S-AF, C-AF, and C-AF+TRacking

Discussion in 'Olympus Cameras' started by Clint, Nov 3, 2013.

  1. Clint

    Clint Mu-43 Hall of Famer Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    There seems to be some confusion and miscommunications about S-AF, C-AF and C-AF TRacking modes. Partly because Olympus has changed the concepts from the 4/3 to the m4/3s cameras. Let's see if we can put this in a big nutshell.

    S-AF - Locks focus once and stays there. Good for stationary subjects or locking focusing and reframing. Because of the speed of the S-AF you can also lock focus just before your intended moment and then relock focus as you capture the moment want to capture. Anticipation of the moment is everything when focusing by this method.

    C-AF - The camera continuously refocuses locking onto whatever you have under the selected AF target. If the subject moves and the camera does not, the camera will lock focus on whatever it sees under your selected AF target. If something moves between you and the subject the camera may very well lock onto the moving item. For C-AF it is important to keep your AF Target on your subject!

    C-AF+TR - Locks focus on the subject under the selected AF target. If the subject moves the camera will try to follow the subject and keep refocusing on it, as long as you keep the subject within the viewfinder and fairly close to your selected AF Target. This provides you some leeway in not having to keep your explicit AF Target on the subject. C-AF+TR is ideally intended for where your subjects move quickly in unexpected directions. If you can anticpate and follow your subjects then S-AF or C-AF are better focusing modes for use.

    C-AF and C_AF+Tracking can be interrupted by something passing between you and the subject, in which case the camera may (probably will) lock focus on the something passing between you and the subject, unless you have something other than Off set for C-AF lock.

    C-AF lock - determines how long the camera should try and stay focused on the item under the AF Target of your choice, if something was to interfere with the initial lock. Since C-AF lock is set to Off by default, the camera will jump to anything it perceives you want to focus on.

    So if something moves between you and your intended subject, and if the camera captures that in one of the continuous focus moments, the camera will refocus on that new target. You can negate the speed with which C-AF and C-AF+TR jumps to new targets by setting C-AF Lock to Low, Normal, and High.

    I have played very little with m4/3s lens, C-AF and C-AF Tracking but was very disappointed when trying to use 4/3 lenses on the E-M1. I can say with 4/3s lenses you want to pick the highest contrast vertical element you can lock onto with good light. High contrast lighting does not help.

    It seemed as if at the C-AF Low setting the focus would change to a new subject slower than with C-AF lock set OFF, and as I moved to Normal and then High settings the camera would tolerate longer periods before changing to a new subject. But I had so many issues with the camera locking focus with the 4/3s lenses I am not 100% sure of this.

    I can tell you a great place to practice is a carousel or a busy highway. Start from further away and then move closer. Your positive or negative experince with C-AF and C-AF+TR will greatly be influenced by your level of experince.

    We also need to consider Release priority as it partly determines how well C-AF shots turn out.

    If the camera is set to Rls Priority (Custom Menu C) Off, then the camera must have locked focus before allowing the shutter to fire. Which initially sound sensible, but can be extremely irritating!

    If Rls Priority is set to ON, then the shutter can be released before the camera has locked focus. The premise here is that the camera focuses so quickly and/or the camera is already in the process of locking focus that between the time you press the shutter button and the shutter fires - focus will be locked!

    You can have different Release Priority settings for S-AF and C-AF. By default Release Priority for S-AF is set Off and for C-AF it is set to On.
    • Like Like x 18
  2. hazwing

    hazwing Mu-43 Hall of Famer

    Nov 25, 2012
    useful article
  3. GreenGhost

    GreenGhost Mu-43 Regular

    Nov 30, 2012
    Peter Liakopoulos
    Thanks Clint that has made things much clearer for me. Resolved some misconceptions/misunderstandings.

    Sent from my iPad using Mu-43 mobile app
  4. hkpzee

    hkpzee Mu-43 All-Pro

    Sep 5, 2011
    Hong Kong
    Thanks for taking time to lay these all out, Clint!

    I am currently still trying to test out the various C-AF Lock settings on different type of targets. I just wish Olympus would provide a better explanation of what they consider Low, Normal, and High, and I can deploy the correct C-AF Lock accordingly. Having to dive deep into the menu to change the C-AF Lock setting every time makes it difficult to compare the various settings on similar targets or situations...
  5. M4/3

    M4/3 Mu-43 Top Veteran

    Sep 24, 2011
    How does all that work when shooting video? On my E-M5 when I shoot video in Aperture Priority mode using S-AF, the camera does "not lock focus once and stays there" but continually adjusts focus, often focusing on the background instead of the subject in the foreground that I'm aiming the green focus box on. Even when I configure the smallest focus box possible. And even occassionally when shooting stills. Same thing happens when using my E-PL1. So perhaps there is something fundamental I don't understand about how to use the focus box to achieve focus.
  6. Clint

    Clint Mu-43 Hall of Famer Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    I do not think we'll be hearing any specifics about the C-AF lock options. First because no other manufacturer has relayed detailed information about their lock options and second because of the number of variables involved.

    That is why I mentioned the great places to practice. I needed places to proactive that I didn't have to wait for events to occur. With my earlier Olympus 4/3s and Nikons I finally figured out some base guidelines I could use and adjust quickly to the situation. Each camera is different and each situation is different, so practice makes the difference.
  7. Clint

    Clint Mu-43 Hall of Famer Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    I don't shoot video much more than 30 second clips using manual focsu so I can't be of much help.

