Clearing my doubts with AF points

[Exhaust]

Hi guys, i have been reading a couple of articles and videos on how to get tack sharp images. And the information i gather shows that if i were to use Auto-area AF, and while doing a group shot , 9 AF points lights up.. it does not mean that all these 9 points will be focused on, because the camera can only focus on any 1 point at a time. It simply means that the camera has managed to 'guess' that out of these 9 points, one of them will be the intended focal point.

So if i want to great a nice tack sharp group photo. I would simply use single point AF, with a smaller aperture (f8-f11), make sure my shutter speed is at least 1/125 (1/100-1/125 seems ok), iso100. that would do the trick too right? even though it is a single-point af, it doesn't mean that the person which i focused on, will be the sole person who is sharp in the picture. The sharpness would depend on the aperture sized used, focal length of my lens and the distance between me and the group.

Right?

 

[gohjialong]

I think it would be wrong to say that the camera is able to focus at one point, am i right? cos as long as the distance of the subject is aligned to the focal point, it will be in focus right?

 

[spitfire93]

subjects lying on the focal plane will all be in focus

so if the group happens to all lie on the plane, there is a chance that multiple af points will light up (lighting up really means that point is focused on, instead of showing which af points the camera is guessing from)

 

[GRbenji]

The camera focus on a plane parallel to the sensor. The AF point made use of the subject to determine that plane. Any thing on this plane will be very sharp. How sharp are those off the plane will depend on the DOF which is affected by the aperture.

 

[spitfire93]

aperture (f8-f11), make sure my shutter speed is at least 1/125 (1/100-1/125 seems ok), iso100.

try not to treat it like something u have to die die follow. be more flexible and adapt!

 

[Octarine]

So if i want to great a nice tack sharp group photo. I would simply use single point AF, with a smaller aperture (f8-f11), make sure my shutter speed is at least 1/125 (1/100-1/125 seems ok), iso100. that would do the trick too right?

There is no magic formula. If you use f/8 then the ambient light or the usage of flash / studio lights will tell you whether you can use ISO 100. Same for the shutter speed: your focal length should be the first indicator (rule of thumb: shutter speed faster or equal to 1/focal length), followed by the questions whether you want to include or exclude motion blur, maybe combined with 2nd curtain flash ..? Many options, many camera possible camera settings.