AF-S to AF-C quick change. Is it possible ?

[simsurace]

I would guess that there can only be prediction in AF-S if the shutter release is fully depressed, since that is when the camera has full control over when to shoot the picture and therefore it can put the focus where the subject is predicted to be at that time. But with standard usage of AF-S the photographer can wait an undetermined amount of time after half-pressing and before he/she presses the shutter release, so I don't see any way to accurately predict where to put the focus other than where the subject was measured in the first place.

Please consider that I'm just speculating since I don't know how Nikon's algorithms are set up.

[Matthew Currie]

I have only read of predictive focusing as a function of AFC, and have difficulty imagining how it could work in AFS, and why one would want it at all.  Since AFS allows the user to choose a focus point that will not change when you recompose, and that need not fall within any of the designated focusing areas, or for that matter even in the final frame,  how would the camera track it, and would it not defeat the purpose to have the camera second guess your choice?

[Erik Lund]

You misunderstand.

You should not just half press and wait in AF-S,,, that is not the point.

You push the shutter all the way when you want the image,,,

[Matthew Currie]

You misunderstand.

You should not just half press and wait in AF-S,,, that is not the point.

You push the shutter all the way when you want the image,,,

I wonder if there is a communication issue here.  If you focus and recompose in AFS, and are not using the back button, then you must half press and wait at least for as long as it takes to settle on a composition. I would expect when doing this that the focus point would remain exactly where I initially put it, and would be unpleasantly surprised if the camera tried to guess my intentions, and otherwise surprised if it were able to do so when my initial focus point falls outside the camera's chosen focus areas.  If one could not do this, what would be the point of having AFS at all?

[Erik Lund]

I would guess that there can only be prediction in AF-S if the shutter release is fully depressed,,,,

Yes exactly!

[David H. Hartman]

I find AF-S almost useless for taking a photo of a moving object. The camera may estimate the distance the subject will travel before the shot is taken if the shutter release is fully depress at the outset. In that case the camera determines when the shutter is release. AF-S can be used for "manually trapping" the subject as one might do with a manual focus camera: F, F2, F3 but there is no advantage over AF-C and the AF-ON Button. AF-S for a moving subject precludes shooting a burst as only the first shot will be in focus. My cameras are always set to continuous advance and the low advance speed is bumped to five or six frames per second is available. I normally squeeze off single frames.

I honestly don't see any reason to photograph a moving subject if AF-S mode other than that the way the camera is set and there is no time to change to mode to AF-C. This is where AF-C and the AF-ON button allows one to switch from "AF-S" like use to AF-C at the speed of reflex, even faster than conscious decision. There is no way to switch from AF-S to AFC mode that as fast. There is no way to switch that is as error free.

Yesterday I was photographing my friend's cockatoo. The bird will stand in the same place sometimes for several minutes but it's not standing still. It will shift it weight from foot to foot and move it's head. It's motions are such that a 105mm lens at f/5.6 doesn't have enough DoF to cover for this motion. Not only that but the space I'm photographing the bird in is built like an orchid house so light levels are reduced. The subject distance is generally about 1.5m. Shutter speeds are frequently between 1/250 and if lucky 1/500. The object is always to get an eye in focus. The decision of when to lock focus can't be left up to the camera. AF-S mode is next to useless. The camera can not possibly predict this kind of erratic and punctuated motion. I'm actually able to get some photos in focus with a 105/2.8 AIS Micro-Nikkor under these condition but the AF-S 105/2.8G ED Micro-Nikkor has sharply increased the number of in focus shots close to 50%. Then there is loss though subject motion. Many focus attempts do not result in a shutter release as I know the bird has moved and will be out of focus. I hope this is keeping my reflexes sharp as I have little time for photography other than my bird sitting. It helps that the bird likes me and calls me by name, "Hi David." Unfortunately my friend won't allow me to photo photographs of her bird on the internet.

Some thoughts on Focus Priority. When the original Minolta Maxxum came to Los Angeles a camera salesman friend called me and told me the Maxxum was in. When I got a chance with the camera I picked a subject. The camera focus on it but since it only offered focus priority it would not let me take a photo. I knew the camera had focus correctly but the camera didn't. I didn't even have to recompose to mess up the camera. For most use I find focus priority useless. Trap focus comes to mind but nothing else.

I've typed too much so it's time I just sit back and read.

Dave

Sorry about the typos as I'm out of time.

I'm glad there are modes that satisfy others even when I don't use them. It's good when a camera can be adapted to many different ways of using it.

[paul_k]

I wonder if there is a communication issue here.  If you focus and recompose in AFS, and are not using the back button, then you must half press and wait at least for as long as it takes to settle on a composition. I would expect when doing this that the focus point would remain exactly where I initially put it, and would be unpleasantly surprised if the camera tried to guess my intentions, and otherwise surprised if it were able to do so when my initial focus point falls outside the camera's chosen focus areas.  If one could not do this, what would be the point of having AFS at all?

