A camera dolly is a specialized piece of filmmaking and television production equipment designed to create smooth camera movements (cinematic techniques). The camera is mounted to the dolly and the camera operator and focus pulleror camera assistant, usually ride on the dolly to operate the camera. The dolly grip is the dedicated technician trained to operate the dolly.

2. Movement

The camera dolly may be used as a shooting platform on any surface but is often raised onto a track, to create smooth movement on a horizontal axis known as a dolly shot. Additionally, most professional film studio dollies have a hydraulic arm that raises or lowers the camera on the vertical axis. When a dolly grip operates a dolly on perpendicular axes simultaneously, it’s known as a compound move.
Dolly moves may also be executed without track, giving more freedom on the horizontal plane and with it, a higher degree of difficulty. These are called dancefloor moves and may either be done on the existing surface (if smooth enough) or on an overlay designed for dolly movement. The ground overlay usually consists of thick plywood as a bottom layer and masonite on top.
Camera dollies have several steering mechanisms available to the dolly grip. The typical mode is rear-wheel steering, where the front wheels remain fixed, while the wheels closest to the operating handle are used to turn. A second mode, round steering, causes the front wheels to turn in the opposite direction from the rear wheels. This mode allows the dolly to move in smooth circles and is frequently used when the dolly is on curved track. A third mode, called crab steering, where the front wheels turn in the same direction as the rear wheels. This allows the dolly to move in a direction diagonal to the front end of the dolly.

3. Types

Studio dollies are large, stable and can feature hydraulics. These are the first choice for studio, backlot and location shoots when using professional cameras. A studio dolly usually needs a specialized operator called a “dolly grip”. Lightweight dolly systems are simpler, more affordable and are best used with lighter-weight cameras. Lightweight systems are usually favored by independent filmmakers and students because they are easier to operate. There are riding dollys and also dollys that support only the camera, so that the operator needs to walk alongside. Any dolly that is compact in size when set on floor wheels is called a “doorway dolly.” The best way to be able to replicate the same camera movement for multiple takes (which is important for editing) is to use a dolly on track.

4. Track

Dolly tracks used for heavy cameras have traditionally been constructed of steel or aluminium. Steel, although heavier than aluminum, is less expensive and withstands heavier use. Longer track segments, while heavier to transport, allow track to be laid straighter with less effort. Curved track is also available. Plastic versions of track have been used with lightweight dolly systems. In the 2000s, flexible rubber track allowed quicker set up and easier transportation for use with light cameras.

Source: Wikipedia

5. How to build a camera dolly

I have watched a lot of movies in YouTube regarding this subject, but I find this most explanatory. It is easy to create and it is cheap. This type of homemade camera dolly is perfect for amateur filmmakers and for independent film studios.

An aspect ratio specifies the ratio of width to height. Video and still picture frames have a frame aspect ratio, and the pixels that make up the frame have a pixel aspect ratio (sometimes referred to as PAR). You record video for television in either a 4:3 or 16:9 frame aspect ratio. Additionally, different video recording standards use different pixel aspect ratios.

2. Frame aspect ratio

Frame aspect ratio describes the ratio of width to height in the dimensions of an image. For example, DV NTSC has a frame aspect ratio of 4:3. A typical widescreen frame has a frame aspect ratio of 16:9. Many cameras that have a widescreen mode can record using the 16:9 aspect ratio. Many films have been shot using even wider aspect ratios. When you import clips shot in one frame aspect ratio into a project that uses another frame aspect ratio, you decide how to reconcile the different values. For example, two common techniques are used for showing a 16:9 movie on a 4:3 standard television. You can fit the entire width of the 16:9 movie frame within the 4:3 television frame. This placement leaves black bands above and below the movie frame, called letterboxing. Alternatively, you can fill the 4:3 frame vertically with the entire height of the 16:9 frame. Then, you pan the horizontal position of the 16:9 frame within the narrower 4:3 frame so that important action always remains inside the 4:3 frame. This techniques is called pan & scan.

3. Pixel aspect ratio

Pixel aspect ratio describes the ratio of width to height of a single pixel in a frame. Pixel aspect ratios vary because different video systems make various assumptions about the number of pixels required to fill a frame. For example, many computer video standards define a 4:3 aspect ratio frame as 640 pixels wide by 480 pixels high, which results in square pixels. Video standards such as DV NTSC define a 4:3 aspect ratio frame as 720×480 pixels, which results in narrower, rectangular pixels because where more pixels lie within the same frame width. The computer video pixels in this example have a pixel aspect ratio of 1:1 (square). The DV NTSC pixels have a pixel aspect ratio of 0.91 (nonsquare). DV pixels, which are always rectangular, are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video. If you display rectangular pixels on a square-pixel monitor without alteration, images appear distorted; for example, circles distort into ovals. However, when displayed on a broadcast monitor, the images appear correctly proportioned because broadcast monitors use rectangular pixels.

3.1 Common pixel aspect ratios

Source: Adobe Help