     The change between integral measurement and detail measurement takes place in the device according to the invention or the corresponding processes in such a manner that the integral measurement diaphragm 13 always remains fixed in its position. For a spot measurement, the spatially variable partial measurement diaphgram 24 or its carrier 7 is switched, for example by means of a lifting magnet, closely in front of the integral measurement diaphragm 23 by key pressure from the control unit 28. A gray filter (1%), which was formerly customary with a known microphotographic process and which adapted the transmission of the integral measurement diaphragm to the transmission of the detail measurement diaphragm, can be dispensed with in the case of the present invention, since, in place of this, a beam splitter cube 1c can be run into the working position. The detail measurement diaphragm carrier 7 is mounted, for example, by a lifting magnet on a carriage, which is operated by means of two electric motors from the control unit 28. 
     The markings for exposure fields on the format reticule 3 can be applied on a movable mask, which is adapted to a spherical-shell surface, which corresponds to the curvature of the image field. By this means, the image sharpness of the markings remains preserved over the entire field. 
     If required, a color temperature measurement beam path 17 can be constructed. The color temperature measurement is introduced by pushing the deflecting mirror 29 into the measurement beam path 10. The mirror 29 situated in the working position is registered, for example, by a reflex light barrier, which on its part switches over the control unit 28 to color temperature measurement. The measured color temperature appears in the display of the control unit 28, in place of the otherwise displayed film speed. 
     The control unit 28 is shown purely diagrammatically in the figure with the associated exposure control system 2 and the release key 22. The arrows illustrate the functional links to the individual opto-mechanical components. 
     In place of a color temperature measurement attachment, a computer flash sensor with a housing can also be fitted by means of the deflecting mirror 29. The position of the mirror 29 is recorded, again, by a reflex light barrier. An appropriate opto-electronic coupling leads, in the control unit 28, to an automatic flash readiness; in this case, when this function is operative switching takes place automatically to integral measurement. 
     The high transmission/reflection ratio of, for example, 99/1 of the splitter surface of the beam splitter cube 1c is achieved by the difference in refractive index between glass and cement layer of the pertinent component. The beam splitter system 1 is moved by motor under program control, and is positioned by fork light barriers, which are not shown.