Understanding Digital Camera : Basic of Digicam

IMAGE SENSOR

At the heart of every digital camera is a light-sensitive silicon chip called a sensor, to gather the image data, whereas a traditional camera exposes light to emulsion film. The sensor takes the place of film for recording images.

SENSOR TYPE

Sensor is the electronic chip that records the image in a digital camera. They come in two main types : 

CCD (Charge-Coupled Device)

CCDs are used almost exclusively in compact cameras. This is a light sensitive chip used in your digital camera for image gathering. The CCD Pixels gather the colour from the light and pass it to the shift register for storage. CCD's are analogue sensors, the digitising occurs when the electrons are passed through the A to D converter. This "Analogue to Digital" converter converts the analogue signal to a digital file or signal.

CCD Sensor in compact digicam

CMOS (Complementary Metal Oxide Semiconductor) 

CMOSs are used in larger, and more expensive DSLRs. These produce lower amounts of power consumption, but are not as popular as the CCD sensors used in most digital SLR's. (To see the detail comparison of CCD vs CMOS click here)

 CMOS sensor in DSLR

There are other types, but not well used, JFET (Junction Field Effect Transistor) – developed by Nikon and used in a very small number of their cameras and X3– a new type of sensor developed by Foveon that used only in Sigma DSLRs and a couple of Polaroid compact cameras. 

SENSOR SIZE

Camera sensors come in a variety of sizes, the smallest are used in compact cameras. Bigger sensor is better.

There are some "size type" of sensor :

• Full frame 35mm (36mm x 24mm sensor size) used on Full Frame DSLR
• APS-H (Advanced Photo System type-H) with 29mm x 19mm sensor size, used by CANON
• APS-C (Advanced Photo System type-C), with +/- 22mm x 15mm sensor size used on most DSLR
• Four Thirds or 4/3 (17mm x 13mm) used on most mirrorless digicam
• Compact sensors : 1/2.5" (5.7mm x 4.3 mm), 1/1.8" (7.2mm x 5.3mm), 2/3" (11mm x 8.8mm) used in compact digicam, phone camera, web cam, etc.

Most digital SLRs use larger sensors than the average compact camera. A good rule of thumb is that the larger the size of the sensor, the bigger each light-collecting pixel can be and the more light it can record without the need to have the signal over amplified. The result of these bigger pixels is a lovely sharp, clean image that doesn't suffer from graininess when setting the camera at higher ISO or sensitivity levels. At top end of the market, digital SLRS have either APS-C (or DX-sized sensors) or full-frame chips, which are the same size as the image area on an old-school piece of 35mm film. These really large sensors have both a high resolution and large pixels, which means they can record high-quality images even at high ISO sensitivities. These sort of images can be reproduced at very large sizes while maintaining really high quality.

SENSOR RESOLUTION or MEGAPIXEL

The quality of any digital image, whether printed or displayed on a screen, depends on its resolution, or the number of pixels used to create the image. Megapixel (MP) relates to the number of pixels per unit length of image. Bigger megapixel is better in cropping work or large printing.

6 MP   : 12 x 18 inci
10 MP : 16 x 24 inci
16 MP : 20 x 30 inci
24 MP : 24 x 36 inci

CAMERA LENS

Apperture Value or f-number
The aperture range of a lens refers to the amount that the lens can open up or close down to let in more or less light, respectively. Apertures are listed in terms of f-numbers, which quantitatively describe relative light-gathering are.

An f-number of X may also be displayed as 1:X (instead of f/X), as shown below for the Canon 70-200 f/2.8 lens (whose box is also shown above and lists f/2.8).

 

Focal Length

The lens' focal length determines the magnification of the image projected onto the image plane. Focal lengths are usually specified in millimetres (mm), but older lenses might be marked in centimetres (cm) or inches.

Types of Lens

Prime Lens

The opposite of a zoom lens, prime lenses have one fixed focal length. They represent the best quality of lens available, but have the big drawback in that they cannot 'zoom in' to a subject.

Prime Lens of Canon DSLR and Pentax-Q 

Pancake Lens

A pancake lens is colloquial term for a flat, thin lens (short barrel), generally a normal or slightly wide prime lens for a camera. 

Pancake Lens and attached on DSLR

Aspherical Lens

A lens with edges flattened so that it is not a perfect sphere. These produce a much superior image.

 Aspherical Lens

Spherical/Conventional vs Aspherical Lens

Wide Angle Lens

The focal length that gives you the widest angle of view. I.e. 10mm, 16mm, 24mm etc.

Canon wide angle lens  (17 - 40mm)

Zoom Lens or Telephoto Lens

A variable focal length lens. The most common on digicams has a 3:1 ratio (i.e. 35-105mm). Detachable zoom lenses include for example, 24-70mm, 70-200mm and 100-400mm

Canon Telephoto Lenses

Macro Lens

These lenses are used for close up photography. The have similar properties to a normal lens, but they are able to focus a lot closer to the subject. Common focal lengths are 50/55mm or 90/100/105mm. The lenses with the longer focal lengths come in very handy for taking close ups of subjects that might otherwise be scared away. The optical quality of a macro lens is normally very high. 

