I am buying either Sigma 18-200 DC or Tamron !8-200 Di XR. Both 3,5-6,3 Which one is better zoom lense? Can anyone send links with pictures taken with both these lenses?

f1.4 is twice as fast as f1.8. how about 2.8 and the "next level" which is 3.5? is 2.8 twice as fast as 3.5 as well? and 3.5 and 4, 4 and 6.3....so on?

Full F stops are F2 F2.8 F4 F5.6 F8 F11 F16 F22 F32 each time you increase the F number you half the amount of light. F number between those listed are usually half stops so change the amount of light by a quarter.

f/6.3 is only a 1/3 stop from f/5.6... :idea:

On some cameras (default to 1/2-stop), the f/6.3 will be rounded down and register as f/5.6 in the viewfinder and EXIF - unless one programs the camera to increment in 1/3 stop! ;)