Digital Images

Aperture: The camera’s aperture is the hole through which light enters the camera. Apertures are measured using a relative scale, called “F numbers” such as F/4, F/5.6, F/8, F/11, etc. The smaller F-numbers refer to larger openings to let in light. The larger the aperture (smaller F number) the less time the camera needs to take a picture. For any particular light level and ISO, there is a range of “equivalent exposures” which will produce the same digitally exposed photograph.

For example, the following combinations of how long the shutter is open (shutter speed) and aperture opening (f number) will produce the same exposure:
  • 1/500 at F/4
  • 1/250 at F/5.6
  • 1/125 at F/11
  • 1/60 at F/16
Although the above settings will produce the same exposure, the results will often look rather different. As an example, if you are photographing a moving car, 1/500 at F/4 will probably give a fairly sharp result because the aperture is only open a very short time.
However, if you use the slower shutter speed of 1/60 at F/16 you will get a blurred result, since the car has moved quite a distance in 1/60th of a second.

Part of the challenge involved with digital photography training is that there are so many different digital cameras available. Since each camera uses different modes, controls, and technologies, digital photography training has to stay somewhat generic.

Many simpler cameras do not allow you to control the aperture independently. However, they may offer different “program modes,” such as a “sports” or “action” program.

These programs use a very fast shutter speed, typically between 1/500 and 1/2000. Check your manual for specific details.

Aspect ratio: the width divided by the height of an image.

Byte: a unit of measure equal to 8 bits of digital information.

Dots per inch (DPI): a measurement of the resolution of a digital photograph. The higher the number the greater the resolution.

Dots per inch (dpi): a measure of the number of pixels per inch.

Histogram: a graph that shows the range of tones from dark to light in a photograph.

Image pixels: the image itself is composed of pixels in a series of rows and columns. The size of each pixel depends on the size the image is displayed. A smaller image size will have larger pixels and a larger image size will have smaller pixels. 
JPEG: the most prevalent standard for compressing image data.

Megapixel: a measurement equal to one million pixels.

Pixel: the single point of a digital image that makes up a photograph. Digital photographs contain thousands or millions of pixels.

RAW image format: the digital information coming directly off the camera sensor with no in-camera processing.

Thumbnail: A small version of a photograph.

Vishaal Bhat

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