Well, I really did my best but I didn't find any mentioning on the several Nikon tech sites of predictive AF possible with AF-S

In this article http://www.nikon.com/about/technology/rd/core/software/caf/index.htm , it is only mentioned in combination with AF-C, just like in this article http://www.nikonusa.com/en/learn-and-explore/article/ftlzi4pn/51-point-autofocus-system.html#@/en/learn-and-explore/article/ftlzi4po/af-area-modes.html  it's mentioned as only possible when using multiple AF points

That also is accordingly mentioned in this article (although it talks about 3D focus tracking) http://www.nikonusa.com/en/Learn-And-Explore/Article/ftlzi4lx/3D-Focus-Tracking.html#@/en/learn-and-explore/article/ftlzi4lx/3d-focus-tracking.html the AF system must accumulate subject location data using multiple focus areas

So it seems to be physically impossible to have AF tracking/predictive focusing (or however you might want to call the option of the camera focusing on a subject on a spot other then where it actually is in that moment, in anticipation on where it's expected to be the next moment) in AF-S.
Simply because you then only use one AF point, which, at the moment the release button is pushed in halfway, is busy achieving a 'sharp picture' at the spot where the one AF point is aimed at, and there simply are no other AF point available to calculate where the subject is expected to be the next moment.

This (only one AF point active when using AF-S mode) is also stated in this article (not an official Nikon site, but a Nikon user site) https://blog.nikonians.org/digitaldarrell/2011/08/dd-understanding-nikons-autofocus-af-area-and-release-modes.html

Or I'm a misreading the articles mentioned?

[Matthew Currie]

Well, I really did my best but I didn't find any mentioning on the several Nikon tech sites of predictive AF possible with AF-S

In this article http://www.nikon.com/about/technology/rd/core/software/caf/index.htm , it is only mentioned in combination with AF-C, just like in this article http://www.nikonusa.com/en/learn-and-explore/article/ftlzi4pn/51-point-autofocus-system.html#@/en/learn-and-explore/article/ftlzi4po/af-area-modes.html  it's mentioned as only possible when using multiple AF points

That also is accordingly mentioned in this article (although it talks about 3D focus tracking) http://www.nikonusa.com/en/Learn-And-Explore/Article/ftlzi4lx/3D-Focus-Tracking.html#@/en/learn-and-explore/article/ftlzi4lx/3d-focus-tracking.html the AF system must accumulate subject location data using multiple focus areas

So it seems to be physically impossible to have AF tracking/predictive focusing (or however you might want to call the option of the camera focusing on a subject on a spot other then where it actually is in that moment, in anticipation on where it's expected to be the next moment) in AF-S.
Simply because you then only use one AF point, which, at the moment the release button is pushed in halfway, is busy achieving a 'sharp picture' at the spot where the one AF point is aimed at, and there simply are no other AF point available to calculate where the subject is expected to be the next moment.

This (only one AF point active when using AF-S mode) is also stated in this article (not an official Nikon site, but a Nikon user site) https://blog.nikonians.org/digitaldarrell/2011/08/dd-understanding-nikons-autofocus-af-area-and-release-modes.html

Or I'm a misreading the articles mentioned?

No, I believe you are reading the articles right with one small exception.  As far as I know, there is no attempt to make AFS anything more than single one-shot focusing without prediction or adjustment after the initial hit. 

The small exception is that, on some cameras at least, it is possible to combine AFS with multi-area focus mode, in which the camera's processor chooses the focus point or points.  However, in AFS this is still a single-shot event, and once focus is achieved,  it does not change again.

e.t.a.  for example, on the D3200, in AFS one can choose between single point and MA modes, but cannot choose dynamic area or 3D.

In AFC mode, the camera does not seem able to distinguish between camera movement and subject movement, which is why one cannot focus and recompose in AFC.  I would assume that this is the case in AFS as well, and thus, it would be impossible to allow for adjustment to a moving subject without disabling the ability to recompose.

[Erik Lund]

I'm not preaching anyone to use AF-S mode for moving objects. You are free to do what ever you like

BTW: Again I'm not stating there is any tracking going on in AF-S!

I switch between the two modes all the time and really like them both and find that they both are working amazingly good.

I have almost no out of focus images for AF-S mode for moving subjects,,, 

Yes if I half press and hesitate to fully press then I get an unsharp image if DOF is shallow, but that is misusing the AF-S mode,,, in that case I switch to AF-C or the AF-On

BTW I'm referring to F4, F5, D1, D1X, D2X, D3, D3X and D810 it has just gotten better and better

Lenses - Prediction:

Below is a description for inspection and adjustment of an AF lens focusing system:

In both cases, AF-S or C the camera use the information from the CPU  about 'prediction' of how to drive the AF motor of the particular lens in use to reach the right focus plane at the right time, to achieve a sharp image.

