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Best focusing method for stationary and moving people

saqibzulsaqibzul Member
edited October 2012 in wedding photography
I am having to re-think my focusing strategy. I have been used to focus center and re-compose. Perfect for landscapes, and for weddings that seems to be fine when the subject is stationary and you have a lot of time to do this. A lot of time in the sense, if you miss, you can do another attempt to nail it. But in situations where the subjects are moving and you want eyes to be always in focus and not be dead center too, how do you do it.
I have recently configured my camera to do both continuous and focus center by pushing the AE button and release method. But using the center point does not guarantee the compositions you are looking for. I know you can move focus point around, but during weddings where there is a lot of action happening quickly, missing a perfect moment due to bad focus can be an undesired result.
On the same token, using auto focus with auto points can be ok with you cannot absolutely guarantee what got focused was what you wanted.
Any best practices or technique from you established pros would be highly appreciated.

Thanks,
Saqib

Comments

  • i dont know of any professional photographer that uses auto focus with auto points, its too unreliable and slow in my opinion, i use back button continuos single point 90% of the time somtimes switching over to single
  • TrevTrev Moderator
    edited September 2012
    Agree with Naftoli, but around 25% continuous [bride in aisle and reception] and 75% single shot, with a few continuous with bride/groom walking/running in location shooting when necessary.

    I do try to use center point when I can, and recompose, but only if f4 and up so I don't alter plane of sensor too much. f3.5-f1.4 I use outer points, so I am not moving my camera or only a tiny bit.
  • Naftoli,
    Thanks for your response. With your continuous single approach, how do
    1. Compose images where eyes are not in center.
    2. Avoid blurry images as a result of camera shake. Asking since with this approach assumption is you are doing burst shots. Ok for fast shutter speed, but how do you manage in low light environment?

    Thanks for your help
  • i use back button focus all the time, when the eyes r not in the center (which is usually the case) i focus and then compose.

    As far as avoiding getting blurry images due to camera shake u have to know urself and ur camera as too how slow of a shutterspeed u can go to many times when taking semi candids with on camera flash i first take a shot at a safe speed like 1/80 to 1/125, and then quickly roll the shutterspeed dial down to somthing like 1/40 to allow more ambient to light up the background, this way i have the safe shot without a chance of blur and if the second shot comes out nice then i can delete the first one(of course it helps to have an expensive FX body that can easily do iso 6400 which i dont and super fast 2.8 lenses)
  • Also, at shallow depth of fields, f2.8 or wider, focus and recompose actually changes the plane of focus. For example, you focused on an eye, and then you recomposed, and then find that eye is not as sharp.

    http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm

    This doesn't mean that focus and recompose is always a bad technique, but you do have to be mindful of your depth of field and what you are focusing on.
  • Stephen, I am not sure if I totally buy into the article's claim. Being a shooter from the manual focus era, I would always manually focus for the eyes and re-compose. The lens had distance meters on them for the very same reason, and were also used for calculating hyper-focal distances. As for the claim that everything parallel to the camera sensor regardless of its distance from the center of focus is equally in focus is new information for me. Using this analogy, once can say if I shoot a 1000 foot wall, which happens to be straight and parallel to the camera; setting the focus in the center , the whole wall will be equally in focus from end to end.
    If you can point me to more scientific sources that justify this claim with workarounds to avoid this, that would be great. Based on the above info, I would prefer to be able to dynamically change my focus point. I have seen the focus point can be moved on canon, but will have to go through the manual for nikons.

    Saqib
  • StephenStephen Member
    edited September 2012
    Saqib,
    Here is an article with the mathematics of what happens during focus and recompose.
    http://www.mhohner.de/essays/recompose.php

