Author Topic: AF-S to AF-C quick change. Is it possible ?  (Read 21936 times)

Bjørn Rørslett

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #15 on: September 05, 2016, 09:45:19 »
... for me a press and release of the AF-ON button in AF-C mode is functionally the same as AF-S.
Dave

Most AF "issues" can be avoided by learning how to use AF-ON efficiently in combination with AF-C. Concomitantly it is also the requested AF-S to AF-C quick change.

Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #16 on: September 05, 2016, 10:13:17 »
Now don't lets all get confused with back button focus.
What I want to do with a D810 is this .
I usually shoot AF-S half press and then release .For about 20 seconds when a bride walks down the aisle I need to go to AF-C  and then back to AF-S without all that side button/wheel/read the screen.
Now when in AF-C it does not matter if I have to hold a button to keep it in AF-C or press and re press to change back but in AF-S I need it all on the shutter button (focus and release) .
Clearly if I had U1 and U2 it would be no problem.  I don't trust the menu on D810 as it cannot be locked.

Any thoughts ? everyone else has failed.....

I agree, for me it is also super annoying that selecting between s and c is a 'one bottom and one wheel click' (two fingers, one on each hand and both at the body of the camera) job - when it used to be just one switch one finger on one hand.

This was one of the main reasons to stay with D3 and D3X! Not upgrading to D4 when it came out!

AF on - Button - Is not the same thing at all! I know some people think it is 'the way' but not for me.

The nice image in the user manual posted here is nice - But in reality the values are this size in the display;    s    c

Not very user friendly! For fast paced work.

I'm confident Nikon will change this in new/future cameras - but unfortunately that is the current configuration....
Erik Lund

David H. Hartman

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #17 on: September 05, 2016, 21:45:14 »
I've gone back to AF-S with the AF-ON button several times over the years and I always quit shortly feeling my AF was more accurate with AF-C and the AF-ON button for static subject. AF-C with the AF-ON button for both static and moving object works for me. I don't have to think about changing the mode ever. My thumb can easily move to the AE-L/AF-L button which I map for FV Lock (Flash Value) for run and gun. The thumb knows what to do and when to do it.

I'm left eyed and my thumb rests on the bridge of my nose and on the AF-ON Button. I press the camera moderately into my face for stability. I wear glasses of the transitions bifocal type with the bifocal set low for driving a car. There is just enough bifocal to use the top and back LCD(s), no need to fumble with glasses. The only problem is I need to clean my glasses occasionally. Without these glasses I may as well to set the camera to "P" for professional and hope for the best. :)

Dave

Another advantage for me is it's really natural to switch from auto focus lenses to manual focus. The first thing I do with a new camera is get the AF off of the shutter release button.
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Anthony

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #18 on: September 05, 2016, 22:13:36 »
Part of the issue with AF-ON in AFC mode (the most useful) is that with static subjects you need to be sure that focus has settled down to the correct setting.

This is a bit of a problem with mirrorless, as AFC (which is what makes the AF-ON button worthwhile) tends to hunt, because of contrast AF.  I hope the X-T2 will address this issue.
Anthony Macaulay

David H. Hartman

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #19 on: September 05, 2016, 22:37:56 »
Part of the issue with AF-ON in AFC mode (the most useful) is that with static subjects you need to be sure that focus has settled down to the correct setting.

But what happens with AF-S? It locks but did it lock prematurely? If it did then the focus may be off enough to waste the shot. I'm speaking here of a Nikon with phase detection AF with release priority. I can't abide with focus priority except for focus trapping.

Notice that some lenses focus faster than others and this certainly appears to be tailored to the use of the lens. Many note that the Nikon AF-S 70-200/2.8(s) focus faster than the AF-S 85/1.4(s) and the new AF-S 105mm f/1.4E ED. This appears to me to be a feature of the f/1.4 lenses as they need more accurate AF while the 70-200/2.8 are often used for sports where they need to focus quickly and need to track fast moving subjects.

At the end of the day nothing is perfect.

Dave
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Anthony

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #20 on: September 05, 2016, 23:01:06 »

At the end of the day nothing is perfect.

