Page 19 - (DK) Advanced Photography Guide

E Q UIPMEN T 17

DYNAMIC RANGE READ/WRITE SPEED

A sensor’s dynamic range is the ratio of the minimum The storage capacity of a memory card is just one aspect
amount of light that is needed to record the details in of its specification. Almost as important is its read/write
shadows to the maximum amount of light possible before speed, which is the rate at which data—photos or video—
details in the highlights are lost due to overexposure. can be recorded to and then read back from the card,
Usually, the larger a sensor’s photodetectors are, the either by your camera or by a PC. The faster that data can
greater their dynamic range, so larger sensors, such as be written to the card, the less likely it is that the camera
those in full-frame cameras, have a greater dynamic buffer memory will fill when you are shooting continuously
range than the sensors in compact cameras. This results or when shooting with Raw+JPEG selected.
in fewer problems, such as image noise or loss of detail in
the shadows or highlights of an image.

PHOTODETECTORS BUFFER MEMORY

Photodetectors are cavities on an image sensor that capture A camera’s buffer memory is a temporary store for image
photons (elements) of light. The number of photons captured data until it can be saved to the memory card (determined
determines the brightness of the image pixel associated with the by the card’s read/write speed). If the buffer memory fills,
photodetector. A photodetector completely filled with photons the camera won’t let you continue shooting until it clears
produces a white, fully exposed pixel; a photodetector that sufficiently. The “burst rate” of a camera is how many images,
receives no photons will produce a black pixel. and of what type, you can shoot before the buffer memory fills.

DIGITAL IMAGE PROCESSOR MEMORY CARD
Once an image is exposed, the analog data captured by the The most commonly used memory card is currently the Secure
sensor is converted to a digital signal and sent to the digital Digital (SD) type, available in different capacities and a variety of
image processor. This decodes the color information from the read/write speeds (see above left). The latest type of SD card at
photodetectors to create the full range of colors of a digital the time of writing is the SDXC, which is available in sizes up to
picture. It also reduces image noise, sharpens the image, and 512GB. Another type of memory card, called the XQD, may
creates a finished JPEG, if required (unless shooting in Raw). offer higher capacities and read/write speeds than the SDXC.

2 3 4 5 6 7 8 9

US_016-017_Understand_sensors.indd 17 05/02/2018 14:34