Video Camera Basic Functions

3 main functions

1.Lens

2.Iris

3.Focus

A lens is a transparent object with two refracting surfaces.

The illustration below shows the range of lens types:

One or both surfaces are curved in order to collect light from one direction, change the convergence of the light rays and focus

them onto a surface in the other direction.

Lenses are found in nature (e.g. the eye)

and

in technology (e.g. cameras)

The TV Camera Lens is made up of a series of individual lenses. This arrangement focuses a small sharp image of the scene on to the camera ‘s chip or target plane

Focal length of lens describes its magnifying power

On digital cameras, focal length is often expressed as 35mm film camera equivalent

Higher focal length number indicates a greater image magnification Telephoto ~100-300mm Normal ~50mm (human eye) Wide angle ~18-35mm

Typical point & shoot camera 3x zoom range: 35-105mm (35mm equivalent)

How We See Light – The Eye

Light is gathered through the pupil and focused by the lens onto the retina.

The retina is covered in light sensitive cells called rods and cones.

Tiny electrical pulses are sent down the optical nerve to the brain where they are assembled into an image.

How The Eye Deals Detects Light

95% of the retina is made of rods, sensitive to luminance (brightness/intensity/black or white info) and work at low light levels only.

5% of the retina is made of cones that are sensitive to chrominance (colour) and work in only good light levels.

This is why in darkness we see black and white and edges.

The Eye

There three cones are all sensitive to a different wavelengths of light.

We have cones sensitive to red, green and blue light.We are most sensitive to green, less to red and even

less to blue.We actually see 60% green, 29% red and 11% blueAll video devices work on the same principles as the eye

and because we are least sensitive to colour. This is where the most compression is used. This is explained more further on in this presentation.

Camera Iris

The iris is an adjustable opening which controls the amount of light coming through the lens

The size of the Iris/aperture opening is measured in f-stops

when you open up one stop, you double the light going through the lens; when you stop down one stop, you cut the amount of light going through the lens in half

Auto Iris

Auto Iris controls the amount of light that is used to expose the camera’s image sensor

The camera has a built in light meter that evaluates the total amount of light reflected from the subject. It then averages this light and sets the correct exposure.

FocusTo see the image /Scene clearly is called a proper focus

Professional cameras usually have a manual focus ring at the front of the lens housing. Turn the ring clockwise for closer focus, anti-clockwise for more distant focus. Consumer cameras have different types of focus mechanisms — usually a small dial.

Auto-focus Lenses

Focus Technique

Make sure the camera is set to manual focus.

Zoom in as tight as you can on the subject you wish to focus on.

Adjust the focus ring until the picture is sharp. Turn the ring clockwise for closer focus, anti-clockwise for more distant focus.

Zoom out to the required framing — the picture should stay nice and sharp.

Camera White Balance

White balance adjustment In the light of a particular color temperature, to adjust the white levels of the R, G, and B channels of a color video camera

so that any white object shot in that light is reproduced as a truly white image.

How White Balance Works

All digital cameras have an auto white balance setting that allows the camera to detect the color of the light and balance it correctly.

When you look at a white object, it appears white to you regardless of the light source. When lit by an ordinary household bulb, or a fluorescent light, or outside in daylight it still looks white to your eye.

But to the camera’s eye, each of these light sources is different and each produces a tint of color on the white object. And unless the camera makes some sort of adjustment for this variation in light color, a white object will not appear white in your photos.

In fact, everything in your photo will have a color cast to it… it is just more obvious in the whites and near whites than in other colors. This is the function of the white balance feature in digital cameras.

The image was shot using the camera’s auto white balance setting. The light was daylight and the color is correct for this subject.

Light is measured in degrees Kelvin, such as 3200K or 5800K. This is known as the color temperature of a light source.

The light was daylight, but the setting was for cloudy daylight. Though the color is not correct, it could still be OK, if you wanted a slightly warmer feeling.

For this shot , the setting for tungsten (or indoor light). Since daylight is much bluer than indoor light, the result was an overall blue cast.

Shot Types

EWS (Extreme Wide Shot)The view is so far from the subject that she isn't even visible. This is often used as an establishing shot.

VWS (Very Wide Shot)The subject is visible (barely), but the emphasis is still on placing her in her environment.

WS (Wide Shot)The subject takes up the full frame, or at least as much as possible. The same as a long shot.

MS (Mid Shot)Shows some part of the subject in more detail whilst still giving an impression of the whole

subject.

MCU (Medium Close Up)Half way between a MS and a CU.

CU (Close Up)

A certain feature or part of the subject takes up the whole frame.

ECU (Extreme Close Up)

The ECU shows extreme detail.

Aspect Ratio

The term Aspect Ratio refers to the width of a picture (or screen) in relation to its height. Ratios are expressed in the form

"width x height".

Most Common Aspect Ratio

4x3This is the standard

television format used throughout the second half of the 20th Century. Some times referred to as 12x9.

16x9This format has

gained acceptance as the new standard for widescreen TV, DVD and high-definition video.

21x9 (Cinemascope)A very wide screen format used for theatrical release movies.

Converting Between Aspect Ratios

16:9 4:3

21:921:9