Do most of you folks find having several AF points helpful or do you find them actually problematic? I am finding that turning them all off, and only having the center AF point active, is the quickest way to get my shot in focus. It seems to me that when I have them all turned on that oftentimes the "other" focal points dominate and concentrate on a part of the subject I could care less about, and in so doing blurring the part of the subject I do care about.
There have been debates regarding 9 AF points vs. 51 AF points, but I am finding only having 1 suits me just fine. I am curious if others feel the same way or if I am just missing something important?
Thanks for any feedback.
Modern AF systems are complex, it is important to learn which combination of AF options to select for the task in hand.
I routinely tweak the AF system for different sports. I never use multiple AF points for portraits and static subjects, unless during action I am tracking someone who comes to an abrupt halt and don't have time to switch the AF system to a single AF point. At closer working distances (e.g.portraits) it is very important to compose the image and then select a single AF sensor to meet the required point of focus (focus on eye), not just use the central AF sensor then recompose the image as the critical point of focus will shift.
Multiple AF sensors used in the right circumstances for unpredictable action photography can be a better solution than relying on one AF sensor. Choosing 9, 21, or 51 AF points is subject and movement dependent. When framing tight on a tennis player (chest up) I will stick to one AF sensor on the face with the normal or long delay lock-on (depends on shooting angle) - I do not want the tennis racket, as it is drawn across the frame, to disturb the AF. If I am framing full length to anticipate a full stretch shot, or player diving for the ball, I will employ 9, or 21 AF sensors as the backgrounds are often plain and will not throw-off the multiple points. With a plain background, 51 3D AF tracking should be perfectly suitable (in theory) when framing full length subjects. Tighter framing where the depth of field is only inches with a 400mm F/2.8, or 600mm F/4 lens at full aperture (even stopped down a little) is a hit and miss affair with multiple AF points, in comparison to an accurately targeted single AF sensor.
No professional sports photographer can guarantee keeping a single AF sensor on an unpredictable moving subject. Should that AF sensor miss the subject momentarily the focus will shift instantaneously beyond the subject. Intelligent multiple sensor AF systems are designed to try and stick with the subject and the reason why Nikon advocate multiple AF sensors to stop the AF wandering to the background (it still fails on occasions). I recently saw a very good image of a rugby player diving straight at camera taken by an accomplished photographer. The photographer was using one AF sensor; the most stunning shot was two frames earlier but the photographer (not AF system) had lost focus onto the background. Fortunately he recovered the situation, although the very best shot escaped him. This is not to say that the multiple AF points would have nailed the subject's face pin sharp as an AF system can only predict!
Nikon's 51 3D Dynamic AF System.A very knowledgeable member of Nikon's (UK) pro team explained this system to me using Pin Art as an analogy -
http://en.wikipedia.org/wiki/Pin_Art Nikon's D3 51 point 3D AF system is using, colour, contrast, and distance data, to track the subject. The 51 AF sensors work in a similar fashion to 51 rangefinder devices, whilst plotting its 3D map using, contrast, colour, and distance data of the subject.
My tests using 51 3D AF tracking with its advanced colour scene recognition technology reveal that it works for some static and slower moving objects, however under certain conditions the system always favours contrast over the initial colour that it was targeted to analyse. In perfect light, photographing kite surfers, the 51 3D AF system would only stay on the kitesurfer's head or torso, momentarily - even with colourful tops, camouflaged patterns and excellent additional contrast from large zips and harnesses. The AF regularly jumped to the white sunlit sea spray created by the kitesurfer's wake, indicating contrast dominance over its colour analysis.
Here is an interesting link from an D3 review by Dr Alex Mustard, an accomplished underwater photographer who initially disliked the 51 3D AF system but then found it very useful for macro work -
http://wetpixel.com/i.php/full/nikon-d3-fi...ific-part-2/P3/Another D3 article, by Dave Black -
http://www.daveblackphotography.com/workshop-at-the-ranch/140-workshop-at-the-ranch-february-2008-the-nikon-d300. He seems to find the D3 and D300's, 51 3D tracking useful. His surfer shot is a typical example where the 51 3D tracking 'may' fair better due to the subject to camera distance (only 70-200mm + 1.4X though) with a more forgiving F7.1 aperture - background wave and other areas in close proximity to surfer. During my kitesurfer 51 3D AF tests I used a 400mm lens with and without a 1.4 converter at F4 - F5.6. Much tighter framed the AF routinely jumped to the strongly sunlit sea spray - very narrow depth of field due to lens choice, aperture and subject to camera distance taxed the 51 3D Af tracking system.
My feeling on the 51 3D tracking is that Hiroshi Takeuchi at Nikon has achieved an amazing technological feat by combining contrast, colour and distance AF calculations -
http://imaging.nikon.com/products/imaging/...19/index_02.htm. However IMHO for faster moving subjects at closer distances using larger aperture telephoto lenses this may require the next generation system with much faster computing power and finer colour data (many more RGB pixels reading the data) to calculate from the subject matter - thats not to say that the current version is not worth employing, it just has its limitations.
Focus tracking with lock-on optionsSetting multiple AF sensors with the focus tracking lock on set to 'off' will defeat the camera's dynamic AF capabilities - multiple AF sensors are designed to work with long, short, or normal settings to keep contact with the subject. If you are using a single AF sensor on a single subject, OFF may be appropriate under some circumstances - if you loose contact with the subject however the AF will instantaneously jump in most cases to the background.
Examples -
Football match where the movement is unpredictable and the subject may only be temporarily blocked -
normal lock-on timer settings - 9 or 21 points, normal lock-on setting.
Cricket match or Baseball game where there is less chance of a player crossing the path of another -
fast lock-on setting enables swifter AF response when changing from one player to another at different locations on the field of play - 9 or 21 AF with fast lock-on.
Runners, as they move along their respective running lanes will often overlap each other in the frame a
long lock-on setting would be more appropriate - 9 or 21 AF points.
The above examples are guides, a particular AF set up carefully considered for a certain type of action can be tripped up by unexpected circumstances. Someone else will swear by other AF methods.
Release or Release + focus priority?Release (CF A1) - enables quick shutter and frame rates.
Release + Focus still provides quick shutter response but will slow down the frame rate to help improve the focus in poor lighting and subjects with lower contrast.
To cap it all I use a singe AF sensor 70% of the time, including action, rarely ever the central one, as it forces sloppy working practices regarding composition; even though the outer AF sensors on the Nikon D3 are not cross sensitive - varying between release and release priority. The remainder of the time I use either 9, or 21, AF points and regularly vary the lock-on, and release options.