Dave

Yes!
Anthony Macaulay

Matthew Currie

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #21 on: September 06, 2016, 00:23:32 »
Part of the issue with AF-ON in AFC mode (the most useful) is that with static subjects you need to be sure that focus has settled down to the correct setting.

This is a bit of a problem with mirrorless, as AFC (which is what makes the AF-ON button worthwhile) tends to hunt, because of contrast AF.  I hope the X-T2 will address this issue.

I have never found this to occur with the D3200, and there seems to be no measurable difference between the results when using BBF with either mode. 

It's always a little frustrating since Nikon does not tell us everything and only hints at it.  We are told that in AFC the auto focus is more forgiving, without really letting us know whether this means that the actual AF is sloppier or just the focus priority less rigorous.  A quick and unscientific test suggests that with BBF there's no measurable difference between the two on a static subject. 

In any case, though, I've been using BBF for some time, and have never found it to hunt in AFC.  It's impossible to test how it might behave in Live View because BBF does not work at all with continuous focus (AFF in LV) anyway.


Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #22 on: September 06, 2016, 09:12:07 »
But what happens with AF-S? It locks but did it lock prematurely? If it did then the focus may be off enough to waste the shot. I'm speaking here of a Nikon with phase detection AF with release priority. I can't abide with focus priority except for focus trapping.

Notice that some lenses focus faster than others and this certainly appears to be tailored to the use of the lens. Many note that the Nikon AF-S 70-200/2.8(s) focus faster than the AF-S 85/1.4(s) and the new AF-S 105mm f/1.4E ED. This appears to me to be a feature of the f/1.4 lenses as they need more accurate AF while the 70-200/2.8 are often used for sports where they need to focus quickly and need to track fast moving subjects.

At the end of the day nothing is perfect.

Dave

AF-S mode predicts and acquires precise focus by design.

AFS 1.4 lenses has less fast AF as to ensure and acquires precise focus by design.
Erik Lund

Ilkka Nissilä

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #23 on: September 06, 2016, 12:51:51 »
The purpose of AF-S mode is that the camera focuses until it decides it has acquired focus, then stops and you can do your recomposing which was the default way of doing things in the early years of AF when there was only a single point (or the peripheral points were not so sensitive). By default, AF-S mode is associated with focus priority. I guess when you combine AF-S mode with release priority, you should be able to interrupt the process of focusing by taking a shot before the camera has finished acquiring focus. I have never tried this combination of settings though.

I stopped using AF-S mode when I had the D70 and the resulting focus accuracy was poor. The camera would often decide it was in focus when it was not. In AF-C mode with AF-ON, I could wait until I could see the subject in focus and take a few shots, and the result was clearly better. In more advanced cameras AF-S worked much more reliably at that time, but I wanted to operate all my cameras in the same way, so I started using AF-ON with AF-C and release+focus priority (release priority if release+focus is not supported). This has worked well as I don't have to change settings if the subject is static vs. moving, and release+focus priority waits a little bit between shots to acquire focus before releasing, but does not interfere with focus + recompose if the subject is still, I can still use that to achieve more off-centered compositions. I monitor the sharpness in the viewfinder and take what I see into account in timing my shots. I'm aware that for static subjects AF-S with focus priority would probably give a higher percentage of focus keepers but I don't like the fact that the camera decides when focus has been achieved - I want to decide when the shot is taken, and I base that decision on what I see in the viewfinder. The timing may be slightly delayed by the camera if it wants to keep focusing a bit but this has not prevented me from timing shots based on focus and subject expression.

The bride (or bride and groom) walking on the aisle before and after the wedding ceremony can be one of the most difficult subjects to photograph. This is because the corridor has often poor lighting and behind the subject there can be bright light and structures (church altar, wall texture etc., or the outer door) which are attractive to the AF systems rather than dark faces in the center of the picture.  ;) In particular the church I was at last time had brightly lit wall behind the altar and there was complicated texture in it (it is a medieval church). I think the safest place for the focus point in this circumstance would be to point it at the middle of the body (as then the wall carvings would not be near the active AF point, also center points are the most reliable in focusing), but I have a habit of placing the focus point on the face so that focus is accurate even when using fast lenses (f/1.4, f/2). In the corridor shots I typically use the 24-70 because it can accommodate different framings in a fast changing situation and focuses quickly. As usual my camera is in release+focus priority and I press AF-ON to keep focusing while I take the shots. Typically I get maybe one third of slight focus misses in this situation because there is not enough light and contrasty detail in the bride's face vs. bright textured wall in the background. Also the light level can be very low, ISO 6400 is not enough to get correctly exposed blur-free shots, and I've resorted to 12800. With the D810 this looks so-so, but with the D5 the results look ok even in colour.

