Yet another AF-ON question

Started Apr 28, 2008 | Discussions
carauction Veteran Member • Posts: 6,646
Yet another AF-ON question

D300, Using AF-ON for focus, with C-AF and 9 or 21 point Dynamic Area.

If you press the AF-ON button once and take your finger off, you have a locked focus. This focus was acquired though, using a 9 or 21 point area, NOT a single point. Because of this, aren't you possibly giving up some accuracy?

replies appreciated,

mike

Gary Elliott Regular Member • Posts: 280
Re: Yet another AF-ON question

Yep, the press & release triggers a quick focus using whatever criteria you selected - 9, 21, etc.

I use this all the time now that I've gotten used to it. Started using it on my D70 for sports based on suggestions from a lot of skilled photographers in this forum.

When I moved to the D300 the only challenge was a tendency for my highly-trained thumb to reach past the AF-On button to the AE/AF button That sure caused some concern for a few minutes

Gary

Humanoid
Humanoid Veteran Member • Posts: 4,666
Re: Yet another AF-ON question

Depends, are you using Single area AF or Dynamic area AF or 51pt, not to be confused with Continuous servo and single.

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Ray

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OP carauction Veteran Member • Posts: 6,646
Re: Yet another AF-ON question

Humanoid wrote:

Depends, are you using Single area AF or Dynamic area AF or 51pt,
not to be confused with Continuous servo and single.

Hi Ray

Using Dynamic.

Mike

Peter Davis Senior Member • Posts: 1,171
Re: Yet another AF-ON question

What do you mean by giving up accuracy?

If 9- or 21-point are less accurate, shouldn't it be the same whether you're using AF-ON or not?

Richard Southworth Regular Member • Posts: 485
Re: Yet another AF-ON question

Mike,

The answer is "it depends". I use AF-ON exclusively, and discovered a possible trap in using dynamic area 9/21/51. At the point you press AF-ON the camera trys to "lock on" to the whatever object is in the selected focus area. If you acquire focus and release AF-ON without shifting the camera you will have locked the focus on that object.

However, if you press AF-ON while one object (say an eye) is in the selected focus area, and without releasing AF-ON move to another object (for example the other eye), the camera will try to remain focused on the first object by using another focus area. This won't show in the viewfinder (ignoring 51pt. 3d in this discussion), but will show as a red focus indicator in the LCD after the shot. My normal mode is to press AF-ON early and swing the camera to pick the desired focus object, so I don't normally want to the camera to be "sticky". I also have the lock-on setting at off.

I leave the camera in single area focus as a rule, and only move to dynamic when there is a reason, i.e. tracking moving subjects when it may be easy to slip off of the initial focus object. And I leave the camera set at 9 pt. to maximize performance if I do go to dynamic area.

Richard Southworth

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Tim Updegrove Regular Member • Posts: 330
Re: Yet another AF-ON question

Since you are using 9 or 21 point Dynamic Area, I assume you are taking an action photo where the subject is moving and that you are using Continuous Servo. So, if you take your finger off of AF-ON, then you are telling the camera that the subject is in focus and will remain in focus until you press the shutter. That is, the subject has stopped. If the subject is still moving then you should keep holding the AF-ON and press the shutter at the appropriate moment to take the picture.

D300, Using AF-ON for focus, with C-AF and 9 or 21 point Dynamic Area.

If you press the AF-ON button once and take your finger off, you have
a locked focus. This focus was acquired though, using a 9 or 21
point area, NOT a single point. Because of this, aren't you possibly
giving up some accuracy?

Tim Updegrove Regular Member • Posts: 330
Richard

Good point. In your eye example, I guess you just need briefly release the AF-ON when switching eyes.

However, if you press AF-ON while one object (say an eye) is in the
selected focus area, and without releasing AF-ON move to another
object (for example the other eye), the camera will try to remain
focused on the first object by using another focus area.

