Canon SD790 - PowerShot IS Digital ELPH Camera Uživatelský manuál stáhnout pdf (Strana 3)

2.1 Camera hardware 3

2 Cameras and Operating

Systems

Before turning to the virtues of the CHDK, let’s first have a look at some of

the platforms the CHDK runs on. As its name suggests, the CHDK runs on

Canon cameras. Specifically, the classic form of the CHDK runs on Canon

compact cameras, such as Powershot and Digital Elph (Digital IXUS). For the

still-experimental (at time of writing) EOS-CHDK, please see section 9.1.

2.1 Camera hardware

Practically all digital Canon compact cameras (and all of the newer camera

models) are equipped with a zoom lens, allowing for an optical zoom range

from 1:3 to 1:20+. The optical zoom can be extended via an optional digital

zoom. All zoom lenses are equipped with a macro function, which again

can be extended with a digital macro. Digital zoom and digital macro come

at a cost, however: they reduce image resolution because only a part of the

sensor is used for the final image.

Most Canon cameras are equipped with an optical image stabilizer;

usually, these cameras carry the suffix “IS” in their name. “Optical” means

that a lens element is moved to counteract camera shake. With this tech-

nique, it is possible to increase exposure times by a factor of 2–16

(1–4 f-stops) when shooting without a tripod. An image stabilizer is a very

useful feature, especially for telephoto shots and for shooting in low light

conditions.

Most Canon cameras use CCD (charge coupled device) type sensors;

only a few use CMOS type sensors. Smaller models have sensors with a

diameter of 1/2.5 inch (10 mm), while larger models have sensors with a

diameter of 1/1.7 inch (14.9 mm). The focal length conversion factors are

6.2 and 4.6 respectively, compared to the 35mm format.

For most Canon cameras, the resulting image is delivered in the form of

a JPEG file with selectable resolutions and formats, and selectable com-

pression ratios. Top-range cameras offer an option to deliver the RAW sen-

sor data, too. Actually, the prime motivation behind the development of

the CHDK was to enable smaller, low-cost cameras to deliver sensor data in

RAW format. It should be mentioned that digital zoom and digital macro

do not work with RAW format; the format delivers the pure sensor data

without any post-processing.

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Canon SD790 - PowerShot IS Digital ELPH Camera Uživatelský manuál Strana 3