SYNCHRONIZED  LIGHT  CONTROLLING  SCREEN  AND  SHUTTER  CAMERA

by J.C.M. van den Berg


This concerns the against-the-light camera, which can cope with information of high contrast.

The reason for developing it was the until recently existing limitation, that one could not take photographs into or against full sunlight - thus with the full sun in the picture, - because this led to practically complete overexposure of the intended information.
This was the challenge: to go against this well known conception, in spite of all that, and to find a method which would allow photographing against full sun light or against other light sources or to fiercely lighter areas, so that afterwards - depending on the findings - other properties and other applications possibly could be discerned.

When you first look at other well-known practical applications of camera systems, it appears that - with the most current systems - projection of the picture on sensitive material is done via two sorts of shutter systems, namely:
Firstly the in-between-the lenses-shutter.
Secondly the focal-plane-shutter.

Here is a short summary of the differences between the two types.
Regarding position:

        *  The in-between-the lenses-shutter is found in the object-lens or beneath in the near vicinity of it.
       
        *  The focal-plane-shutter is located just in front of the photosensitive recording material.

Regarding the function:

       *  The in-between-the-lenses-shutter allows, for a split second, the whole image projection to fall on the photosensitive material.

       *  The focal-plane-shutter in the same way lets a longer existing image projection fall successively strip-wise on the photosensitive recording material.

Both systems have their advantages and disadvantages, in an optical sense as well as from a technical construction point of view.

What is striking here, is the fact that objectives "with an open eye" - as it were - "look at" the space around the object.

When the sunlight falls in a slanting direction a sun-hood is then quickly put to use.

It is therefore clear that the sun as a light source in the object space, which is the space out of which the information must be obtained - can have prolonged access to the object-lenses. This makes coping with the information as a result of overexposure and/or internal reflections in the optical system rather problematic.


What then is the principle of the against-the-sun-camera?

Well, in this camera a new type of shutter system is applied, with which the object- or image space is scanned. Thus, by this means, the object space is successively, hence in portions, allowed to reach the lens or lenses of the camera. Furthermore, during this scanning the photosensitive material is protected as far as possible against information disturbances by means of a screen - situated just in front of the photosensitive recording material - in which a slit-shaped opening is found.
The shutter system - so called integrated shutter - consists therefore of two parts working together.

One part - the slitter screen system of a particular construction - is placed in front of the object-glass, and carries out the actual scanning of the object space, and the second part is placed behind the object-glass, namely just in front of the photosensitive material, and screens the recorded information and the information yet to be recorded from interference, which results from reflections in the whole system.
This letter part, although the second part as an element in the constructions is more or less similar to the known focal-plane-shutter, is in its function however, completely different.

The system in front of the lens(es) consists of a number of slit lathes which are set up such, that  'parallel'  beams of light are formed, which are afterwards built up into a strip image by the lens system. These slit lathes were chosen instead of parallel partitions - so named high blinds - and this was caused simply by the unacceptably large number of reflections which would occur with the use of partitions, no matter how well they were also fitted with low reflection or light absorbent material. Because of the choosing of lathes, which then have to be as thin as possible against the edges of the slit, these reflecting surfaces were avoided. However, this is at the cost of somewhat more than half of the effective lens surface area, which is comparable to well over a diaphragm stop. This is not such an objection with today's optical technique, as rather high light intensity objectives are in vogue.

The scanning takes place by moving the lathes relatively to each other or by moving the whole lathe system as one fixed whole. The lens may or may not move with it. This last point is again a possible application for panoramic photography.

The function of the against-the sun/light-camera is in general two-fold:

        1. To let in information of low light intensity without interfering influences from irrelevant sources in the object space. This is achieved by means of a slitter screen system which forms a number of parallel beams which are combined through the object-lens to form a strip image of relatively high light intensity.

        2. To let in information of high light intensity without interfering with low light intensity information already recorded or yet to be recorded. This is achieved by means of a co-moving screen - and the slit which is present in it - , which stops excessive stray light from an overexposed object. Also internal reflections are thus during the scanning minimized.

It is clear from the examples and technical drawings shown, that for example a combination of two such cameras working at a relative angle-preferable 90 can produce very much of all the desired information. Certainly when the 'scanning' is of a very narrow nature and besides, the possibilities to adapt the photosensitive material, are used.

Furthermore, this new principle of admitting information to the optical system and the synchronized screening of the photosensitive material can mean substantial greater possibilities for various optical systems.
This is so compared to the generally applied coating of lens surfaces.

Besides that, this principle may be of application in areas which concern areas of different wave-lengths, also areas for other spectra!

With the use of TV-cameras with quick moving shutter systems of this type, it should be possible to obtain information against a background of full sun or more usually into spotlights without problems. Low light intensity information can electronically be raised at will, and possibly computer controlled, while the too high light intensity information can be toned down, if not automatically replaced by a neutral information spot.
Here we can see many areas of applications.

Regarding the notion of  "aberration in colors in the light-spectrum"  I would like to make the following remark.
This is, in my opinion, for the most part to be blamed on internal reflections in the lens system. With the use of the integrated shutter this fault decreases remarkably and even, if so disturbing, with the application of filters it can be much more selective.


1981/1982


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