When do you use all of your autofocus points?

Discussion in 'Beyond the Basics' started by gl600, Dec 24, 2009.

  1. gl600

    gl600 TPF Noob!

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    Why is 51 points of AF better than, lets say, 9?
    For 99% of my shots I use one AF point, get the focus locked, recompose then shoot. Is it any better to change AF points to where you want to focus in the frame?
     
  2. Derrel

    Derrel Mr. Rain Cloud

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    Multiple autofocusing points allow the camera to accept and input data from *multiple points* across the frame. If you have a Nikon body with the Scene Recognition System, that system uses color information (RGB color analysis) and distance information to "identify" the original subject and to follow that subject as it moves across the frame, it would be a good idea to learn how to use a grouped AF point focusing strategy for some situations. The multi-point AF focusing concept is one of the advantages of using one of the newer Nikon bodies that have color-aware and distance-aware light metering. If you had a car with five gears, would you ALWAYS use it in 3rd gear? Probably not.

    Your question: is it better to change your AF points where you want the focus in the frame? is a good one; that is one way the Nikon SRS knows what target to follow across the frame; the initial lock-on,as determined by the photographer, is the way the camera knows what the original subject is; you use the multi-controller to rapidly SELECT an AF area, and then the SRS system reads the RGB values, reflectance values, and distance information,and then it can track that subject as it moves across the frame. So, yes, there is a well-known method and a known reason for the shooter selecting his/her preferred intial focusing point(s) underlying the 51-point AF system Nikon has developed.

    Using just a single,center AF point in effect, is throwing away much of the capability of the autofocusing system. An AF system that can collect data from multiple locations around the frame will, if it's a newer Nikon body, be able to do better focus tracking than using *just ONE* AF location.

    On the professional-level Nikon AF systems, people who encounter a lot of difficult autofocusing situations will tell you that they rely upon a multi-point AF configuration for a number of specific scenarios where using only one AF point does not produce the results they want. I would suggest some of the very comprehensive guide books, like the Thom Hogan Complete Guide to the Nikon _______ series as a way to learn more about how to use a modern, complex AF system. AF systems have become very sophisticated,and they require both understanding of the concepts AND practice to master.
     
    Last edited: Dec 24, 2009
  3. gl600

    gl600 TPF Noob!

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    Thanks!
     
  4. Garbz

    Garbz No longer a newbie, moving up!

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    Do you really just use the centre AF point? I know even older cameras like the D200 with it's 11 point AF have options where you select 1 AF point, however the surrounding points are used to assess the image and assist in accurate autofocus and tracking. On this camera there's 4 different options on a selector switch on the camera, and other 4 or 5 options to customise these points, and all in all only 1 set of options will truly give you simple single point AF.

    Even if you don't intend to use the 51 points they improve the AF performance of the camera. But evenutally you'll get into a situation like:

    - Macro photography where the camera is on a tripod, the chance of error is large, and the subject doesn't quite line up with one of the 9AF points of a cheaper camera.
    - Sports where using 51 AF points to dynamically track the ball as it's moving across the field is a godsend.
    - Portraits, because some people just outright don't like focusing then recomposing. The people with 85mm f/1.2s would be the culprits here.
     
  5. KmH

    KmH Helping photographers learn to fish Supporting Member

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    I believe the OP is contemplating getting either a D90 (9 focus points, 1 cross-type point, Multi-CAM 1000 autofocus module) or a D300 (15 cross-type focus points, Multi-CAM 3500DX autofocus module) so they can shoot weddings.
     
  6. Aritay

    Aritay TPF Noob!

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    Good question.

    What if nothing in the pic is moving. Then isn't just using the one point, pushing the shutter half-way down, then re-composing just as good??

    (I do understand if things are moving. But otherwise, isn't it just as easy (easier) to use a centerpoint??)
     
  7. IgsEMT

    IgsEMT No longer a newbie, moving up!

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    I use one center point, lock the focus and recompose.
     
  8. gl600

    gl600 TPF Noob!

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    What I mean t was not to completely disable the other AF points, rather to just select one AF point as the area that the camera will always focus to and then simply recompose. Again, if I am shooting in a studio, a wedding, a landscape (anything besides sports or fast paced wildlife) why would I select all of my AF points to be active?
     
  9. feRRari4756

    feRRari4756 TPF Noob!

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    hey guy i was just reading this thread and was curious about this also. I have a Canon 30d and will be using my 70-200 f4 USM L or 17-55 2.8 IS USM to shoot surfing from the water (with a waterproof housing). What points and AF mode (one shot, servo, etc) do you guys reccomend i should use because the will be coming at me at about a 45 degree angle. You guys might have answered it already but i dont quite understand.

    thanks!
     
  10. Josh66

    Josh66 Been spending a lot of time on here!

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  11. keith foster

    keith foster TPF Noob!

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    Thanks O! That was a good read and good to know stuff.
     
  12. Garbz

    Garbz No longer a newbie, moving up!

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    Jeep hit the nail on the head in the above post. The parallax error when shifting the lens will shift the focus point. Now let me just say if you're in a studio and nuking your subject with light so you can use your wide lens at f/16 then realistically this will make no difference to you at all.

    But focus and recompose simply does not work when you're shooting at f/1.4. You will have a high failure rate simple because of the hair thin depth of field. Same for macro photography.

    Even in the studio the focus points are simply there to give you options. You'll ultimately find the points in the centre are the most accurate and reliable, but sometimes they are just not suited for the job.
     

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