WHITE BALANCE

It would be ideal to change the white balance of the camera when there is a change in the colour temperature of the light illuminating a potential shot. There are some cameras that will compensate for colour temperature variation but carrying out a white balance set-up before filming is always a good idea. Sometimes it will be needed to carry out the specified white balance procedure even though the camera switch may be marked “auto white balance” to ensure it is automatically compensated. To successfully white balance a simple routine will need to be followed:

1. Selecting the correct filter for the colour temperature of the light being used. (e.g. tungsten 3200K)
2. Selecting white balance position A or B; it will memorize the setting that will be achieved by the white balance. On either filter position, the two memories can be either A or B but if preset is selected, no setting will be memorized. This is the standard default setting.
3. Filling out the frame with a white matte card that is lit by the same lighting as the intended shot.

The card should not move during the white balance and it should not have any reflections or shading. The card needs to be correctly exposed, you will need to avoid any colour cast from any surrounding light sources and have the white balance the main source of shot illumination. During the white balance process, you may see a progress report appearing in the viewfinder, which will include a number that will indicate the colour temperature that has been assessed. You may need to check the position of the white card and other requirements of white balance if you may find the number higher or lower than the anticipated estimate of the colour temperature. It may indicate the camera is either not lined up correctly or it may be malfunctioning. Whilst the white balance is under way, the auto-iris circuit will adjust exposure to make the output of the green signal correct, then the red and blue channels will be adjusted to equal the green output. The white balance procedure will therefore be dependent on by the fidelity of colour reproduction since the white will influence all other colour combinations.

BLACK BALANCE There are a lot of cameras that may not require a manual black balance meaning that the adjustment will have to be carried out automatically whenever required. The black has no colourcast since the black balance will set the black levels of the red, green and blue channels. This will only normally be only required if: · The camera has not been used in a while · The camera has been moved between different air temperatures · The air temperature has altered · When the gain selector values have been changed If a manual black balance must be done, you must do 2 things: 1. White balance to equalize the gains and then black balance 2. White balance again.

LIGHT OUTPUT
The tungsten light source: The heat effect from the electric current that flows through the tungsten filament which is how light is produced. The visible spectrum from these sources is continuous and produces a smooth transition of light that is outputted between the adjacent wavelengths. The intensity of the outputted light will be varied if the current is changed (dimming) which affects the colour temperature also although this is usually kept within acceptable limits. Light from a discharged light source is produced as a by-product of an electrical discharge through a gas. The particular mixture of gas present in the glass envelope effect the colour of the light, the colour of the light also depends on the phosphor coating of the fluorescent tube. HMI’s; which are discharged light sources designed for film and television lighting, are not as stable as tungsten but do have a greater efficacy, they are compact and they produce light that approximates the daylight.

PULSED LIGHT SOURCES
Fluorescent tubes; for home, office, factory and neon signs, does not produce a constant light output but it does give short pulses of light depending on the mains supply. The light output of a usual daylight-type fluorescent tube for the normal eyesight give of a bluish green cast to a tungsten balanced camera but does not register high intensity blue and green spikes.

The improvement of Phosphors has made the fluorescent tube/cold light acceptable for television and film came after recent years of development. They are able to provide tungsten matching and daylight matching colour temperature. More or less steady light output are a result of high frequency operation; i.e. >40 kHz.

COLOUR RENDITION INDEX (Ra)
The colour rendition index or Ra can be used to indicate the suitability for use in television production (Ra of 70 is regarded as the lower limit of acceptability for colour television). The use of a scale of 0 – 100 is used as a method of comparing colour fidelity and consistency of a light source.

www.candyjarfilms.co.uk

THE ZOOM LENS

The zoom lens is a complex and sophisticated component of any video camera. lts performance may be described in brochures in impenetrable techno-speak that many, at first glance, may feel has little or nothing to do with the ‘real’ business of filming. To take this view is a mistake, as above all else, the lens characteristics are the most important visual influence on the appearance and impact of an image.

Altering the settings on focal length, lens angle, zoom ratio, aperture or depth of field will have a significant influence on the perspective and the depiction of space and composition when setting up a shot. It is a fallacy to believe that the camera will truthfully record whatever is in shot whenever you put your eye to the viewfinder and press to record. If you are unaware of how the choice of focal length, etc., will affect the chosen image then this important creative decision will be left to chance and accident.

Prime lens or zoom?

Before the introduction of colour television, video cameras usually had four, individually turret-mounted prime lenses (a lens with a fixed focal length) on the front of the camera. By rotating the turret, the correct lens for a specific focal length would be chosen for a shot. Selecting a prime lens to match the needs of a shot is still common film practice. For technical reasons, such as faster working methods and the option to zoom on shot to capture close-ups without adjusting the camera, meant the wide majority of colour video cameras were fitted with a zoom lens. With the ability to change the lens angle quickly and easily, it can be easy to forget what focal length is being used which could compromise the space or perspective of the shot so be wary.

Image size

With CCD (charged couple devices) coming in different sizes (2/3 inch, 1/2 inch, etc.), the variation in flange-back distance the mechanical connection between lens and camera, and the variation in cable connections with the camera, it is often impossible to interchange lenses between different makes or models of cameras. The image formed by the lens on the face of the CCDs is called the image size of the lens. This must match the size of the camera sensor. Lenses designed for different sized formats (pick-up sensor dimension) may not be interchangeable. The image size produced by the lens may be much smaller than the pick-up sensor and probably the back focus (flange _‘back) will not have sufficient adjustment. A common lens on a broadcast video camera is a 14 x 8.5 f1.7 zoom with a minimum object distance of 0.8 m or below.

www.candyjarfilms.co.uk