Better AF using "AF-On"???

[ricko5]

I started using AF-On (D700 and D300) about a month ago and will never go back. It now feels very natural to me.

I find that it drains my batteries a bit more regardless of VR but for the improved overall shooting experience it is well worth it IMO.

 

[PHXAZCRAIG]

There is one flaw, when you need the focus assist light from the
flash in low light, then the camera has to be in AF-S, and single
point focus.

Another flaw (though it can be a good feature sometimes) - if you are taking a self-portrait using a wireless release (Phottix Cleon, etc.), the camera doesn't autofocus. This is good if you prefocus where you want. Not so good if you're trying to get a picture of yourself in front of the Grand Canyon.

 

[duzimage]

o AF-ON gives you the flexibility of using either AF-S style
focusing (where you pre-focus, then frame, then shoot) or AF-C style
focusing where you track your subject and fire when the subject is
doing something you want to capture. And, you can freely switch
between the two without changing any camera settings. For AF-S style
focusing, you simply press the AF-ON button until focus is acquired,
release the button, reframe and then take your shot. For AF-C style
focusing, you simply hold down the AF-ON button while tracking and
shooting. In sports, this flexibility to easily switch back and
forth is very handy. On a soccer corner kick, I can pre-focus on the
ball and get a perfectly focused sequence of the kicker without
worrying about tracking at all. The very next minute, I can start
tracking focus again on the player with the ball without changing any
camera settings.

--
John
Popular: http://jfriend.smugmug.com/popular
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--
Hi Jfriend,

sory to jump into the conversation but here is my question/dilemma: I shoot action sports such as Freeride Ski, DH Mountainbike etc.... very fast, sometimes predictable movements and often specially in the woods not ver well lit scenarios. My priority is to have PERFECT focus and good framing. I mainly use 24-70mm 2.8, 70-200mm 2.8 at high shutter speed such as 1/1250s and f/wide open... I never really got into the 3D traking system even in perfect light conditions like on snow with my riders wearing bright contrasty colors. I found the red little sqare to jump all over the place leaving me with just a few shots in focus and most of the time not the right ones so I pretty much set that on a side ever since (wish it would work better because the idea is superb). So, now I've been testing my D3 set on dynamic focus, lock track "off" (so it refocuses right away), and tried 9 or 21 points (not 51 yet). Don't know which works best between 9 and 21. I guess it depends on the size of the spot I focus... my it be the head of the helmet or the t-Shirt etc....

Still, I am not satisfied with the result. I still get a lot of shots totally out of focus, and since I just simply can't believe that a powerful machine like the D3 can't keep up with this, I'm pretty sure I must be doing something wrong or that there are ways to set the full power of the D3 free.

I often have to prefocus on a spot, like a jump or rock since my rider might be hidden from my viewfinder until the last second. I prefocus to give the camera the chance to focus faster once my subject falls in but then I need it to keep focusing folowing it all the way through the "jump" let's say.

This is where I have never considered using the AF-On. In the past two days I've been reading a lot about it but have not found a true use for the type of action I need to photograph. I understand the use if your subject stays on the spot, like a baseball batter. AF-On let's you keep the focus still on your spot....but when he starts running??? Most of the time I do not have the time to reframe at all.

My needs:
1.choose my spot and where my subject will be in the viewfinder
2. choose the red little sqare

3. if possible follow the subjact as it approaches the "critical" point (a jump for example)

4. fire at will hoping it will be in focus on most of the shots and trough the entire action which most likely will be closer and closer to me (if taken frontally).

Rahter long description but wanted to be as clear as possible so that you can all give me your best advice on how to set my camera for the best result.
THANKS and sorry for my spelling (not native)

 

[AshMills]

My needs:

1.choose my spot and where my subject will be in the viewfinder
2. choose the red little sqare
3. if possible follow the subjact as it approaches the "critical"
point (a jump for example)
4. fire at will hoping it will be in focus on most of the shots and
trough the entire action which most likely will be closer and closer
to me (if taken frontally).

Rahter long description but wanted to be as clear as possible so that
you can all give me your best advice on how to set my camera for the
best result.
THANKS and sorry for my spelling (not native)

--

Sounds to me, AFC, a fixed point of focus, and a little extra stop on the lens should suffice.

A horse and rider is a deep target to focus on, at 2.8 I would imagine there's an excellent chance of the horse interfering with the rider for focus, as the horses head is in line. 3D tracking, whilst clever might struggle KNOWING which part of the (all parts moving towards you) horse and rider you want sharp.

