cameras and films (hs v1)

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Cameras and Film The basic camera The modern camera has all the basic parts of a pinhole camera, except that a lens replaces the pinhole. A simple lens is a disc of glass that has been shaped and polished. It will bend a set of parallel light rays so that they meet (focus) at a point (the focal point). 90 Parallel Light Rays Convex surface Focal Point Focal length Optical axis The light rays travelling to the lens from a distant object are almost parallel, and an upside down (and left-right inverted) image of the object is produced on the focal plane. The distance between the focal plane and centre of the lens is called the focal length. Compound lenses A compound lens is made up of several lenses of different shapes, sizes and thicknesses. These cancel out each other’s imperfections (aberrations) to form a much sharper image. Nearly all modern lenses are compound lenses and they also have a coating of magnesium flouride to cut down unwanted reflections, or flare.

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Page 1: Cameras and films (hs v1)

Cameras and FilmThe basic camera

The modern camera has all the basic parts of a pinhole camera, except that a lens replaces the pinhole. A simple lens is a disc of glass that has been shaped and polished. It will bend a set of parallel light rays so that they meet (focus) at a point (the focal point).

90Parallel Light Rays

Convex surface Focal PointFocal length

Optical axis

The light rays travelling to the lens from a distant object are almost parallel, and an upside down (and left-right inverted) image of the object is produced on the focal plane. The distance between the focal plane and centre of the lens is called the focal length.

Compound lenses

A compound lens is made up of several lenses of different shapes, sizes and thicknesses. These cancel out each other’s imperfections (aberrations) to form a much sharper image. Nearly all modern lenses are compound lenses and they also have a coating of magnesium flouride to cut down unwanted reflections, or flare.

Page 2: Cameras and films (hs v1)

Basic parts of a modern camera

The camera body is a light tight box.The shutter stops light reaching film except when taking a picture. When the shutter button release is pressed fully down, the shutter opens to allow light to pass through the lens to the film. The lens focuses light on to film to form an image. It can be manipulated to adjust the focus. The lens opening is also known as the aperture or f stop. The size/diameter can be changed by moving a set of circular blades called the iris diaphragm. This also changes the strength of light falling on the film. The film transport moves the film and holds it flat on the focal plane. The emulsion faces the lens.

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400 ASA/ISO

FilmFilm is photo-sensitive. It is made up of tiny silver crystals that vary in size. The bigger the crystal, the more sensitive it is to light, therefore less light is required for an image to be captured. The emulsion of black of white film is panchromatic, which means that is sensitive to all colours. In colour film there are three separate emulsions sandwiched together. They are sensitive to blue, green and red light, in turn.

100 ASA/ISO

The higher the ASA number, the faster and more sensitive to light

is the film

FILM A FILM B FILM C

Small grains give fine detail

Slow film

Used in very good light

Good for copying and billboards

Medium Grains

Medium film

Used in average light

General purpose

Large grains give coarse detail

Fast film

Used in poor light

Good for action photographs

SLOW SPEED FILM

25 – 200 ASA

Longer exposures are required to pick up as much information as possible. Needs a tripod or flash in low light situations.

FAST SPEED FILM

400- 1800 ASA

Can be used at night time without a flash or tripod. Very grainy. When printed large the grain is very obvious. Used by sports photographers, journalists etc.

Page 5: Cameras and films (hs v1)

ApertureThe size of the lens opening, the aperture or the f-stop, controls the amount of light that passes through the lens.

The lens shown ranges from f/2.8 to f/22. Each setting is one stop from the next and each lets in twice as much light as the next smaller opening, half as much light as the next largest.

The greater the f-stop number, the smaller the lens opening and the less light that is let in.

Which one lets in the most light?

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Aperture

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At slow shutter speeds, like 1/30 any movement blurs the image.

At medium speeds, like1/125, there is still some blur, but there is generally sharper focus.

Fast shutter speeds, like 1/500 will freeze all movement and make the point of focus sharp.

Slow speeds:

4s

2s

1s 1/2

1/4 1/8

1/15 1/30

Medium speeds:

1/60

1/125

Fast speeds:

1/250

1/500

1/1000

1/2000

Shutter Speed

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Depth of field

Depth of field refers to the amount of space (foreground, middle-ground and background) that is in or out of focus within an image. It is the distance between the nearest and farthest objects that appear in focus in a picture.

Depth of field can be used creatively to isolate a subject and make it stand out against its background. This is a useful technique for portraits. It is possible to blur unsightly or unwanted backgrounds, or add mood to an image by including a blurred foreground. All of this can be achieved by using a large aperture (e.g. 2.8) which gives a shallow depth of field. This technique is called selective focusing.

It is also possible to have a greater depth of field, with the foreground, background and subject all in sharp focus. This is achieved with a small aperture.

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Shallow or great?

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Shallow or great?