Digital Camera Buying Guide - More Basics

These are features of intermediate level to high end cameras that allow to control things like shutter speed, aperture, ISO equivalent and white-balance. All digital cameras have at least one automatic mode which lets the camera guess the best settings when taking a picture. Most medium or larger cameras have at least some manual controls.

Aperture

Aperture refers to how much light a camera can let in at a given shutter speed. A larger aperture, denoted by small numbers such as F2.8, lets more light in then a small aperture, denoted by larger numbers such as F8. Aperture also affects the distances that appear to be in focus when a picture is taken. This is called depth of field (DOF).

Cameras with larger maximum apertures work better in low light and have an advantage when it comes to image quality. They are also more expensive because they require larger lenses. On an ILC, the maximum aperture is defined by the particular lens, so it is not specified for the camera.

Shutter-Speed

Shutter-speed is the duration for which a camera records light to take a single picture. Shutter-speeds allowed by a camera is described as a range measured in seconds and fractions of a second. For example, a range of 1/1000 to 4 lets it can take pictures from as fast as 1/1000th of a second down to 4 seconds.

Action Photography: Shutter speeds of 1/1500 or more.	Fast shutter speeds give a camera the ability to clearly capture objects in motion and take good pictures in very bright light. Cameras that can shoot faster than 1/1500s are marked with the Sports Photography icon.
Night Photography: Reaches shutter-speeds longer than 4 seconds.	Slow shutter speeds give a camera the ability to capture detailed pictures in low light. Camera which reach shutter-speeds below 4s are marked with ther Night Photography icon.

Films for traditional cameras come in different sensitivities to light which is simply refered to as ISOInternational Stantdards Organization, organism that defined how film sensitivities are measured.. The term ISO has been reused for digital camera and refers to an equivalent sensitivity. A higher ISO rating means more sensitivity to light but produces pictures with more noise which is similar to pattern of film grain.

Hover above the labels below to see what different ISO sensitivities can look like on a small-sensor camera. Keep in mind that equal ISO sensitivities are not equivalent between cameras. Particularly with large-sensor cameras which have an inherant advantage and tend to show less noise than cameras with smaller sensors.

Modern digital cameras often reach at least ISO 3200 and some as high as 204,800. The problem is that not all sensitivities are usuable despite being available. In general, ISO performance is proportional to sensor-size. That being said, cameras generally do a good job a few stops below their maximum full-resolution sensitivity.

To see what a top-of-the-line full-frame DSLR circa 2012 can do in terms of sensitivity and image noise, check out the ISO sample page from the Canon EOS 5D Mark III review.

The focal length is a measurement determined by a camera's lens. When measured in 35 mm film equivalent, it serves to determine the angle of view of  pictures taken. The smallest the equivalent focal length, the wider the angle of view and vice-versa.

Optical zoom is just the ratio between the longest and the shortest focal length. For example, a lens that is 35-105mm has a 3X optical zoom, so does a 50-150mm lens. The difference is that the 35-105mm equivalent lens sees wider, the 50-150mm sees further. Depending on the subject, focal length may actually be more important than optical zoom. Photographers of architecture typically prefer lenses with shorter focal lengths.

Focal Length Multiplier

When a lens is mounted on a DSLR, it shows a different angle of view than it would on a 35 mm film camera. The focal length multiplier, sometimes called crop factor, is the ratio between the focal length of the lens and the focal length of a lens which would give the same field of view on a 35 mm film camera. The focal length multiplier is used to determine the angle of view of a lens on a DSLRFor example, a focal length multiplier of 1.5 makes a 28 mm lens have the same field of view as a 42 mm lens on a 35 mm film camera..

Digital cameras normally focus automatically before a picture is taken. This is called Autofocus. All cameras can autofocus but they do need a compatible lens in the case of interchangeable lens cameras. Some specialty lenses cannot autofocus at all.

Some digital cameras also support Manual Focus mode to manually control the focus distance. MF is useful in situations when the camera cannot properly focus automaticallyTypically when the subject is too dark, low contrast or reflective.. It is also useful to take pictures fasterNo need to wait for the camera to focus before snapping the picture. when a subject is known to appear at a certain distance.

Instead of manual focus, some cameras have an Infinity Focus mode which sets the focus distance to infinity. Others have a Pan Focus mode which sets the focus so that everything beyond that point is acceptably sharpThis is called the hyperfocal distance..

All digital cameras can store their images in the JPEG format. The JPEG format is designed to keep file sizes manageable. When used at the highest resolution and highest quality settingAlso know as the lowest compression ratio., resulting images are of excellent quality.

For advanced needs, some cameras can store images in a file-format called TIFF. This is a much larger format which preserves very slightly more information.

Advanved digital cameras may also record RAW data intead of an image. This RAW data is then converted by a computer into an image using specialized software. This can help create images with a different look than what the camera can produce.