Here is the Nikon Service manual for 24-70mm AFS 2.8:

http://allphotolenses.com/public/files/pdfs/4b4fb97547c5d54819491c07c715f2c2.pdf

On page 70 and forward you see how to inspect and adjust a lens CPU AF values.

On page 76-79 it is described how the 'predictive' part of the lens focusing, overrun/underun is measured and adjusted.

This show that the camera is also predicting or taking an educated guess, from the values given by the lens CPU how to run the AF engine inside the lens so it stops focusing at the right point in time.

The camera is not just picking up the movement and position of the object with the AF sensors in AF-C or AF-S mode and just fire the shutter, it would miss the focus point.

PS no Bjørn cant program this into your CPU for you Manual Focus lenses,,,

[ArendV]

Erik, you know much more about lens technology than probably anybody on this forum but this technical manual does not convince me that in AF-S mode prediction is happening. The overrun/underrun part is on on the lens acquiring focus quickly in back-and forth driving to get to the final position and does not cover prediction.

I would only "push through" without checking focus acquisition in "emergency situations". Normal operation for me in AF-S is to half press to confirm focus and then without hesitation :-) push to actual exposure.

[paul_k]

BTW I'm referring to F4, F5, D1, D1X, D2X, D3, D3X and D810 it has just gotten better and better

That I fully agree with

My first AF body was the F801 (skipping the F501 was intentional, the AF on that body really was slow), and upgraded with each new AF body that came after it (F801S, F90, F90X), simply because for what I shot (catwalk and fashion on location) I really needed a faster AF (although that didn't stop me from still shooting catwalk with a 4.5/300mm ED, manual focus, or location shoots with a 500mm mirror reflex)

In my experience up to, and including the F100, dynamic AF wasn't 100% reliable (went flat on my face with a shoot when I relied on it with the F100, never liked that camera since  )

Fortunately it became near foolproof on the D1 and upwards, and I don't hesitate to use it nowadays (though never 3D AF nor Auto Area AF)

[charlie]

Erik, you know much more about lens technology than probably anybody on this forum but this technical manual does not convince me that in AF-S mode prediction is happening.

If the camera is set to AF-S/focus priority and the photographer fully presses the shutter button to take a picture there is a very small lapse in time between the moment the camera acquires focus and the moment the image is recorded. Compensating for that lapse in time, however small it might be, is what I believe Erik is speaking of and it seems reasonable to think that it would be programmed that way seeings how the technology is already there.

Seems a few tests on fast moving subjects could verify this.

[simsurace]

Erik, you know much more about lens technology than probably anybody on this forum but this technical manual does not convince me that in AF-S mode prediction is happening. The overrun/underrun part is on on the lens acquiring focus quickly in back-and forth driving to get to the final position and does not cover prediction.

I would only "push through" without checking focus acquisition in "emergency situations". Normal operation for me in AF-S is to half press to confirm focus and then without hesitation :-) push to actual exposure.

Without being able to peek into the code of the AF system, some sort of prediction (in the sense of estimation) is needed to deal with the data coming from the AF sensors, which is incomplete and noisy.

When the AF sensor picks up a signal, that is not an exact measurement as there is uncertainty about where exactly the subject is. Movement of the subject increases uncertainty about its position, but also means that any delay in the shutter release will change the position. Therefore, I presume, it would have been impossible to get this system to work reliably without incorporating prediction also in AF-S mode. If you half press in AF-S with a moving subject, the system will inevitably fail.

[ArendV]

Full pressing in AF-S mode without checking focus acquisition will result in a high number of failures in my experience and therefore I consider it a bad practice only to be used in emergencies.
To me movement prediction should not be part of the AF-S algorithm and I have not seen any convincing evidence in this thread that it actually is, but I will rest my case.

[Erik Lund]

Arend, I would not use AF-S the way you describe it.

I regard Marianne Oelund as one who has the a huge amount of knowledge about Nikon AF and AF sensors.

Anyway this is her statement cut out of a long series regarding AF sensor modules

https://www.dpreview.com/forums/post/54762863 and https://www.dpreview.com/forums/post/54211961

Keep in mind that Nikon state that even in Single AF mode, the camera is supposed to be able to detect subject movement, which requires continuing to monitor the AF sensor data until focus is locked.

And:

The AF system designer cannot assume that the subject is stationary in any case. The only way to ensure the lens is moving toward correct focus, allowing for a moving subject, is to recompute focus error as the lens slews. Even in Single AF mode, Nikon claim the system will detect subject motion.