    Comment #7 might explain why you never had an issue with focus and recompose with manual focus.
  • Hi Stephen,
    Thank you for taking the time to do the research. I have to say, I am still not a believer yet. I understand the trigonometry he is trying to use present this theory on focal planes shifts and things becoming out of focus. Shooting at f1.4, focusing eyes, and then re-composing you should never get eyes sharply in focus, yet we tend to get them, minus edge softness and camera shake etc. As for his claim on comment#7, that with manual focus you compose first and focus later and therefore dont see the problem, Having used canon FD lenses for many many years, I can tell you, it ain't true. Mainly because the lens focus area was in the center; unless you always compose first and then focused for people's belly buttons instead of the eyes.
    I can be lenient enough to believe that the complex software algorithms (aka autofocus, 3d, auto point, multi-point etc.) which attempt to make focusing life easier for consumers is propriety software, could there be bug in a specific vendor's firmware, very much possible. Is it the intended functionality to have your camera back focus for a simple scenario of focusing on one point and then changing your composition without changing the distance from the main subject, If I was Nikon/Canon, absolutely not! I did a couple of shots with my nikkor 1.8 at f1.8 to try to re-produce the claim, but could not. So as far as I am concerned, all this more of a conspiracy theory without any validation from nikon or canon, and I encourage you go and do the same if you have an f1.4/f1.2 lens.

    P.S. I still haven't figured out how to have perfect compositions using the BBF button in continuous focus mode (center point), unless I shoot wide and crop in post.

    Saqib

  • StephenStephen Member
    edited September 2012
    Saqib,
    Perhaps your definition of sharpness and the author's claim of sharpness are not the same. I cannot dispute the math of the focus shift in that equation; math is absolute. As to how that focus shift translates into image sharpness, that is not as clear cut.

    You and a number of manual focus shooters claim otherwise, so it's possible the math is not addressing the proper problem. If you say the image is "reasonably sharp" at 100% view using focus and recompose, I'll have to take your word for it.

    I do not have a f1.4/f1.2 lens to test this even empirically, nor would I do so. This would require a rigorous test using control environments (cameras stable on tripods, repeated tests, etc.) and an objective evaluation of sharpness.
  • correct me if i am wrong but the focus and recompose (back focus) issue only makes a difference when the subject is close to the camera ie: with a wide lens. however with a wide lens u generally have a large dof so the small shift of the plane of focus doesnt have a noticable effect on subject sharpness. conversely when using long glass and the subject is further away from the camera the diference in distance from the plane of focus is so minute that there is virtually no difference than if u had not recomposed, hope this makes sense
  • TrevTrev Moderator
    It also depends on the natural depth of field with your choice of aperture. The wider the aperture, [f3.5 - f1.4] the more chance of focusing error, and as Naftoli says, the closer to subject the more chance.

    I have found the greater error is on the vertical/portrait axis shift [ie: up/down] and not so much on the horizontal placement [sideways] that the error occurs.

    This may be just me [no evidence to support my theory] but I also think there is a greater shift on focus/recompose on the vertical axis naturally occurring when moving camera up and down as opposed sideways, and not only that, but it also depends on the actual camera orientation, in portrait or landscape position and how you hold it.

    It just seems logical if you think about it, since the portrait orientation you have a tendency to move more.

    Only a theory of course.

  • Saqib,
    The math approach is very similar, but Bob's example does properly follow up on the math, i.e. the math says focus shift happens, but is it noticeable in reality? Not really.

    So, I'm correct that focus shift does happen. But, you're correct that this shift doesn't have much significance for the photos we take, since the shift values are very small.

    Math is absolute, but you always need someone to interpret the data, which is what Bob Atkins did. I'm satisfied with in changing my opinion to reflect this.
  • Stephen,
    Yes, I am a believer now in theory, but not in practice. :)

    Saqib
  • im gonna go so far as to say that with a 70-200mm u should be fine at any aperture any focal length and any subject to camera distance. its the 10mm f1.2 lenses u gotta worry about :)
  • One can choose a focus point at composition time using selection pad/dial on both canon and nikon. This should be an easy to do reduce the out of focus issue discussed above. Reading the manual helps :)
  • sazqibzul, of coarse that is also an option however the outer focus points r not as accurate nor as fast as the center focus point, besides it takes additional time to keep moving the focus point around with the multiselector for each shot like if u switch from taking a vertical picture to a horizontal
  • Naftoli, you raised good points. I haven't seen any glaring difference in accuracy and speed using my d7000 (so far). As for moving the focus, I will take that (ifmi can) over risking a soft image.
  • mvheystmvheyst Member
    edited October 2012
    http://www.mhohner.de/essays/recompose.php