    Have you tried setting the AEL/AFL to lock focus? Once done you may also have to hold the button to keep focus locked, and when you release the button it tells the camera to focus. Just a SWAG (scientific wild ass guess).
  8. New Daddy

    New Daddy Mu-43 Regular

    Jan 24, 2011
    I don't have an Olympus but Pannys behave the same way. According to the manual, AF-S is ignored and everything works as AF-C in the movie mode. Even with a non-AFC lens on (e.g., 20mm f/1.7), the camera will hunt for focus continuously, which is a pain with the loud focus motor noise of 20mm. One way to overcome is to switch to MF once you have focus lock if the subject is stationary.
  9. Bots' Revenge

    Bots' Revenge New to Mu-43

    Nov 1, 2013
    I have found that using Continuous focus with Release priority set to OFF produces the best result (in comparison to RLS priority set to ON) because the camera keeps constantly switching the focus plane back and forth and when I hold the shutter button the camera takes a shot only when there's focus on the subject. If I keep the release priority to ON I may press the shutter button at will and it's a matter of luck to have proper focus.

    This matters to me a lot when I'm going to shoot a bride and groom walking towards me during their ceremony. I need to know that when I press the shutter button the camera will take a shot when there's actually focus on them. I have no need for a shot without focus.
  10. New Daddy

    New Daddy Mu-43 Regular

    Jan 24, 2011
    Yes, the Release Priority makes a lot of sense.
    But if you have it on, how is the whole AF-C + release priority different from AF-S + rapid succession of taking single shots? For sports, your finger will tire from rapid shutter releases, so you'd definitely need AF-C + Release priority + Burst. But for more moderately-paced activities, like wedding, were you'd also want to take some time to compose between shots, wouldn't multiple AF-S shots work better? This is not a rhetorical question. It's a real question asking about people's experience.
  11. Halaking

    Halaking Mu-43 Top Veteran

    Dec 17, 2012
    Los Angeles
    If you using 12-50mm or the new 12-40mm lens to shoot a movie, there is L function bottom on the lens, once you push the L bottom and hold, it actually stop focusing in C-AF mode, you can prevent the C-AF keep hunting once you already get the focus, release the L bottom when your target move, and let the C-AF work again.
    • Like Like x 1
  12. Bots' Revenge

    Bots' Revenge New to Mu-43

    Nov 1, 2013
    It's a good question. The way I see it - when using AF-S and for example a wedding couple is walking towards you it takes some time between achieving focus and actually pressing the shutter button. During this time the people would move even closer and slightly out of focus. On the other hand AF-C takes a shot immediately after it finds focus - no delay. It's constantly hunting and doesn't take a shot without focus. We people can't react as fast as the machine by itself.
  13. Yohan Pamudji

    Yohan Pamudji Mu-43 Veteran

    Jun 21, 2012
    Mississippi, USA
    Some examples of situations where AF-C would be desirable: bride and father walking up the aisle, bride and groom walking down the aisle, bride and groom making entrance or exit at reception, etc. AF-S would be pretty dodgy for those situations and these are "high value targets" if you will--you don't want to not have usable shots from these set pieces.
  14. napilopez

    napilopez Contributing Editor

    Feb 21, 2012
    NYC Area
    Napier Lopez
    From my understanding, it seems most wedding photographers prefer to just use S-AF even on DSLRs with good tracking, myself included, but I would love to have good continuous autofocus for precisely the moments you mention. With AF-S, you need to be really good about quickly refocusing(which might not be fast enough, particularly if it's a fun shoot where the couple wants to run), or prefocus in which case you might actually miss the decisive moment if it doesn't happen in your selected focal plane.
  15. HappyFish

    HappyFish Mu-43 Top Veteran

    Sep 8, 2012
    I use S-AF once they are the first shot the rest are not adjusting far to many issues with C-AF even on FF gear I never use C-AF most my buddies don't either ? a few do not sure the actual numbers :) 

    its more mash it down let it focus and grab the shot often its waiting for the couple to look at each other etc.. those moments she raises her flowers and such you want so its not just a put it on take the shots you will get one you are trying to get a shot ?

    wanting to try manual with peaking next wedding though for fun :) 
  16. Clint

    Clint Mu-43 Hall of Famer Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    I disagree with this, I've used AF-S on both 4/3s and u4/3s shooting jet aircraft, race cars, runners and more with great reults. And I often will turn off release priority for AF-S with great results.
  17. photo_owl

    photo_owl Mu-43 Regular

    Nov 8, 2013
    one small thing for those that don't read manuals..... C-AF doesn't operate normally in H sequential release mode; once you take the first frame focus is locked in that plane.
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  18. New Daddy

    New Daddy Mu-43 Regular

    Jan 24, 2011
    Which body are we talking about?
  19. Clint

    Clint Mu-43 Hall of Famer Subscribing Member

    Apr 22, 2013
    San Diego area, CA
    Just a little bit ago I read this in the manuals-

    E-M5, Page 53
    E-M1, Page 55

    Sequential H
    Focus,exposure, and white balance are fixed at the values for the first shot in each series ([S-AF], [MF]).

    Sequential L
    Focus and exposure are fixed according to the options selected for
    [AF Mode] (P. 86) and [AEL/AFL] (P. 86).

    So I'm thinking C-AF would be the mode to use for low or high speed sequnces. I'm headed out the door shortly to check this and few other things I had on my list for the E-M1 today.
    • Like Like x 1
  20. theanser

    theanser Mu-43 Regular

    May 31, 2013
    Dear Clint,

    Can I ask what type of focus point works best for the C-AF? is it the smallest single focus point. Its my methodology right that to get my C-AF work, I half press my shutter and point my focus point on the subject and follow the subject movement so that it stays inside my focus point and fired burst?

    Thanks a lot !
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