what is aparture? which good if the digital camera has f2.8 compare to f8?

Answer 1

I think you mean aperture.

In photography it's the opening of the lens which limits the amount of light which will be allowed through to create the image.

The larger the number the more light will be required to get the correct exposure with the same ISO.

With an aperture of f2.8 you should be able to use the camera with less light than f8. But you may also be able to change the working ISO to offset this. However, the higher the ISO the more "noise" you may notice in the image.

Depth of field will be more shallow with the lower number aperture. This means with the lens set to f2.8 less may be in sharp focus than if the image was captured at f8.

This can be used creatively to draw attention to the subject.

Answer 2

Aperture, aka f-stop, is a measurement of the size of the opening in the diaphragm in the lens. It is an inverse relationship, which means that the smaller the f-stop number (f1.2, f1.4, f1.8, f2, f2.8, depending on the lens being used) the LARGER the opening in the diaphragm. The larger the f-stop number the SMALLER the opening in the diaphragm.

Depending on the lens being used, think of it this way:

At f1.4, all the light available is being admitted; at f2, 1/2 as much light is admitted as at f1.4; at f2.8, 1/2 as much light is admitted as at f2; at f4, 1/2 as much light is admitted as at f2.8.

Here is a graphical way of looking at it. Lets assign a value of 10,000 to the light we have available.

f1.4 = 10,000
f2 = 5,000
f2.8 = 2,500
f4 = 1,250
f5.6 = 625
f8 = 312.5
f11 = 156.25
f16 =78.125

There is yet another variable that depends on the size of the f-stop and that is the shutter speed. The more light that is admitted the shorter the shutter speed.

f1.4 @ 1/2000 second
f2 @ 1/1000 second
f2.8 @ 1/500 second
f4 @ 1/250 second
f5.6 @ 1/125 second
f8 @ 1/60 second
f11 @ 1/30 second
f16 @ 1/15 second

The less light we admit the longer it has to be allowed to expose our light-sensitive surface, whether film or digital sensor.

Answer 3

On a good Digital SLR, set the dial on "A" (Aperture priority), dial the aperture up and down with the lens cap off and watch the shutter speed go up while the Aperture number goes lower. Watch the shutter speed go down as the Aperture number is greater.

If you are taking pics of a fast moving object, this option is priceless.

Your camera might choose 1/500 sec at f8 in the "P" setting, but on the "A "setting you might be able to get 1/1000 sec at f5.6

If you were at a NASCAR race, you would want that 1/1000sec shutter.

The Rat

Answer 4

The ability to go to f2.8 is preferable. It is a larger opening and considered "faster".

Answer 5

This would explain it better than I can.
http://www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm