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Thread: center focus point or selective focus point ?

  1. #1

    center focus point or selective focus point ?



    I am a bit confused & reluctant on which one to use for the sole purpose of achieving tack sharp photos. I know it's definitely affected by shutter speed ( handhold-ability) & focus point selection. I have tried using a tripod/mirror lockup/remote shutter release method, which of course, achieves the "bitingly" sharp outputs. However, as I try to refine & hone my skills in focusing, be it manual/auto, some pics tend to be out of focus when using focus & recompose. There's a different story with choosing the outer focus points closest to the subject. This technique produces a much sharper outcome compared to "focus & recompose". So, what's the best advice to take tack sharp photos? I agree that some lenses tend to be soft at different apertures & focal lengths (zoom lens).


    Which is the best technique IYHO?[]

  2. #2
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    Re: center focus point or selective focus point ?



    Focus and recompose is a technique created by point and shoot users. It is not an effective technique for dslr users. The pictures will turn out as you are saying, sometimes focus will be fine, sometimes there will be a slight adjustment and focus will be off. always try to use a focus point. Compose your shots based on the focus point chosen and your subject. That is why the higher end / more expensive dslr's have more focus points. You may have to go some cropping afterwards, but at least you will have great focus which will give you more latitude to crop.

  3. #3
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    Re: center focus point or selective focus point ?



    Well, selecting a focus point to cover your subject is the "proper" technique. Focus and Recompose will always throw your subject out of focus, unless you have enough depth of field to make up for the shift in the focus plane you are introducing.


    The problem is that focus points tend to stay away from the perimeter of the frame (especially on full-frame), this is due to the fundamental design of our SLR's mirror box. The secondary mirror has to get enough of a down-angle in order to reflect light down into the focus sensors, that means it must be smaller (and attach lower on the primary mirror) to avoid hitting the sensor/film-plane. Now, this really only affects top-bottom, so I guess it would be possible to go left-right to the edges, but they don't AFAIK.


    So what to do? I would rate the various methods I am aware of from best to worst like this:


    1. If using a tripod is an option, (i.e. for a landscape or static scene) I would recommend using live-view, and moving the little zoom box to hone-in on your subject, then manual focus using the zoomed-in view.


    2. If you can reach the subject with a focus point, select that focus point, then focus.


    3. If you must use focus & recompose (for speed), try to increase depth of field, or just be aware that you are moving the focus plane, and try to compensate somehow. (move the camera or slightly or move the focus ring, although this is probably as risky as not trying to compensate at all!)


    Finally, remember you need a lens that is sharp in the corners if you will be putting a subject there. If your lens is only sharp in the center, you are better off always centering your subject, then cropping to suit composition, provided you have the resolution. Also remember the outside focus points vary in quality depending on the body. Your best focus points are usually in the center.


    IMHO






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    Re: center focus point or selective focus point ?



    Focus and Recompose is perfectly fine on DSLR, as long as you don't change the distant between you and the subject. Of course to get optimum result you should select other focus points instead of the center one.

  5. #5
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    Re: center focus point or selective focus point ?



    Quote Originally Posted by Sinh Nhut Nguyen


    Focus and Recompose is perfectly fine on DSLR, as long as you don't change the distant between you and the subject. Of course to get optimum result you should select other focus points instead of the center one.



    Just be careful, wide angle lenses are less forgiving on recomposition. Longer than 50mm you will probably be okay and 100 on you will be fine.

  6. #6
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    Re: center focus point or selective focus point ?



    Keith is right about wide angle lens!

  7. #7
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    Re: center focus point or selective focus point ?



    what the smart guys said.


    Focus and recompose is fine in telephoto settings, where the focal plane doesn't change much with distance. Wide angle, it's completely pointless, and downright wrong.


    I try to use the nearestfocus point if I have time to dink with it, when not in a telephoto situation. Otherwise, if the center point just performs better in difficult to focus situations, i'll just use it, not recompose, go a little wide, (by leg or zoom) and then crop to get the framing I want.


    I don't have any cameras with live view, so I unfortunately don't have that option, but that, combined with an aperture preview, would be most ideal, but often impossible with things (or light) that moves.

  8. #8

    Re: center focus point or selective focus point ?



    Well, I do feel that the nearest focus point selection is the best technique based on most of your inputs. I'll definitely practice more on this technique. I'll probably use center focus point selection when shooting moving subjects in the AI-Servo Mode. BTW, thanks for all those suggestions! I'll definitely be a happier shooter with this knowledge that has been provided!

  9. #9
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    Re: center focus point or selective focus point ?



    From watching some people in class, a few people have a nasty habit of moving their camera forward when recomposing. Me, along with many others never have any trouble center focusing then recomposing... just something you have to get used to.

    I guess it comes down to how much time you have to focus andwhetheror not you are using a tripod. When using a tripod, it only makes sense to manual focus or selective focus point.

  10. #10

    Re: center focus point or selective focus point ?



    Focus and recompose doesn't work with the 85mm 1.2L II at f2 most of the time and never works at f1.2. I used to be a focus and recompose guy until I got that lens. The DOF is so shallow at 10' that it will throw the subject out of focus by focus and recomposing. All my shots in portrait layout are taken with the top most point and then I'll crop out all the extra space. I hatewasting pixels I know i'm going to crop outbut at least the shots are in focus.

    Fred~

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