Auto-Focus Points - how do I use them?

[Iron Flatline]

Hi everyone.

There is another thread in the Beginners Section about AF points, but sometimes threads there don't get enough serious traction.

So all the new cameras have a huge amount of AF points - 9, 19, 51... but all I've ever done is used the center point. I focus, recompose, and shoot.

Now, it occurs to me that there's some really useful functionality that I'm not including in my shooting.

How do you all use the AF points? What can you tell the rest of us about them? My new camera even has a quick menu for changing AF points - why might I want to do that?

Please advise.

 

[Hawaii Five-O]

Yeah i have those on my camera too, I can use my little joystick button to open the focusing grid. I have to read more about it for my camera, but I'm guessing on mine that the center part of the grid is the eye level horizon plane. And if I want to focus in on something above eye level I highlight the top part of the grid, and it will focus on all objects at the top of the frame.


Edit: I was playing around with it and that is how it works. I highlighted the rigth side of the grid and it only focuses in on objects on the right side of the frame.

 

[tirediron]

I use all of the AF points in my D300 (51 of them) but only one at a time (except for the rare occasions I shoot full auto). I compose the image, and then using the control button on the back, select the AF point which is over the point in the scene that I want as my key focus.

 

[Hawaii Five-O]

On my Elan 7 it has a laser that reads my eye to see what I am looking at and focuses on that. Its like a 2 for 1 deal it focuses and gives free Lasik:thumbup:

 

[Overread]

I use all of the AF points in my D300 (51 of them) but only one at a time (except for the rare occasions I shoot full auto). I compose the image, and then using the control button on the back, select the AF point which is over the point in the scene that I want as my key focus.

I do this as well.
even though I have far fewer points and do this far less than often this is how I use them. I don't trust my 400D to use all the points and choose the point of focus for me - mostly as twigs and leaves are often between me and my subject - were I shooting birds in flight in an open field I could see myself using all the points.

 

[K_Pugh]

Yeah i generally use the centre focus point 90% of the time.. focus, recompose, shoot. If i'm shooting action (panning) i'll change the focus point then. Say for instance i'm shooting my dog running, i'll change the point to where i want his head to be (my focus point) allowing the rest of the body to be in the frame.

What i don't get or use is this Dynamic AF thing where is selects several points at once?

 

[Dao]

If I taking a photo of a still object that is off the center and I am using a tripod, I will use a "Selected" AF point. (BTW, I have the Canon 9 points system).

In general, I will just using the center point and recompose. It is because if I use all of them, the camera did not always choose the one I want. And I read a article somewhere, in some situation, "AF center -> recompose -> take the shot" may not be a good idea.

If I am remember correctly, it said the distance between the camera and the object when the object is in the center of the image is different when it is off center. I know, the different is very little, but that is what I read.

Also, I sometimes use the auto focus point to help my composition. If I like to make the horizon look level, I will use those points as a reference.

 

[Dmitri]

Birds in Flight.

 

[roadkill]

On my Elan 7 it has a laser that reads my eye to see what I am looking at and focuses on that. Its like a 2 for 1 deal it focuses and gives free Lasik:thumbup:

That's an interesting option. I don't think I could use such a function simply because even once I compose and even have my focus, I generally like to reread the scene over befrore I pull off the shot. Although i guess you probably have some kind of focal lock on that camera.
I don't really use my different focal points. Recomposing seems the quickest option.

 

[roadkill]

Aahhhh.... Tripod shots. Duh. guess that makes sense.

 

[Village Idiot]

Hi everyone.

There is another thread in the Beginners Section about AF points, but sometimes threads there don't get enough serious traction.

So all the new cameras have a huge amount of AF points - 9, 19, 51... but all I've ever done is used the center point. I focus, recompose, and shoot.

Now, it occurs to me that there's some really useful functionality that I'm not including in my shooting.

How do you all use the AF points? What can you tell the rest of us about them? My new camera even has a quick menu for changing AF points - why might I want to do that?

Please advise.

Also, depending on the camera, it acts as the metering position. If you have spot metering, it will meter over the active AF point.

So if you're shooting a white male in all black clothes against a black back drop and AF/spot meter on the person's face, the camera will only expose for the face and will not consider the black clothes and black backdrop.

I use all of the AF points in my D300 (51 of them) but only one at a time (except for the rare occasions I shoot full auto). I compose the image, and then using the control button on the back, select the AF point which is over the point in the scene that I want as my key focus.

Doesn't the D300 only have so many actual AF points and the rest are helpers? I didn't think you could pick through all 51.

 

[kellylindseyphotography]

I don't focus/recompose because when I was doing that, my camera was missing the focus half (yes, about HALF) the time. Thats a lot of missed shots. Aside from everything else in a picture, if you miss your focus, the shot is garbage. Everything else is subjective (subject, compostion, light to some measure etc).. but missing focus is not an option.

I use the back button focusing but don't toggle. I don't need more buttons to press when I'm chasing a toddler on a shoot. BBF seems to get the job done, and well

 

[kundalini]

Doesn't the D300 only have so many actual AF points and the rest are helpers? I didn't think you could pick through all 51.

The inner 15 sensors (3columns x 5rows) detect contrast in both horizontal and vertical axis. The remaining 36 (split on either side at 3columns x 5rows + 1column x 3rows) detect contrast in the horizontal axis only when held in normal position.

 

[Big Mike]

I don't focus/recompose because when I was doing that, my camera was missing the focus half (yes, about HALF) the time.

This can sometimes be caused because you change the distance to the subject when you recompose...but it only happens when shooting with a very shallow DOF and at close distances. If you are missing half of your shots while focusing & recomposing...then you must be doing something wrong...like keeping AF active or not locking it before recomposing.

 

[Big Mike]

I use the centre point and focus & recompose. On my camera, only the centre point is a cross type sensor, so I trust that one to work better than the others.