Photography Step By Step » Camera System

Burst (Continuous)

Andrei — Tue, 07 Sep 2010 06:00:34 +0000

This mode represents the digital camera’s ability to take several shots immediately one after another, similar to a film SLR camera with a motorwind. The number of frames per second and total number of frames differs greatly between camera types and models. The fps is a function of the shutter release and image processing systems of the camera. The number of frames that can be taken is defined by the size of the buffer where images are stored before they are processed (in case of a before image processing buffer) and written to the storage card.

The number of frames per second and total number of frames that can be shot in burst mode is continuously improving and is higher as you move from consumer digital compacts to professional digital SLRs. Digital compacts typically allow 1 to 3 fps with bursts of up to about 10 images while digital SLRs have fps of up to 7 or more and can shoot dozens of frames in JPEG and RAW. Some even allow an initial burst of higher fps followed by a slower but continuous fps until the storage card is full.

Buffer

Andrei — Fri, 03 Sep 2010 06:00:26 +0000

After the sensor in the camera is exposed, the image data will be processed and then written to the storage card. The buffer inside a digital camera consists of RAM memory which holds the image information before it is written out to storage card. This process makes the time between shots shorter and allows burst (continuous) shooting mode. The very first digital cameras didn’t have any buffer, so after you took the shot you had to wait for the image to be written to the storage card before you could take the next shot. Now most digital cameras have relatively large buffers which allow them to operate as quickly as a film camera while writing data to the storage card in the background (without interrupting your ability to shoot).
The number of images that can be shot in continuous (burst) mode is affected by the location of the buffer within the camera (which normally is not specified by the producer). The buffer memory is located either before or after the image processing.
Before Image Processing Buffer
In this method no image processing is carried out and the RAW data from the CCD is placed immediately in the buffer. In parallel to other camera tasks, the RAW images are processed and written to the storage card. In cameras with this type of buffer, the number of frames which can be taken in burst mode cannot be increased by reducing image file size. But the number of frames per second (fps) is independent of the image processing speed (until the buffer is full).
After Image Processing Buffer
With this method the images are processed and turned into their final output format before they are placed in the buffer. As a consequence, the number of shots which can be taken in a burst can be increased by reducing image file size (e.g. shoot in JPEG, reduce JPEG quality, reduce resolution).
Smart Buffering
The “smart buffering” combines elements from the above two buffering methods. Just like in the “Before Image Processing Buffer” the unprocessed image data are stored into the buffer allowing for a higher fps. They are then processed and converted into JPEG, TIFF or RAW. But instead of writing the processed images to the storage card they are stored in the buffer. Therefore, the image processing is not bottlenecked by the writing to the storage card, which happens in parallel. Moreover, it constantly frees up buffer space for new images since processed images takes up less space than RAW once, especially in the case of JPEG. Just like in the “After Image Processing Buffer”, the output images are then written from the buffer to the storage card. But an important difference is that here the image processing happens in parallel with writing to the storage card. So the image processing of new images can continue while the other images are being written to the storage card. This means that you do not necessarily have to wait for the entire burst of frames to be written to the CF card before there is enough space to take another full burst.

Batteries

Andrei — Mon, 30 Aug 2010 19:57:18 +0000

Disposable AAs
Given the high power consumption of digital cameras, it is economically and environmentally unjustified to use disposable batteries other than in emergency situations when your rechargeables are depleted. Disposable Lithium AAs are more expensive than Alkalines, but having about three times the power packed in half the weight, they are ideal to carry with you as a backup.
Rechargeable AAs (NiCd and NiMH)
NiMH (Nickel Metal Hydride) rechargeable AA batteries are much better than the older NiCd (Nickel Cadmium) AAs. They have no “memory effect” (explained below) and are more than twice as powerful. Capacities are constantly improving and differ per brand.
Rechargeable Lithium-ion Batteries
Li-ion (Lithium-ion) rechargeable batteries are lighter, more compact, but more expensive than NiMH batteries. They have no memory effect and always come in proprietary formats (there are no rechargeable Li-ion AAs). Some cameras also accept disposable Lithium batteries, such as 2CR5s or CR2s via an adapter, ideal for backup purposes.
Charging
Fully charged batteries will gradually lose their charge, even when not used. So if you have not used your camera for a few weeks, make sure you bring a freshly charged battery along on your shootout. Charging NiCD batteries before they are fully discharged will reduce the maximum capacity of subsequent charges. As the effect gets stronger when repeated often, it is called “memory effect”. It is therefore recommended to recharge the batteries only after they are fully depleted. To a lesser extent, this is also useful for NiMH or Lithium-ion batteries, although they have virtually no memory effect. Doing so will also increase the life span of the battery which is determined by the number of “charge-discharge” cycles that depends on the type and brand.