Im afraid unless your camera is faulty it should have no difficulty getting sharp shots.

http://www.AshMills.com

 

[duzimage]

Hi Ash.

for rider I meant on Mountain Bikes or BMX.... I wish it could be a horse. Much bigger and easier to focus! I shoot sports such as ski and Mountain bike and most of the time it's on big jumps so my subject is not taking up all of my frame ince I have to shot the jump as well.

I do use AF-C and my D3 is now being checked by a Nike service center. Just to be safe but I think it's working just fine. It's a matter of right settings.
you can see some exaples here.... http://www.duzimage.com/
--
http://www.duzimage.com/

 

[jfriend00]

Hi Jfriend,
...
My needs:
1.choose my spot and where my subject will be in the viewfinder
2. choose the red little sqare
3. if possible follow the subjact as it approaches the "critical"
point (a jump for example)
4. fire at will hoping it will be in focus on most of the shots and
trough the entire action which most likely will be closer and closer
to me (if taken frontally).

Rahter long description but wanted to be as clear as possible so that
you can all give me your best advice on how to set my camera for the
best result.
THANKS and sorry for my spelling (not native)

First off, if you want good focus tracking, especially in marginal light, you have to use one of the cross hatch sensors. The other sensors just will NOT give you decent tracking performance for any sort of difficult subject. I finally just decided to leave it set on the center sensor and if my subject is off center, I zoom a little looser and crop a little in post to frame the shot. While it sounds less than ideal, it seems to give me the best AF performance and, like you, that's what makes or breaks my shots. So, that should eliminate choosing the red square.

Second off, pick a large enough part of your subject of focus on. Trying to focus on a helmet just isn't a big enough target to assure proper tracking. Pick the body of the athlete or something larger than a helmet. The helmet leaves too much of an opportunity for the focus sensor so see part of the background and/or your targeting to slop off the target onto the background.

Third, if you have good tracking technique, go with 9 points. The fewer you can get away with, the less you are leaving to chance. If you have trouble keeping one of the 9 points on the target, go with 21. I never use 51 or 51-3D as it just leaves too much to chance. Great and consistent AF accuracy will require better tracking than 51 points indicates.

Fourth, the absolute hardest thing for any auto-focus system is a target coming right at you. If you can position yourself so that's not happening, even if it's just a slight angle, it seems to do much better. I have a theory that when the subject is coming right at you, not only is the distance closing faster, but the background is fairly constant and that makes it harder for the AF system to discriminate between desired subject and background. But, if you have a slight angle to the subject motion, then the background is moving behind the subject while you track the subject and the AF system can more easily see what you're tracking and what's the background. That's just a theory, but it seems to line up with my experience. I've found that if I'm straight on with hurdlers coming right at me, I get poor AF performance. But, if I'm just 10 degrees to the side so that I'm panning with the hurdler, my AF performance goes up a bunch.

Now, you're ready for triggering AF. From the description of what you're going to do, I don't think it really matters whether you use AF-ON or not. It sounds like you want to pre-focus on a spot where a rider is going to come into view and then track from there. You can do that either by pre-focusing with a shutter half press, then release and then when the rider comes into view, go for a half press again. Or, you can pre-focus with AF-ON press and release, then when the rider comes into view press AF-ON again. There's really no advantage one way or the other. The real advantage for AF-ON comes when you sometimes want to pre-focus and then take the shot while other times you want to track focus and take the shot. With AF-ON, you can switch back and forth between the two behaviors just by how you use the AF-ON button. With a half press of the shutter, you have to physically change the AF-S switch to AF-C or back to change behaviors. If you are always tracking focus when shooting, either AF-ON or a half press of the shutter should work fine. Overtime, I think AF-ON is more flexible so it's worth learning, but it won't solve the particular problem you are asking about.

--
John
Popular: http://jfriend.smugmug.com/popular
Portfolio: http://jfriend.smugmug.com/portfolio

 

[duzimage]

Dear John, what a superb and detailled explanation.

As for the subject coming straight at you I never thought about it but what you say makes sense to me and will try, when possible.

focusing on the helmet is difficult, beliee me, specially when it goes fast. Sometimes it is necessary since the aperture is so great and there is no DOF. If the shirt of the rider is in focus but not his eyes... well, sometimes the shot does not make the cut. I try, when possible to use a wid lense and keep as much distance as possible so that I have no distracting background but my rider pretty much with good focus all over the place. Pro Action Sports photography is getting very picky about this stuff.

As I suspected AF-On would not help me that much. I basically do it the old way, prefocus by half pressing the shutter button, release and as my rider get's into the viewfinder I start tracking it. I mostly use dynamic 9 points for the same reason you say.