 

 Macro Lens

 

  Fly Macro Lens Photo Shoot*

(*see others macro shoot at www.smashingmagazine.com)

Fisheye Lens

A Fisheye Lens looks surprisingly enough like a fisheye. Their angle of view is a full 180%. There is a trade off in that the pictures produced are distorted in that the centre of the picture almost comes out to meet you whereas the top, bottom and sides of the picture appear to be further away. You can buy both circular and full frame fisheye lenses with full frame being the most common. 

 Macro Lens and Photo Shoot

AUTOFOCUS

All digicams and most modern SLR lenses have this function now. The only difference is that with an SLR you can normally select manual focus if necessary. The lens automatically focuses on the subject as quick as the eye. The lens on the camera focuses automatically when the shutter is half pressed. The viewfinder normally has focussing points shown to assist the user in knowing what will be in focus. 

Focus Assist

Cameras with this send out a light, either normal or infra red to light up the subject to assist with the autofocus in low light or darkness. 

Focus Lock

Focus lock means pre-focussing the subject and re-framing by moving the camera. This is done by half pressing the shutter to focus and fully pressing to expose. Done to ensure crisp, sharp eyes for example.

Multi-Point Focusing

The autofocus systems uses several different portions of the image to determine the correct focus.

Multi Zone Focusing

Many digital cameras now offer multi zone focusing. The camera will automatically determine which zone (centre, left, right, upper or lower) to use to perform the auto focusing. You no longer have to make sure that your subject is in the centre of the viewfinder in order to be correctly focused.

EXPOSURE

Exposure is amount of light that hits the image sensor of film controlled by the shutter speed and aperture.

AE - Auto Exposure
The camera sets the shutter speed and aperture for the correct exposure according to the light. When the camera is set to this mode, it will automatically set all the required modes for the light conditions. I.e. Shutter speed, aperture and white balance. The 3 types are:

1. Program Mode : The camera will choose the shutter speed and aperture automatically, effectively making your SLR a "point-and-shoot". It will normally assign a shutter speed of 60th of a second or higher if possible.
2. Aperture Priority : You choose the aperture setting and the camera will automatically choose the shutter speed according to the lighting conditions. Best setting for controlling the depth of field.
3. Shutter Priority : You choose the shutter speed and the camera will select the correct aperture as long as there is enough light. Good for sports or action photography where you need control over the shutter speeds.

AE Lock

This enables you to lock the current exposure reading and re-frame the shot using the same setting. A half-press of the shutter is normally required to activate this function, fully pressing only when you want to capture the image.

Exposure Bracketing

Camera will take 3 or 5 images and varies the exposure up or down for each photograph ensuring at least one will be well exposed. 

Exposure Compensation

You can lighten or darken the image by under or over exposing the image. (EV compensation).

Over-exposure

This is an image that appears much too bright. The highlights and colours are totally lost and usually unrecoverable even by top software. Either the shutter speed was too long or the aperture was too wide.

SHUTTER

Shutter is the physical device that opens and closes to let light from the scene strike the image sensor. Digicams use both electronic and mechanical shutters. shutter on a camera controls how much light enters the lens and for how long it will enter. This is normally a split-second process and is used to produce special effects in the development of your pictures. Most cameras have ways to adjust the shutter time and how long it stays open.

Shutter Button

 

In photography the shutter-release button (sometimes just shutter release or shutter button) is a button found on many cameras, used to take a picture.[1] When pressed, the shutter of the camera is "released", so that it opens to capture a picture, and then closes, allowing an exposure time as determined by the shutter speed setting (which may be automatic). Some cameras also utilize an electronic shutter, as opposed to a mechanical shutter.

The shutter-release button is one of the most basic features of a handheld camera. Camera phones that lack a physical button for this purpose use a virtual button on the virtual keyboard.

The term "release" comes from old mechanical shutters that were "cocked" or "tensioned" by one lever, and then "released" by another.[2] In modern-day photography, this notion is less meaningful, so is gradually falling from use. 

Shutter Speed

In digital photography terminology, shutter speed is slightly different to traditional photography. Traditionally, the shutter opened when you pressed the camera's button, exposed the film behind the shutter, and then closed again; covering the film back over in the process. With electric sensors the "shutter" is controlled by the camera's computer. A short shutter speed means the sensor is charged for a fraction of a second. For longer shutter speeds, the sensor is kept charged for longer. The shutter noise in most compact digital cameras is created by a small speaker in the camera and mimics a real shutter. It has its use - it lets you know when the photo has been taken. Digital SLRs have no need to mimic a shutter as they work with a combination of shutter and electrically controlled sensor. 

Shutter speed is measured in seconds – or in most cases fractions of seconds. The bigger the denominator the faster the speed (ie 1/1000 is much faster than 1/30).

Shutter Delay

In digital photography terminology, shutter delay refers to the time between pressing the shutter button to the camera actually taking the picture. It is not a term used in traditional photography because the delay was negligible. To overcome the problem of shutter delay most digital cameras allow you to pre-focus by pressing the shutter button halfway, and once the focus has been locked the shutter can be pressed fully. The problem is less apparent with digital SLRs.