Flash is another option for this situation. A flash unit typically has a built in focusing assist light but that only works (if I'm not mistaken), in AF-S mode with center point AF. I have read it being recommended that the aisle shots be made using the support of the focus assist light but of course then there is the problem that the bride (or bride and groom) may be moving more quickly than would be ideal for photography.  ;) I am staying with the AF-C + AF-ON method but am considering moving my focus point to the center row in order to avoid distraction by the highlighted textures in the background. I suppose I could try the focus assist light method at some point. I just don't like the idea of having to switch to single servo focusing especially when the subject is moving.  Incidentally the recommendation I've read for this situation also includes use of the flash itself to light the main subjects, but I tend to go with available light.  It can be debated whether the flash fits in this situation (it would help reduce movement blur on the front side of the subjects, but a point light source adds sharp reflections and emphasizes skin pores which I don't like). I guess the available light can be regarded to be of poor quality as well, so it is a choice out of two not so great options. Anyway, I wanted to mention this because if the OP prefers to work in AF-S mode (shutter button activated AF), perhaps single servo focusing with focus assist light from a speedlight would work acceptably. I guess the key is how much depth of field you have, and how quickly the bride (or bride and groom) are walking. ::)


Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #24 on: September 06, 2016, 14:06:42 »
Quote from Nikon:

However, maintaining focus doesn't guarantee a sharp image, as there is a short time lag between the release of the shutter and the capture of the picture. To solve this problem, the focus tracking system is a predictive system that uses special algorithms to forecast the position of the subject at the moment the image is captured. The prediction is based on a measurement of the subject's movement and speed

As far as I have experienced this is the case for both AF-C and AF-S mode.

And I know it is the case also for the lens itself, the CPU in the lens tell the camera where to stop the focusing motor for best stopping/decelerating the motion of the actual focusing elements for that particular lens, it's build into the calibration of each lens after a run on the test stand where the lens is set to try several runs, too far - too close, to obtain best focus, from both directions.

The camera in AF-S

Push focus button;

The AF sensor picks up the brides motion and see if she is approaching or leaving and her speed and distance to her.

The camera AF sensor also picks up that the lens is either focused too far or too close and by how much.

Camera calculates where will the bride be when the lens finish focusing and then predicts when to open the mirror and fire the first curtain,,,
Erik Lund

ArendV

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #25 on: September 06, 2016, 16:36:42 »
Erik, I would really be surprised if this Nikon quote also applies to AF-S, I think it is AF-C only.

In single-servo AF (AF-S), focus will lock if the shutter-release button is kept pressed halfway and no focus tracking is happening.
And in my experience with even the slightest movement AF-S will off.
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Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #26 on: September 06, 2016, 16:47:10 »
The camera is predicting where the target will be in AF-S

The camera is tracking and predicting where the target will be in AF-C
Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #27 on: September 06, 2016, 16:51:52 »
With AF-S there is no predicting and to me there also should not be, it should be static.

Your quote is coming from the Nikon site on 3D Focus Tracking
http://www.nikonusa.com/en/learn-and-explore/article/ftlzi4lx/3d-focus-tracking.html
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Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #28 on: September 06, 2016, 17:12:05 »
Yes it is taken from the 3D.

But AF-S would miss the target if it didn't predict in the same way when the actual exposure will occur.

Imagine a race car full speed, how would the exposure be at the correct moment when the target enters the focus plane if there was no prediction done in camera,,, just like AF-C need prediction on top of traction to nail it.
Erik Lund

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Re: AF-S to AF-C quick change. Is it possible ?
« Reply #29 on: September 06, 2016, 17:20:49 »
Erik, that is indeed my experience that AF-S will miss the target with the slightest movement of the object between half press and actual exposure.
But probably good to have some others step in this discussion to resolve it.
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