The camera (obscura)
One of the amusements of our forefathers was the camera
obscura . it was a room without any windows.and when the door was closed it
would have been pitch black inside except for the fact that from a tiny hole in
the roof came rays of light which falling upon the whitened surface of a table-top
/reproduced a picture of the outside world immediately surrounding the room..
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| The camera (obscura) |
If we reduce our room to the size of a small box with a tiny
hole at one end. and the flat surface of a plate film at the other we have an
instrument which we call a camera .the principle of every camera that is made,
however elaborate it many otherwise be a
light tight box, a hole at one end and a flat piece of material sensitive to
light at the other end on which the light rays can fall.
In the camera obscura the light was allowed to fall upon the white surface for as long as the spectators wished to observe the image . the outside world is hardly ever still leaves rustle people walk about, see all that movement on the screen .
In the camera if the recorded picture is to be free from blurring and confusion, it is necessary to allow the light to enter for a time, so short that movement will not be apparent in the picture, but in sufficient quantity to be able to cause the necessary surface of the plate or film.
Aperture the useful area the lens through which the light is passing is known as the aperture.two lenses of entirely different focal length photographing in exactly the same conditions will be used at the same aperture .although in fact the actual areas through which light passes will different very greatly in the two lenses. That is because although the large lens is letting though more light, that light has to be spread over a much larger area to form a bigger image, and therefore the intensely of light which actually reaches the film or plate in both cases is the same
In the camera obscura the light was allowed to fall upon the white surface for as long as the spectators wished to observe the image . the outside world is hardly ever still leaves rustle people walk about, see all that movement on the screen .
In the camera if the recorded picture is to be free from blurring and confusion, it is necessary to allow the light to enter for a time, so short that movement will not be apparent in the picture, but in sufficient quantity to be able to cause the necessary surface of the plate or film.
This accomplished by controlling the quantity of light
passing through the hole in the camera at any one moment, and the period of
time during which it passes.
By increasing the size of the hole in the camera the
quantity of light can be made sufficient for any ordinary purposes. It then
becomes necessary to use a lens. Otherwise
the picture would be indistinct. It may so happen ,how ever that under very bright light through.
A mechanism called a “diaphragm “ or “stop” is then used to cut down the size
of the hole. In simple cameras it takes the form of a metal plate pierced with
a hole of the desired hole dimensions, which is placed in front of larger hole
in the camera. In more expensive instrument it is a more elaborate mechanism, known
as an “iris diaphragm” because it operates like the closing at the will of the
photographer .the size of the opening is known as the “aperture”
The time during which the light passes through the hole is controlled by shutter. Which normally closes the hole, and merely uncovers it for the period required by the photographer. This is dealt with in next my post. In some forms of camera the hole remains open all the time. and the shutter works very close to the surface of the film or plate, protecting it from light until the time comes to take photograph.
Source : Teach Your Self Photography by Stanley W. Bowler
The time during which the light passes through the hole is controlled by shutter. Which normally closes the hole, and merely uncovers it for the period required by the photographer. This is dealt with in next my post. In some forms of camera the hole remains open all the time. and the shutter works very close to the surface of the film or plate, protecting it from light until the time comes to take photograph.
Source : Teach Your Self Photography by Stanley W. Bowler
Aperture
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| Aperture |
Aperture the useful area the lens through which the light is passing is known as the aperture.two lenses of entirely different focal length photographing in exactly the same conditions will be used at the same aperture .although in fact the actual areas through which light passes will different very greatly in the two lenses. That is because although the large lens is letting though more light, that light has to be spread over a much larger area to form a bigger image, and therefore the intensely of light which actually reaches the film or plate in both cases is the same
Aperture numbers, more commonly known as “ f ” numbers show the relationship between the diameter of the hole in the lens and the
focal length of the lens.
Source : Teach Your Self Photography by Stanley W. Bowler
Source : Teach Your Self Photography by Stanley W. Bowler
