Unit 30: Camera and Lighting Techniques for Moving Image Production

Geometrical (Quantum) Optics

  • A simple view of this study leads us to use a model of the behaviour of light as being one of imaginary rays
  • These rays represent light as following simple geometric representations
  • Using geometry it is possible to map the phenomena that is occurring when for instance these rays interact upon objects

Quantum Optics

  • This is a study of light with respect to what is happening at a sub atomic level
  • It is at a level we might understand what is actually happening when light interacts with the natural world around us
  • It tells us what happens to the energy implicitly linked to light
  • Our most natural form of light is that of the sun whose rays travel some 93 million miles to light our world
  • These rays also warm our world, another feature of light

Producing light (Sound design)

  • When we consider light at a sub atomic level we see its basic element is the photon
  • It is these that we see emanating from our light sources or being reflected from objects
  • Electrons that surround atoms are put into an excited state or have their energy levels raised
  • When they then return to their normal state this difference in energy levels create a photon
  • The speed at which the energy levels

Reflectance

  • Law of reflectance states that the angle of reflectance is equal to the angle of incidence
  • The ray will be reflected off the surface at the same angle as it hits it
  • We can see reflectance on any glossy surface although to a lesser extent than that of a mirror

Light on surfaces

  • Light reflecting from a mirrored or glossy surface is known as a specular reflection
  • Rough surfaces reflect rays at various angles, known as diffused reflection
  • We will use these types of surfaces to reflect light when filming

Mirrors

  • Rays follow the law of reflectance into the mirror

Curved mirrors

  • Light rays will tend to bend on reflection and so tend to be closer together
  • The continuation of the rays behind the mirror will tend to converge (Come together)
  • They will converge deeper into the mirror than the object. This will make then make the object appear larger
  • The rays reflected off the mirror whilst closer together nevertheless are still diverging
  • Image will be formed in front of the mirror. This image termed as a ‘real image’ as opposed to the reflected image termed a ‘virtual image’ will be upside down

Light – The Inverse Square Law

  • Light from a lantern or any other point source will tend to diverge with distance
  • The intensity of light observed from a source of constant intrinsic luminosity (i.e. a lantern) falls off as the square of the distance from the object.
  • This is known as the inverse square law for light intensity
  • Thus, of I double the distance to a light source the observed intensity is decreased to (1/2) squared = ¼ of its original value
  • To put it more simply is to consider it in terms of light intensity at certain distances
  • A simplified way of calculating the new value is to think of it as a fraction of the original value.
  • The formula 1/d2 will effectively give us the fraction compared to the original intensity
  • If you calculate it using the simplified formula:

New intensity = 1/d2

We can see at 2ft the intensity is ½ squared or ¼ of the original intensity, which was 64 lux

A quarter of 64 then would be 16 lux

Light – Photometry (Frequency and Colour of light)

  • Goes from infrared to ultraviolet
  • Red at lower frequencies
  • Violet at higher frequencies
  • Photometry can be described as the measurement of apparent brightness of light
  • These measurements are usually weighted to take account of the human eye. Like the ear, the eye is more receptive to certain frequencies.
  • This will manifest as certain colours being apparently brighter than others even though the power or energy is the same.
  • If you consider the lamps you have in the home they are normally rated in electrical power 40 watts, 60 watts and 100 watts.
  • This generally indicates the apparent brightness of them, but how would you rate the brightness of the sun?
  • This type of measurement is only useful if the light is generated from electrical sources and only certain sources at that (Tungsten type lamps)
  • We have seen the advent of low energy lamps, these are supposed to give off the same light at much lower powers.
  • All the radiated power emitted by a light source and perceived by the eye is called luminous flux. The unit of measurement is the lumen
  • A light source emits its luminous flux in different directions and at different intensities
  • The visible radiant intensity in a particular direction is called luminous intensity. The unit of measurement is the candela
  • Illuminance indicates the degree to which an area is illuminated
  • It is the ratio between luminous flux and the area to be illuminated. The unit of measurement is the lux
  • The luminance of a light source or an illuminated area is a measure of how much the eye is stimulated and therefore of how great an impression of brightness is created in the brain.
  • The luminous intensity of this area divided by its size apparent to our eyes is its luminance. It is measure by candelas per square metre (cd/m2)

Microphones

  • Characteristics – Microphones are different and are used for different applications
  • Sensitivity – how it reacts to levels of sounds
  • Directivity – how it responds to sounds in free space
  • Handling noise – how it reacts to handling

Optics: The Lens

  • Refraction is the bending of light rays through a medium
  • Refrection in lens inverts image at the focal plane
  • Transmission – How light is let through a medium
  • Repriocity refers to the reciprocal nature of how features of the lens are interrelated this is: Aperture, focal length and shutter speed. All of these will affect depth of field i.e. to maintain the same DOF opening. 1 stop on aperture can be compensated by 1 step shutter speed
  • ISO, ASA Values – film stock. These are termed film speed. The faster the film, the quicker the image is formed, the GRAINIER the image

Smear (CCD) – CCD are prone to smear areas of high exposure

Skew

Wobble – Elongation of objects when tilting the camera

CMOS – Digital from picture elements – better than conversion of CCD

On the whole, CCD is better for high end work. CMOS is cheaper and less ‘smeary’, but has rolling shutter problems. Extra circuitry to make good CCD is expensive

Quantum efficiency – How much light is converted to signal

Foveon – Works more like film – Layers are exposed according to the frequency of light. Far more at colour reproduction than CCD or CMOS. Much more costly than the other two.

Shutters – Non rolling shutter expose whole sensor. Rolling shutter expose small area

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