[arvydas]

If, for example, f4.0 shutter speed is 1/30, f2.8 will be 1/60 (in that particular environment). You can read about exposure on this site at "Technique" section, [url="http://www.cambridgeincolour.com/tutorials/camera-exposure.htm"]here[/url]or [url="http://www.dpreview.com/learn/?/Glossary/Exposure/Exposure_01.htm"]here.[/url]



A.