QUOTE(ieR @ Jan 10 2010, 03:08 PM)
A550 does not have F2.8 sensor. even if it does have a F2.8, it helps with accuracy, not speed. coz without it, it will still goes hunting under low light thus longer AFlock, so in the end, i dont think F3.5 lens would hunt more then F2.8 iether. but u wont have the problem with flash attached.
do u have any idea how the image is transfered until the AF sensor?
even i use F22, my OVF is still bright, and when i use F2.8 it does not go brighter, so basically, inside the shutterbox, the amount of light stay more or less the same. and knowing that they have to pass through the mirror glass (semi translucent) onto a mirror to reflect it down to another mirror, then only to the AF sensor, and no, it wont brighten up the area anyway.
Don u notice that when your SONY AF lens attached to the camera body, it's at the wide open aperture (yes the widest). Until the moment you press the shutter. then the Aperture contract to the desired aperture and snap.. So that why when u use F22, there is no effect on your viewfinder, unless u press the DOF preview button. Goto to shop, grap a A700 and above and try out the DOF button n you will see

If u have a manual lens then u try to focus at F22, sure ur camera cry.
How to AF when everything have a very same contrast?edit: I should say how to AF at F22, when the scene is dark and the DOF is very deep...
But then that's not the issue, when the subject is in focus, then it's considered Focus.
This post has been edited by hkhk: Jan 10 2010, 05:16 PM