difference of ap... f/2.8 and f/4 anyone care to show picture difference.tnks^^

[photogenicly]

anyone care to show the difference between a pic taken with the aperture of 4 and a pic taken with an apeture of 2.8

 

[Headshotzx]

I don't have a pic, but with regards to the technicalities behind that (excluding DOF):
If your shutter speed is 1/30 at f/4, you will get 1/60 at f/2.8 (twice as fast)
or
If your your shutter speed is 1/60 at f/4, ISO800, your shutter will be 1/60 at f/2.8, ISO400.

f/2.8 vs f/4 is basically twice the amount of light.

There's an fstop comparison here on a 200mm f/2.0L IS: http://www.the-digital-picture.com/Reviews/Canon-EF-200mm-f-2-L-IS-USM-Lens-Review.aspx Scroll down

Cheers
Zexun

 

[unseenshadows]

In addition to that, f/2.8 will have a shallower depth of field and rounder out-of-focus highlights, otherwise known as bokeh.