    In this picture, you focus on a static object (the flower) A and move (or recompose) the direction of the camera towards B. The camera stays in focus on the blue line, as the distance from the camera towards the blue line stays the same. When your camera focuses at point B, the subject (the flower) is actually at a closer focus distance than before. The difference is indicated by distance "d". The camera's depth of field at point B should be larger than "d" to keep the flower in focus after you recomposed.
    image

    The mathematics to focus and recompose is correct, but:

    A) You need to take the distance from the camera to the subject also into consideration.
    B) The closer the camera get to the subject, the shallower the depth of field becomes.
    C) The picture above assumes the subject to camera distance is static when you recompose.
    D) You need to consider the amount you recompose. The more you recompose, the larger the possible problem.
    E) When the subject moves towards or away from the camera, d changes accordingly.
    F) The faster the subject moves towards or away from you, the larger d may become during the time (e.g 2 seconds) it takes to recompose. You need to take the distance to the object at the same time into consideration. (e.g. Recomposing a flying aircraft vs a person 5 metres away - when both moves towards you, 2 seconds after you initially focused)
    G) An aperture of f/1.4 will give more problems than F/8 when you recompose, because d may be larger than your "depth of field" when using f/1.4 compared to f/8 in the same situation.
    H) You must also remember that "depth of field" is gradual, and you will have "perfect focus" only on a single point (The blue line in the picture above). The further you move away from this point, the more "out of focus" the picture becomes. In practice, you need to be in an "acceptable range" from the 'perfect focus' spot to preceive the image as being sharp, or to get max sharpness.

    If you want your subject to be in focus, your depth of field needs to be larger than "d" to keep the subject in focus when you recompose.

    For this reason I prefer to use the focus points at the sides. I prefer to focus directly on the spot which needs to be sharp.

    Saqib, the best focus method should be practical to use in a given situation, and a single method may not suit all situations you encounter. You have to adjust accordingly.

  • mvheystmvheyst Member
    edited October 2012
    From the above, when you recompose, you have to deal with the following variables, from the time you lock Focus until you release the shutter:

    1. MOVEMENT: Is the subject and / or camera in a static position when you recompose, or are one or both moving when you recompose?

    2. DIRECTION OF MOVEMENT: What is the direction of movement of the camera or subject? Are they moving towards each orther or away from each other?

    3. SPEED: What is the speed of subject or camera movement?

    4. TIME TO RECOMPOSE: How long does it take you to recompose? This is important when you have subject or camera movement.

    5. DISTANCE FROM CAMERA TO SUBJECT: What is your distance to your subject?

    6. APERTURE: What Aperture do you use? (e.g. f/1.4 vs f/11)

    7. THE EXTEND OF THE RECOMPOSITION: The further you recompose with certain settings, the more problems you will encounter.

    8. RECOMPOSE FROM TOP TO BOTTOM vs LEFT TO RIGHT.


    DEPTH OF FIELD: Is your subject still within the "depth of field" area after you recomposed the image? The above points (1-8) may all influence the depth of field when you recompose.
  • Neil vNNeil vN Administrator
    Saqib .. in case you've missed this article:
    http://neilvn.com/tangents/2010/11/06/nikon-d300-d700-d3-d3s-d3x-focusing-modes/

    With the D4 now, I have had to adapt again, because the focusing modes are different than they were on the D3 / D3s.
  • ZenonZenon Member
    edited October 2012
    Same thing mvheyst posted - just different author.

    http://visual-vacations.com/Photography/focus-recompose_sucks.htm

    They moved the DOF preview button to the right side of the 5D3 which is better as can use your pinky/ring finger on the right hand. Better than left. I set custom controls so it will toggle back and forth between One Shot and AI Servo. Only problem is you have to hold it. I wish it just switched w/o holding it. Otherwise I use the Q screen on the back to change. I always use AI Servo when the couple is moving and One Shot when static, never AI focus.

    I used the centre point and recomposed (which I never liked) using my 5D2 and used the outer focus points on my 7D. Now I will use the outer focus points on the 5D3.
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