Semi Space - text

Semi-space

Appendix
The basic idea of the „Semi-space” is projecting a picture of the half of the space onto the surface of a hemisphere. To realise this I constructed a special camera the operation of which is based on some simple geometric principles.

Geometric principles
1 Between certain points of the Semi-space and the surface of the hemisphere an unambiguous correspondence can be created. Straight lines drawn through the centre of the sphere to given points of the space designate the image of the points of the space on the surface of the hemisphere.
2 The hemispheres can be described as the connection of two circular movements. Starting from the North Pole downwards along a longitudinal circle, while performing a rotary motion around the North-South axis, advancing on the surface of the sphere spirally, we reach the Equator. How many times we rotate around the axis while we perform a 90-degree turn along the longitudinal circle, depends on the relative speed of the two circular motions. I have prepared the camera by joining the above two principles. The sensitised hemisphere stands still while the housing of the camera rotates around it along the vertical axis. In the centre of the hemisphere there is an optic lens which, on the one hand rotates along with the housing and, due to a transmission, in 90 degrees turns around a horizontal axis, on the other. The ratio of the two speeds is 40:1, that is, while the machine turns around the vertical axis ten times, the lens makes quarter of a revolution. These two circular motions create a spiral described in point #2.

The optical system
consists of a lens and a diaphragm.
The right positioning of the lens is of a decisive importance, it should be exactly in the centre of the hemisphere. The mechanism holding the lens allows it to be moved in various directions in order to find the point revolved around which we obtain the sharpest picture. Effacement can thus be minimised. The optic angle is strongly limited, it is 9 degrees. This also plays a role in decreasing effacement, as, according to observation this is the least in the case of the picture drawn by the centre of the lens. It also enhances the feeling of sharpness that the surface of the hemisphere – and thereby the picture – is very big. (The surface of the hemisphere 34 cm in diameter is more than 1800 cm2, as opposed to the 36 cm2 of a 6 by 6 film.) It is also important that we do not want to produce further pictures (enlargements) this being the end product. Thus the border of fuzziness appears in a different way as in the case of photography designed for enlarging, and the picture gives a sensation of sharpness.
The lens is joined to a bellows extension to the other end of which an oblong masque is attached. During exposure the masque should adhere closely to the surface of the hemisphere. This can be fixed with the bellows extension. If there is a leak between the masque and the surface of the hemisphere, the incoming light exposes not only in the field defined by the masque but gets dispersed on the surface of the hemisphere, thus it will be exposed to light. As during photography the masque is in constant motion compared to the hemisphere standing still, exposition will be a stripe. The vertical size of the masque gives the width of the stripe and its size should be chosen so that the spiral stripe should exactly adjust to itself after one revolution. This provides a unified picture on the hemisphere.

Exposition
Exposition is co-ordinated by moving the camera with an electric motor. It follows from the geometry of the spiral that the revolving speed, i.e. exposition, must constantly be changed. As the spiral stripe runs an ever greater course, its peripheral speed continuously increases at a constant revolving speed. This means that the masque advances at an ever greater speed on the surface of the hemisphere, thus the incoming light decreases which results in the uneven exposure of the surface. To avoid this, the construction must continuously be slowed down. As this is not a linear retarding, a table helps to define the speed appropriate for the number of revolutions. The low voltage electromotor can be regulated by a potentiometer, the point of comparison of the speeds is given by the fictitious speed of a bicycle speedometer.
The black-and-white emulsion used is of a low sensitivity, it does not reach that of photographic papers, rendering exposition time rather long. This, naturally, is also influenced by the intensity of the surrounding light. The shortest exposure was one hour and a half by intense sunlight. During exposure the change in the intensity of light must constantly be followed with attention using a photometer and if needed the speed of the camera or the diaphragm must be changed.
The exposed picture I immediately develop into a positive one.

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		Semi-space Appendix The basic idea of the „Semi-space” is projecting a picture of the half of the space onto the surface of a hemisphere. To realise this I constructed a special camera the operation of which is based on some simple geometric principles. Geometric principles 1 Between certain points of the Semi-space and the surface of the hemisphere an unambiguous correspondence can be created. Straight lines drawn through the centre of the sphere to given points of the space designate the image of the points of the space on the surface of the hemisphere. 2 The hemispheres can be described as the connection of two circular movements. Starting from the North Pole downwards along a longitudinal circle, while performing a rotary motion around the North-South axis, advancing on the surface of the sphere spirally, we reach the Equator. How many times we rotate around the axis while we perform a 90-degree turn along the longitudinal circle, depends on the relative speed of the two circular motions. I have prepared the camera by joining the above two principles. The sensitised hemisphere stands still while the housing of the camera rotates around it along the vertical axis. In the centre of the hemisphere there is an optic lens which, on the one hand rotates along with the housing and, due to a transmission, in 90 degrees turns around a horizontal axis, on the other. The ratio of the two speeds is 40:1, that is, while the machine turns around the vertical axis ten times, the lens makes quarter of a revolution. These two circular motions create a spiral described in point #2. The optical system consists of a lens and a diaphragm. The right positioning of the lens is of a decisive importance, it should be exactly in the centre of the hemisphere. The mechanism holding the lens allows it to be moved in various directions in order to find the point revolved around which we obtain the sharpest picture. Effacement can thus be minimised. The optic angle is strongly limited, it is 9 degrees. This also plays a role in decreasing effacement, as, according to observation this is the least in the case of the picture drawn by the centre of the lens. It also enhances the feeling of sharpness that the surface of the hemisphere – and thereby the picture – is very big. (The surface of the hemisphere 34 cm in diameter is more than 1800 cm2, as opposed to the 36 cm2 of a 6 by 6 film.) It is also important that we do not want to produce further pictures (enlargements) this being the end product. Thus the border of fuzziness appears in a different way as in the case of photography designed for enlarging, and the picture gives a sensation of sharpness. The lens is joined to a bellows extension to the other end of which an oblong masque is attached. During exposure the masque should adhere closely to the surface of the hemisphere. This can be fixed with the bellows extension. If there is a leak between the masque and the surface of the hemisphere, the incoming light exposes not only in the field defined by the masque but gets dispersed on the surface of the hemisphere, thus it will be exposed to light. As during photography the masque is in constant motion compared to the hemisphere standing still, exposition will be a stripe. The vertical size of the masque gives the width of the stripe and its size should be chosen so that the spiral stripe should exactly adjust to itself after one revolution. This provides a unified picture on the hemisphere. Exposition Exposition is co-ordinated by moving the camera with an electric motor. It follows from the geometry of the spiral that the revolving speed, i.e. exposition, must constantly be changed. As the spiral stripe runs an ever greater course, its peripheral speed continuously increases at a constant revolving speed. This means that the masque advances at an ever greater speed on the surface of the hemisphere, thus the incoming light decreases which results in the uneven exposure of the surface. To avoid this, the construction must continuously be slowed down. As this is not a linear retarding, a table helps to define the speed appropriate for the number of revolutions. The low voltage electromotor can be regulated by a potentiometer, the point of comparison of the speeds is given by the fictitious speed of a bicycle speedometer. The black-and-white emulsion used is of a low sensitivity, it does not reach that of photographic papers, rendering exposition time rather long. This, naturally, is also influenced by the intensity of the surrounding light. The shortest exposure was one hour and a half by intense sunlight. During exposure the change in the intensity of light must constantly be followed with attention using a photometer and if needed the speed of the camera or the diaphragm must be changed. The exposed picture I immediately develop into a positive one. << top of the page