what is mean by focal length of a digital camera? what is its significance?

Question

normally we see specs on camara phones and digital cameras.

Answer 1

Here's a good explanation of focal length:
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm

Answer 2

The "focal length" of a lens is the distance between the optical center of the lens and the place where it focuses its image. For conventional cameras, the place where the image is formed is the film plane. For digital cameras, it is the imaging sensor, usually a CCD array.

To make it easier think about this, we can pretend that the rays of light pass through the optical center on their way to the film plane or the imaging sensor. In fact, this is exactly how a pinhole camera works.

Optical zoom works just like a zoom lens on a film camera. The lens changes focal length and magnification as it is zoomed. Image quality stays high throughout the zoom range.

Answer 3

The explanations above wouldn't have helped me much, so I'll have a try myself.
The focal length is a a bit of mathematical wizardry that tells you the field of view for a lens. The focal length is expressed in mm.
With film cameras, any lens with a focal length under 50mm was a wide angle lens. The lower the number, the wider. A 35mm lens was a decent field of view for street photography, 28mm was good for landscapes, and a 15mm lens was almost an outrageous fish-eye lens.
Then, from say 45mm to 55mm, is your normal field of view.
Anything above 55mm is a tele lens. 85mm was perfect for portraits, 200mm was great for zooming in on sports, and with a 400mm lens you needed a tripod to keep things steady.
A zoom lens that went from 28mm to 75mm would cover the vast majority of your shots.
With digital cameras and phone cameras, the mm-ratings on the lens can be all over the place and they usually don't tell you much. Or rather, they mean something different for each model, depending on the size of the sensor. What you want to look for as an indication, is the zoom range as expressed in terms of the '35mm equivalence'. (In this context, 35mm refers to a roll of 35mm film.) The camera might provide those numbers on the lens, too, or you can look up the zoom range in the sales material. You can compare those numbers to the guidelines I just gave.
Sometimes, the camera will just say 5x zoom, but if you look for it, you'll find something like 28-140mm. Those are the numbers you need.

Answer 4

Focal length is the distance from the lens that you want to be in focus.

For example, you might want to take a picture of an object 30 meters away, but have the foreground and background out of focus to highlight the object. The focal length can be varied depending how far the object is, or how much of the foreground and background you want in focus.

It all depends on light, so apperture speed has to be adjusted to get the desired effect.

Answer 5

The focal length of an optical system is a measure of how strongly it focuses or diverges light. A system with a shorter focal length has greater optical power than one with a long focal length

Answer 6

go to google
type focal length
there are many articles to read
you will learn more
than you really wanted to know