Digital Photography Terminology

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Digital Photography Terminology

Post by Silvor » Thu Apr 18, 2013 1:01 pm

The aperture is the hole inside the lens that allows light through. Aperture is measured in "f" numbers - a ratio of the diameter of the hole and the focal length of the lens. The size of this hole can be adjusted – a larger hole allows more light in, a smaller hole less. An important effect of this is the depth of field. A smaller hole (higher "f" number) produces a lot of depth of field. The reverse happens with a larger hole (smaller "f" number). In digital photography, DSLRs can produce a range of depth of field effects. Compact digital cameras can't. This is due to the smaller sensors and shorter focal lengths used.

Stands for Complementary Metal Oxide Semiconductor. A type of sensor commonly found in more professional level cameras. See sensor for more information.

Depth of field
Depth of field is a measure of how much of a scene (from the front to the back of the image) will be in focus. Although not strictly digital photography terminology, the affect still applies to digital cameras.

In landscape photography it's common to want everything in focus, from the rocks in the foreground to the hills in the distance ("deep" depth of field). For portrait photography it's usually best to have a shallow depth of field (i.e. keep only part of the image in focus). This allows the subject to be in clear focus, but makes the background blurred.

A piece of opaque plastic that sits over the top of a flashgun. It's job is to soften the light from the flashgun, and therefore reduces harsh shadows caused by a 'bare' flash.

Stands for Digital Single Lens Reflex. This is the digital equivalent of a SLR camera. The difference between this and a traditional SLR is that a DSLR doesn't need film. The photograph is recorded on a digital image sensor and saved onto a memory card.

ISO is a term "borrowed" from film photography. In film photography the ISO was a measure of how sensitive film was to light. It was called film speed. The higher the number, the more sensitive it was (and the film was called "fast film"). E.g. ISO 100 was not that sensitive, ISO 1600 was very sensitive.

In digital photography the number (still called "ISO") refers to how sensitive the image sensor is to light. By making the sensor more sensitive to light, photos can be shot with higher shutter speeds and/or in lower light.

The downside of making the image sensor more sensitive is that it introduces noise into the picture. Noise is the digital equivalent of film grain.

Not strictly digital photography terminology, "macro" means the ability for a camera (or lens) to focus so near to the subject that it is captured life size on the image sensor.

The term macro is used more loosely these days, and usually refers to the ability to get close up shots (not necessarily life size). Typical macro subjects are flowers and insects.

In digital photography terminology, noise is the digital equivalent of film grain. It shows up on digital photographs as small coloured blotches, usually in the darker areas of an image. Noise often goes overlooked in snapshots, but becomes very obvious if enlargements are made.

Noise is worse in digital photos taken in low light. It can be removed to some extent by software, but a better quality digital camera will usually produce less noise in the first place.

Whereas film grain can add atmosphere to a photograph, digital noise is generally considered to be unattractive. Digital photographers looking for a "grainy" effect aim to start with a clean image (i.e. free from digital noise), and then add the grain effect afterwards using software.

Polarizing filter
Polarizing filters attach to the end of a camera lens (usually, but not always, a digital SLR) and are designed to cut out light from a particular direction, for example, reflections from water or glass. The effect is impossible to achieve using software; polarizing filters therefore need to be used when the photo is taken, not applied at the post processing stage.

In digital photography terminology, resolution is a measure of the number of pixels there are on a sensor. The resolution of digital cameras is measured in "megapixels" – millions of pixels. It works by a simple bit of maths – multiply the number of pixels along the bottom of the sensor by those up the side. For example, a sensor with 3000 pixels along the bottom, and 2000 up the side equals 6,000,000 pixels in total. That would make it a 6 megapixel camera.

Theoretically it is possible to change the sensor in a digital camera (say, to upgrade a 5 megapixel sensor to a 10 megapixel sensor). In practice though, so much of the camera would have to be replaced it makes this impossible to do.

The electronic chip that records the image in a digital camera. They come in two main types. CCD (Charge-Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) are the most common. CCDs are used almost exclusively in compact cameras, CMOS sensors are used in larger, and more expensive DSLRs.
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. X3– a new type of sensor developed by Foveon. Used only in Sigma DSLRs and a couple of Polaroid compact cameras.

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.

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.
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