OP carauction Veteran Member • Posts: 6,646
Re: Yet another AF-ON question

Richard Southworth wrote:

Mike,

The answer is "it depends". I use AF-ON exclusively, and discovered
a possible trap in using dynamic area 9/21/51. At the point you
press AF-ON the camera trys to "lock on" to the whatever object is in
the selected focus area. If you acquire focus and release AF-ON
without shifting the camera you will have locked the focus on that
object.

However, if you press AF-ON while one object (say an eye) is in the
selected focus area, and without releasing AF-ON move to another
object (for example the other eye), the camera will try to remain
focused on the first object by using another focus area. This won't
show in the viewfinder (ignoring 51pt. 3d in this discussion), but
will show as a red focus indicator in the LCD after the shot. My
normal mode is to press AF-ON early and swing the camera to pick the
desired focus object, so I don't normally want to the camera to be
"sticky". I also have the lock-on setting at off.

I leave the camera in single area focus as a rule, and only move to
dynamic when there is a reason, i.e. tracking moving subjects when it
may be easy to slip off of the initial focus object. And I leave the
camera set at 9 pt. to maximize performance if I do go to dynamic
area.

Richard Southworth

I follow you Richard.

What I am basically asking is this: Set in AF-C & dynamic 9 or 21 point, focus on subject... release AF-ON immediately , would there be a better chance of accuracy if you happened to be in single area focus mode at the time?

Mike

OP carauction Veteran Member • Posts: 6,646
Re: Tim

Same reply as to Richard:

What I am basically asking is this: Set in AF-C & dynamic 9 or 21 point, focus on subject... release AF-ON immediately , would there be a better chance of accuracy if you happened to be in single area focus mode at the time?

Mike

P.S. Just to confirm that we are on the same page....I am no longer tracking at this time, still in AF-C, but shooting a static subject now.

Tim Updegrove Regular Member • Posts: 330
Re: Tim

I understand your question but I'm not an expert on the algorithm (just begun reading Thom's eBook). A scenario like you describe might be a BIF, which you are tracking, but then it lands on a branch. While static on the branch, you press and release AF-ON. I'm guessing that if there is no movement (static object) then the focus point used should be the one you placed on the subject in the viewfinder. That is, without movement, there would be no reason for the AF to shift to one of the other AF points.

Richard Southworth Regular Member • Posts: 485
Re: Yet another AF-ON question

No, not in my experience. A long as you start and stop AF-ON with the same object in the selected focus area, then AFAIK there is no difference than using single area. Make sure a4 (Lock on) is off unless you are specifically shooting moving subjects with the possibility of interfering objects; one of the worst "mistakes" Nikon has made is shipping the camera with a4 enabled, has caused a lot of grief, since it is pretty much just a delay in focusing when moving from one object to another.

I also advocate "release priority" for AF-ON in continuous mode with focusing disabled on the shutter release. In my experience, the less the af system has to "worry about" the better, just have to trust your eyes and the camera and not worry about the focus dot. And for walking around ready to shoot whatever, leave it in single area, not dynamic, to avoid the false focus problem already described.

Richard Southworth

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Jeff Diaz Contributing Member • Posts: 593
Focus will only be accurate if you know the subject was

in focus at the time you let go of the AF-ON button. All this is assuming that you have set the camera to use AF-ON only to activate AF (i.e. shutter release button set to not activate focus). I set my cameras to AF-C and Dynamic AF with release priority and AF Lock on set to off.

Under the above condition, to properly use the AF-ON technique, the first thing is to put the selected starting AF point over the selected target. If one activates AF-ON before doing this, then one runs the risk of starting focus on an object other than the subject of interest.

Once the starting AF point is on the target, hold down the AF button until the camera acquires focus (i.e. the target looks sharp in the viewscreen or you get green light ( o ). Now if you let go of the AF-ON button, AF is stopped and the focus distance remains fixed even when you recompose. This is the same as running the camera in AF-S single area AF -- even if the camera is set to AF-C 9 point or 21 point Dynamic AF, the focus is first achieved using the selected AF point. Dynamic AF does not start up until an initial focus on target has been achieved.