Autofocus

Andrei — Mon, 15 Feb 2010 15:51:45 +0000

This feature can be found in all digital cameras. In autofocus (AF) mode the camera will automatically focus on the subject in the focus area in the center of the LCD or viewfinder. Many digital cameras allows the user to also select other autofocus regions that will be indicated on the LCD/viewfinder.

In “single AF” mode, the camera will focus when the shutter release button is pressed halfway. Some cameras offer “continuous AF” mode whereby the camera focuses continuously until you press the shutter release button halfway. This shortens the lag time, but reduces battery life. Normally a focus confirmation light will stop blinking once the subject in focus. Autofocus is usually based on detecting contrast and therefore works best on contrasty subjects and less well in low light conditions, in which case the use of an AF assist lamp is very useful. Some cameras also feature manual focus.

AF Servo

Andrei — Sat, 13 Feb 2010 07:39:07 +0000

This system allows the camera to maintain focus on subjects that are moving. It is a very useful feature for sports or wildlife photography and it is normally found on digital DSLRs.

Autofocus Servo is normally triggered by switching focus to “AI Servo” on Canon, or “Continuous” on Nikon, followed by half pressing the shutter release. The camera will continue to focus on the subject as long as the shutter release will be half pressed or fully depressed (actually taking shots). The Autofocus Servo usually also puts the camera into “release priority” mode so that the camera will take the shot when the shutter release is depressed, regardless of the current AF status.

AF Assist Lamp

Andrei — Sun, 24 Jan 2010 15:29:33 +0000

This is a lamp which is used to illuminate the subject you are focusing on when shooting in low light conditions. The lamp is usually located beside or above the lens barrel. These lamps are not very powerful and they usually only work over a short range, up to about 4 meters. The light that they make is usually visible light, but there are lamps which uses infrared light instead. This is better for candid shots where you don’t want to startle the subject. Notable higher end external flash systems feature their own focus assist lamps with far greater range.

The picture above is a hologram AF found on some Sony cameras. This works by projecting a crossed laser pattern onto the subject. This bright laser pattern helps the camera’s contrast detect AF system to lock on to the subject. The system works well as long as the subject is large enough to be covered by several laser lines.

AD Converter

Andrei — Sun, 17 Jan 2010 19:19:40 +0000

Sensors from your digital camera consists of millions of pixels with photodiodes which convert the energy from the light (actually from the incoming phototns) into an electrical charge. That electrical charge is then converted to a voltage which is amplified to a higher level so that it can be further processed by the ADC (Analog to Digital Converter). In accordance with the voltage value, the ADC classifies it into a number of discrete levels of brightness and assigns each level a binary label (a number in binary code, consisting of 0 and 1). The ADCs are classified by the number bits that this labels are formed of. So a one bit ADC will classify the voltage as either 0 (black) or 1 (white). A two bit ADC would categorize it into four (2^2) groups (black-00; white-11; and two levels in between-01 and 10). Most consumer digital cameras use 8 bit ADCs, allowing up to 256 (2^8) distinct values for the brightness of a single pixel.

The minimum resolution (bit rate) of an ADC is determined by the dynamic range (accuracy) of the sensor. For example if the dynamic range of the sensor is 1000:1 (or 60dB) the ADC must be at least 10 bits which is 2^10 = 1024 discrete levels. This will avoid loss of information. Theoretically a 10 bit ADC is the perfect fit for this dynamic range (1000:1), a 12 or 14 bit ADC will not generate additional tonal information other than noise. However, in practice it makes sense to overspecify the ADC to 12 bits to allow for some margin of error on the ADC. It is also useful to have extra bits available to minimize posterization or banding when applying the tonal curve to the linear data.
Often, marketing material advertises the bit rate of the ADC to suggest the digital camera or scanner is able to output images with a high dynamic and tonal range. From the above it is easy to understand that this is only true if the sensor itself has sufficient dynamic range. The tonal range and dynamic range can never be larger than the dynamic range of the sensor.
Digital SLR cameras have sensors with a higher dynamic range and are usually equipped with 10 or 12 bit ADCs. Normally such cameras offer the option to save the 10 or 12 bits of data per pixel in RAW because JPEG only allows 8 bits of data per channel.