Auto focus area?

[jamesdavidboro]

Whats the point in the Wide Auto focus area? Surely the camera can't focus on more than one distance at a time so whats the point of it? I've heard it suggested that useing it for moving subjects can be benefit, but for moving subjects i just click onto continuous AF and leave the area on local.

 

[Robin Usagani]

Lets say you have 9 focus point and you turned on all of them. The camera will try to find the closest one from you. The reason you want a wide focus are is so you dont miss. Lets say you only have 1 focus point turned on. Lets say you are shooting a bird flying. If you dont put that one point on the bird, you will miss focus. But if you have 9 or more focus point turned on, you probably will hit the bird. But sometimes having so many focus point will hurt you if all of the sudden there is something on the foreground of the subject. It will focus on that.

 

[jamesdavidboro]

Right so really it could be useful if you're tracking something on a blank background, like a bird against the sky, but apart from that it could be a hinderance. Thanks for the explanation. Do you ever use it yourself?

 

[Big Mike]

Whats the point in the Wide Auto focus area? Surely the camera can't focus on more than one distance at a time so whats the point of it? I've heard it suggested that useing it for moving subjects can be benefit, but for moving subjects i just click onto continuous AF and leave the area on local.

If you are talking about the mode where the camera is allowed to choose from any of the focus points, then I agree that it's not a good way to go.
And yes, it's impossible for the camera to focus on more than one distance or plane. When you get more than one focus point to light up, it means that both those points are over something that is the same distance away from the camera.

Of course, there are situations where it might be beneficial...fast moving subjects may be one of those. High end cameras actually have many more focus areas than shown in the viewfinder, and they can be very good at tracking a subject while it moves around in the FOV.

But in the end, the camera can't really know what you want to focus on, so it's probably best to choose the point and focus on what you want to.

 

[Robin Usagani]

All the time. Very easy to turn on all of the focus pt on my 5D. When I do portraits usually only 1 pt.

 

[Derrel]

The Nikon D2-series bodies had a very wide-area AF system option that allowed Group Dynamic AF focusing, with or without closest subject priority, and with variable timing on Lock-On, to determine how long the AF system would stay locked on to its current target when "new" targets came into the viewfinder...it worked AMAZINGLY well.

By allowing the camera's AF system to analyze multiple data points, it can help in tracking rapidly-moving subjects/targets. Turning OFF all the AF points, except for the center point, limits the amount of data that the AF system has at its disposal. Using a wide-area AF system,with multiple AF points active and enabled, allows the AF system to compute the distance, and direction, of motion by using comparative analysis. Turning OFF all the AF points and relying on only the central AF point means that there is just ONE point being analyzed, and other additional information is not being considered. That can lead to problems when a subject's motion is fast, or erratic, or when the photographer wishes to use an off-center framing of the subject.

Nikon cameras have color-sensing sensors (between 420, 1,005, and 2,016 separate sensors) that measure subject COLOR, and correlate that to the AF area selected by the user when acquiring initial focus, and then use the color info (R-G-B data) to track targets that the user has initially selected. Canon is slowly developing its own system to do the same thing using an R-G-YG-B system in its high-end cameras, and the 7D and 60D.

There is a huge difference in the way Nikon and older Canons and other color-blind systems focus in group-AF modes, and even within brands, each specific focusing module has its own quirks.

 

[mrpink]

I use single point AF 90% of the time. Target what you want entirely in focus (on portrait work, generally the eye of the subject) Half press the shutter to AF and lock it, then recompose and shoot. Takes some getting used to, but works well for me.

As stated, for faster moving subjects, multipoint or 3D tracking is used.





p!nK

 

[classcams]

The key to all this focus business is the "hyperfocal distance " the formula being " FL^2/ (a*Cof C) /1000" to bring it to meters.

 

[enzodm]

The key to all this focus business is the "hyperfocal distance " the formula being " FL^2/ (a*Cof C) /1000" to bring it to meters.

Only if you need having all in focus, which is not always the case. I would better say not often.