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Media College (Chương 2 : Ánh Sáng)(2) PDF Print E-mail
Written by tuyenphuc   
Friday, 26 March 2010 10:10

Phần 2: Thiết bị ánh sáng. Lighting Equipment

Some common types of equipment used in video and photography lighting.

18% Gray Card

A gray-coloured card which reflects 18% of the light which falls upon it. Used as a reference to calibrate light meters and set exposure.

15 gray-card-220

An 18 Percent Gray Card is a simple gray-coloured card which uniformly reflects 18% of the light which falls upon it. Gray cards can be used as a reference to set the camera exposure or to calibrate a light meter (light meters are used to determine which exposure setting is required to produce a medium gray tone).

Gray cards are usually made from coated cardboard or polystyrene and come with a protective cover. They are an inexpensive and useful addition to the photographers' kit.

How to Use a Gray Card

To set your exposure with a gray card, first make sure the camera is in manual mode or is able to hold its settings when you half-depress the shutter button.

Position the card immediately in front of the subject, ensuring that the lighting on the card is exactly the same as the lighting on the subject. If you are using a light meter, take your reading now. Otherwise, half-depress the camera shutter button to save the exposure setting until you fully depress the button (and take the picture).

(Note: This process is very similar to performing a white balance).

Tips

  • At the start of your roll of film, take one photo of a gray card. This acts as a colour correction reference for the film processor.
  • Do not use any old gray piece of cardboard for a gray card. You really need a professionally-made one.
  • When you first purchase a gray card, run a series of tests to establish exactly how it performs in both bright outside light and lower artificial light. Use slide film rather than print, as slide film does not correct exposure errors.

Ballast

A device used to control the electrical current in a light.

A ballast is an electrical device used to control the current in an electrical circuit. A lighting ballast controls the start-up and regulation of fluorescent and high intensity discharge (HID) lamps.

A ballast is necessary for fluorescent and HID lamps because they have a negative resistance, which means if they are connected to a constant voltage source they will continue to draw more current until something melts down. The ballast controls the current and keeps everything working correctly.

Ballasts come in many varieties and complexities, from a simple resisters to computer-controlled units.

Consoles

Hardware and software systems which control lighting. Operated by the lighting technician, consoles coordinate lighting displays on stages, studios, etc.

 15 console01

Lighting consoles are systems which control lighting - much as a sound mixer controls audio and a vision switcher controls video. Consoles are typically a combination of hardware and software.

Operated by a lighting technician, consoles are used in a wide range of applications including stage, studio, film set, etc.

Modern consoles include options for automating certain tasks and effects. Complex productions rely heavily on such automation.

16 console02

Light Meter

A tool used to measure light and indicate the ideal exposure setting. Also known as an exposure meter.

17 lightmeter-extech

A light meter, also known as an exposure meter, is a tool used to measure light levels. Light meters are commonly used in photography, motion film and video to help determine the ideal exposure setting.

Many cameras have built-in light meters and this function is often carried out automatically. However serious professionals still regularly take manual readings.

Reflector Board

A specially-designed reflective surface used to act as a secondary light source. The board is lightweight and flexible, and is normally folded up for transport in a small carry-case.

18 reflector-board01

Sometimes referred to as a "flecky board", this is a specially-designed reflective surface which is usually used to act as a secondary light source. It is particularly useful as a fill light when working in strong sunlight.

Reflector boards come in white, silver or gold surfaces. Many reflectors have a different type of surface on each side, giving you two lighting options. Gold surfaces provide a warmer look than silver or white.

If you don't have a reflector board you can improvise. Almost any suitably-sized object with a reflective surface will do. Some examples include:

  • Windscreen sunshades for automobiles
  • Polystyrene sheets
  • Tin foil on cardboard (try both sides of the foil for different effects)
  • Whiteboard

How to Fold Up a Reflector Board

Reflector boards are lightweight and flexible, and are normally folded up for transport in a small carry-case. They can be tricky to fold up — if you've never done it you may want to read the instructions below and practice in private before having to do it in front of the whole crew!

 19 reflector-fold

Hold the board with your left hand facing forward and your right facing backward. Move your left hand forward and down, while moving your right hand backwards and up.

Keep moving your hands in a smooth motion.

The board will end up folded in a compact circle. You can then return the board to its case.

Gels

Materials which are placed in front of a light source to alter it's characteristics, e.g. colour temperature or dispersion .

Diffusion Gels & Materials

In the context of lighting, diffusion means to spread the light beam out and make it more random.

When you have a single source of light like the sun, the resulting light is very directional and will create shadows where the light does not fall. On an overcast day, water particles in the clouds diffuse the sunlight and make it appear to be coming from the whole sky (reducing shadows in the process).

Video lights tend to create directional light. In some cases this is desirable but sometimes this type of light can be too harsh. In particular, you don't usually want strong shadows on a person's face.

One way to mitigate this problem is to use some sort of diffuser. This usually comes in the form of a gel, filter or piece of material which is placed in front of the light. Professional light fixtures have special holders or clips on the barn doors to attach gels and filters. Wooden clothes pegs can also be used.

20 diffusion-04

More elaborate setups might use large sections of diffusion material mounted in a frame, or in a "softbox" like those pictured left.

You can also bounce light of walls, ceilings and materials (e.g. foamcore) to create different diffusion effects.

Warning: Always be very careful when mounting any gel or material near a light. Lights can get very hot — avoid flammable material and never attach plastic pegs to a light fixture.

22 diffusion-03

Spectrometer

A professional-level instrument which measures the spectrum of light. Technically speaking, a spectrometer analyses the electromagnetic spectrum and measures the intensity of radiation as a function of wavelength.

Stands & Clamps

Systems used to support lights and hold them in the correct position.

In the context of lighting equipment, the term Lighting Support refers to the range of systems used to support lights and hold them in the correct position. This usually means light stands and clamps. Clamps and other accessories are sometimes referred to as grip gear.

23 soft-lightLike microphone stands, most lighting stands and clamps use a standard system of fittings.

On simple light stands like the ones pictured, the light slides down onto the fitting and screws tight.

Clamps like those below can be attached to any appropriate solid object.

 24 lightstand01

25 clamp01 26 clamp02 27 clamp03

 

 

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