However, if one continues to hold down the AF-ON button, the camera continues functioning in dynamic AF 9, 21, 51, or 51 point3D dynamic area AF tracking. The minute one lets go of AF-ON, focus stops at the last point of sharpest focus as determined by the camera.

Now while continuously holding down AF-ON to activate dynamic area AF tracking, if one looks through the viewfinder with the right eye and keeps the left eye open to see the action outside of the viewfinder, one can anticipate when a obstacle will cross in front of the target. By judiciously releasing the AF-ON button while repositioning the selected AF point back over the target, one has effectively achieved an "AF lock on" of whatever duration and the minute the obstacle uncovers the target, pressing and holding AF-ON down reactivates AF and then tracking.

I do this all the time with basketball, soccor, wildlife shooting and maintain a 80%-90% in focus accuracy during a shoot. This technique is far more flexible than leaving the camera in AF-S single area AF or having AF tied to the shutter release button. One isn't giving up any focus accuracy once one learns the technique. I cannot realistically achieve a 100% focus accuracy rate because there are times when I'll roll my finger over the shutter release when anticipating the action and trying to get an insurance shot of something even if it is slightly out of focus.

carauction wrote:

D300, Using AF-ON for focus, with C-AF and 9 or 21 point Dynamic Area.

If you press the AF-ON button once and take your finger off, you have
a locked focus. This focus was acquired though, using a 9 or 21
point area, NOT a single point. Because of this, aren't you possibly
giving up some accuracy?

replies appreciated,

mike

OP carauction Veteran Member • Posts: 6,646
Re: Thanks Tim & Jeff

Mike

theresa Regular Member • Posts: 224
Re: Focus will only be accurate if you know the subject was

bookmarking thanks Jeff

OP carauction Veteran Member • Posts: 6,646
Re: Jeff D.

In essence, the following is a direct answer to my initial question:

"Now if you let go of the AF-ON button, AF is stopped and the focus distance remains fixed even when you recompose. This is the same as running the camera in AF-S single area AF -- even if the camera is set to AF-C 9 point or 21 point Dynamic AF, the focus is first achieved using the selected AF point. Dynamic AF does not start up until an initial focus on target has been achieved."

Thanks

Mike

egrivel Senior Member • Posts: 1,840
Re: Yet another AF-ON question

Richard Southworth wrote:

[... about using AF-ON and dynamic area 9/21/51 (non-3D) modes...]

However, if you press AF-ON while one object (say an eye) is in the
selected focus area, and without releasing AF-ON move to another
object (for example the other eye), the camera will try to remain
focused on the first object by using another focus area. This won't
show in the viewfinder (ignoring 51pt. 3d in this discussion), but
will show as a red focus indicator in the LCD after the shot.

I've had a hard time trying to reproduce this. It seems that in dynamic area, the camera only tries to "hold" the focus for a very brief period of time, maybe 1/3 of a second. After that, it re-focuses on what is now under the selected focus point.

So if I start out with the center focus point in dynamic area 21 point, and focus on object A, then move the camera to point at object B, the camera will wait for a few moments before focusing on object B. If I click the shutter during those few moments, the focus point that is now over object A will be highlighted in the review, but if I wait a little bit longer, the camera will refocus and now object B will in focus. I keep the AF-ON button pressed all the time.

I thought the point of dynamic area was that the camera keeps the originally selected object in focus, using another focus point. However, only 51point 3D focusing seems to actually do this. However, I've read that 21 point is better to track something than 51 point 3D mode?

Am I missing a setting somewhere, or do I have the wrong expectations of the focusing system?

My settings:

  • Focus mode: continuous servo AF (C)

  • AF Area mode selector: Dynamic area AF (middle position)

  • AF Area Mode: 21 points

  • setting a1 (AF-C priority selection): Release

  • setting a3 (dynamic AF area): 21 points

  • setting a4 (focus tracking with lock on): off

  • setting a5 (AF activation): AF-ON only

  • setting a8 (AF point selection): 51 points

Eric
--
http://www.lumenssolutions.com/photography/

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