# Idiot question alert - 52 focus points

Started 11 months ago | Questions thread
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 Re: Pretty simple actually ... In reply to SergioSpain, 11 months ago

SergioSpain wrote:

Grevture wrote:

Well, in most cases you want to be able to do both. That is why we have options like matrix exposure where the camera makes lots of measurements and analyze the result in various ways, and also simple spot metering where you measure at one point only.

Focusing works pretty much the same. Sometimes you just want to measure in one spot and completely ignore what is going on around that spot. Sometimes you want to measure over a smaller area, and ignore things outside that area. And sometimes you want to measure over a larger area and figure things out from all that information.

That's a bit misleading though. You can take an average exposure reading and shoot with that, but there's no such thing as an average focus reading. And if there were, it wouldn't work in most cases! If you have all 51 points active, it doesn't mean that the camera is using focusing information from all the points. It means that if the subject is moving, the camera can try to track it and keep it in focus using one of the 51 points. The various points can also be used for predictive tracking to predict where the subject will be and where the focus will be when the shutter is triggered. But again, there is no such thing as average focus.

Just to add to the confusion . . . LOL

There is only one focus plane that is in focus.

That's what you are trying to decide, is where the focus plane is.

So when you use a single point, whatever is at that point is where the focus plane ends up.

When you use more points, you give some control over to the camera on where to place that focus plane. That's when you take the shot and you think . . . that's not what I wanted to be in focus. <grin>

So . . . if you "know" where you want to put that focus plane (and you have the time) use single point, point at something that is at that plane (or manual focus) and focus on it.

You're aperture then decides how much in front and behind that plane is in focus.

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