Canon 6D Focus Points

[Squidy]

Hi all,

I've got the hang of looking through the viewfinder and selecting a focus point etc. It's pretty awkward looking through while trying to scroll through etc, but that's a story for another day. I've been told you can't select the focus points themselves in live view, however you CAN select where on the screen to focus?

So, I've had a go at it by moving the white focus box around the screen etc but it seems to have many more positions than the red focus lights through viewfinder. So, I guess the question from me is, what's the difference? Why would the camera offer only so many focus points through the viewfinder but offer so many more in live view?

[NFLD Stephen]

I'm sure someone else will chime in with a more complete answer, but the short answer is that they are two different focusing types. Through the viewfinder it is phase detect, but using live view it is contrast detect. Phase detect is much faster but it requires light to hit the focusing chip (basically when using the viewfinder some light is diverted for focusing and the rest goes to the viewfinder). When using live view, all of the light goes straight to the sensor so phase detect cannot be used. Contrast detect is done straight with the sensor.

Stephen

[clemmb]

I'm sure someone else will chime in with a more complete answer, but the short answer is that they are two different focusing types. Through the viewfinder it is phase detect, but using live view it is contrast detect. Phase detect is much faster but it requires light to hit the focusing chip (basically when using the viewfinder some light is diverted for focusing and the rest goes to the viewfinder). When using live view, all of the light goes straight to the sensor so phase detect cannot be used. Contrast detect is done straight with the sensor.

Stephen

Stephen, You did a great job of explaining it. The phase detect is much faster and works in lower light. Also works with AI_Servo for tracking moving objects.
For sports or low light this is your best bet.

[Dave Throgmartin]

The 6D doesn't have as many focus points as many Canon cameras. Overall autofocus accuracy has been quite good for me though in the center. The other AF points have also been reasonably accurate when they achieve focus, but sometimes they don't focus.

Dave

[peety3]

So, I guess the question from me is, what's the difference? Why would the camera offer only so many focus points through the viewfinder but offer so many more in live view?

Viewfinder focusing uses phase-detect AF as others have noted. The main mirror is translucent; some of the light passes through the main mirror and then reflects off the secondary mirror down to the AF sensor. There's some beam-splitting magic going on so the light arrives onto two different places of the phase-detect AF sensor for each "point", allowing the phase differences to be checked. These phase sensors are very task-specific, as they can tell not only IF focus is achieved, but if not, they know WHICH WAY TO GO to achieve focus.

Live-view focusing uses contrast detection techniques on the main imaging sensor. The selection box defines which pixels are sampled for contrast. When you request a refocus, the AF motor "runs the gamut" from <here> to full-infinity to full-macro, sampling the contrast as it goes. Once it's done a full sample, it (should) return to the point that had the most contrast. As such, it's "very easy" for the contrast-detection "action" to select almost arbitrary pixels for use as the CD region.

[Squidy]

Hmmmm... I think I understand. Is there any way to get a similar view like viewfinder (the red dots) up on liveview? I do like the way viewfinder works, but I find it difficult while looking through to select the focus point I want

[conropl]

...Is there any way to get a similar view like viewfinder (the red dots) up on liveview?

Nope.

Live view lets you move the box around to where you want to focus (and meter), and allows you to zoom in 5X and 10X at the box to aid in pinpointing your focus and metering area. But you cannot simulate or chose your red dot focus points like you see in the viewfinder.

Pat

[Anthony M]

Hmmmm... I think I understand. Is there any way to get a similar view like viewfinder (the red dots) up on liveview? I do like the way viewfinder works, but I find it difficult while looking through to select the focus point I want

There's actually advantages to both ways, I'm realio trulio hardwired to look through the viewfinder. But when I've handed my camera to other people to take shots, they stare at the back of the screen and think they broke the camera!

One thing I like about the 70D (and now 7D MkII) is that the live view/contrast detect focus is starting to become useful. It's kind of neat to have those P&S functions on a DSLR, where the little boxes scoot around and find faces for instance. It's becoming almost fast enough to use frequently, and I'm sure they will have that function very soon.

When the 6D came out, when I saw the on-paper specs for the AF I was so depressed I almost went back to Nikon. While the rest of the focus points border on useless, the center point is near magical. I shoot interiors nearly daily, and the 6D can't be beat. I can put the focus point onto a white wall, and the crazy thing can actually focus. I used to have to find some major point of contrast and recompose. I'm still a big fan of center-point focus and recomposing anyway, this just speeds up the process. You'll also find that the 6D needs very little light to achieve focus. It used to be you needed your flash just for the AF assist even if you weren't using it.