Focus factor (Focal Lenth Multiplier)

Many digital SLR sensors than 35mm film area is small, a typical digital SLR CCD sensor length ratio of slash 35mm film small 1.5 times. Typical 600 million pixel digital SLR sensor size (43.3/28.1, slash length than 35mm film small 1.54 times) as a result, small than 35mm film sensor only photographs of the central part of the film, resulting in "vision missing

Many digital SLR sensors than 35mm film area is small, a typical digital SLR CCD sensor length ratio of slash 35mm film small 1.5 times.

Typical 600 million pixel digital SLR sensor size (43.3/28.1, slash length than 35mm film small 1.54 times)

Therefore, smaller than 35mm film sensor only photographs of the central part of the film, causing the loss of the "vision."

A 35 film camera need a sticks of focal length larger lens to achieve the vision of the digital SLR sensors. 35mm film slash length and the ratio of the length of the sensor slash is the focal length multiplier (FLM). Let's take two examples of FLM: example 1: digital single lens reflex camera with 35mm film uses the same focal length lens film camera lens imaging sensor 200mm focal length coefficient FLM 1.5, obtained just 35mm camera to the camera and lens 200mm central part, led to the "vision loss", which is equivalent to 35mm camera 300mm lens out of an image (200 x 1.5 = 300mm). The absolute size of the moon does not change, because the focus is still 200mm

Example 2: digital SLR film cameras use than 35mm focal lengths shorter lens film camera lens imaging sensor 200mm focal length coefficient FLM 1.5, due to the use of focal length shorter lens (133mm, 200mm/1.5), digital SLR camera is obtained to 35mm 200mm lens cameras to get the full scope of the image, which is equivalent to 35mm camera 300mm lens out of an image (200 x 1.5 = 300mm). The absolute size of the Moon, because of the shorter focal length lens. (Magnification)

This means that if you put a mm lens mounted on the digital SLR (FLM 1.5 times), it produces a range of perspectives in fact equivalent to 35mm film camera 28mm lens.

However, the shortcomings of the wide angle end sometimes conversion growth Coke side edge. For example, put a mm lens installation in digital SLR, it vision range equivalent to 35mm film camera 300mm lens-300 mm lenses are often more expensive than 200mm. It is precisely because this focal length doubling effects, digital SLR easily to a shorter focal length, the greater the depth of field.

Specialized lenses for digital SLR

Most digital SLR will be able to use the traditional 35 mm camera.

Nevertheless, these programs would have to 35mm film cameras manufactured than the film area small sensor, the lens is too big and too heavy. Digital SLR dedicated lens (Canon short black lens, Nikon DX-series cameras, Olympus 4/3 system lens) than traditional 35mm SLR lens light, because their lens ring size as long as they meet the needs of the sensor.

On a small digital camera

In order to adapt to the small sensors, creating a good 35 mm equivalent vision range, small digital camera lens is usually shorter.

Typical small digital camera sensor length ratio of slash 35mm film 4 times smaller. Small digital cameras marked "7mm" focal length lens, equivalent to x 4 i.e. 28mm 7mm. With the digital SLR, the camera lens ring size as long as they meet the sensor coverage on it, so they shot a compact and cost less. As a small digital camera lens focal length is short, so it's better than digital SLR and in the same 35mm camera vision range, greater depth of field.