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Thread: Advise on focusing

  1. #41

    Default Re: Advise on focusing

    Quote Originally Posted by aspenx View Post
    Let me try to keep this simple.

    "Focus lock" which you are doing now, tells the camera and lens to stop focusing after it is supposedly in focus.

    This means that if your object is 50cm away, the lens will be locked to be sharpest for things that are 50cm away from your lens.
    correction:

    This means that if your object is 50cm away, the lens will be locked to be sharpest for things in a plane 50cm away from your sensor, parallel to sensor..

  2. #42
    Senior Member wildcat's Avatar
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    Default Re: Advise on focusing

    Quote Originally Posted by night86mare View Post
    correction:

    This means that if your object is 50cm away, the lens will be locked to be sharpest for things in a plane 50cm away from your sensor, parallel to sensor..
    At the rate some are getting it and some are not, I am tempted to quote Pythagorean theorem liao

  3. #43
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    Default Re: Advise on focusing

    Quote Originally Posted by night86mare View Post
    correction:

    This means that if your object is 50cm away, the lens will be locked to be sharpest for things in a plane 50cm away from your sensor, parallel to sensor..
    Correct. But will the TS understand? Will it help HIM to solve his problem?

    Then again, i guess it does help for others who might be wondering how exactly it's supposed to work...

    Hope TS manages to figure out with all the new versions anyway. haha.
    Last edited by aspenx; 16th March 2010 at 02:21 AM.

  4. #44

    Default Re: Advise on focusing

    Quote Originally Posted by aspenx View Post
    Correct. But will the TS understand? Will it help HIM to solve his problem?

    Then again, i guess it does help for others who might be wondering how exactly it's supposed to work...

    Hope TS manages to figure out with all the new versions anyway. haha.
    tell him to buy a pack of cards, then take picture of the person with tripod using centre focus, then tell the person

    DAN AH, DAN AH (wait ar, wait ar, in hokkien)

    then hang the card until parallel to his camera back (and thus sensor)..

    then he use centre focus, recompose, and take a second shot, and then move the card again.

    then compare the card location to area of sharpness. confirm will understand after that........... i think..

    but then again, after so long, i'm not so sure already!

  5. #45
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Advise on focusing

    Quote Originally Posted by catchlights
    the best way to confirm it is to do a series of test.

    set up your camera on tripod,
    stick 5 pieces of $10 note on a wall,

    ====++=================
    |.......................................|
    |... $10.................... $10....|
    |.......................................|
    | ...............$10..................|
    |.......................................|
    |... $10.................... $10...|
    |.......................................|
    =======================


    place your camera with tripod aim at the notes on the wall
    with a distance similar your usual distance shooting a portrait
    use center focusing point to focus any $10 note at the four corners,
    once focused, switch to manual focus
    recompose your framing to place the center $10 note at the center
    take a shot

    do a series of test with different aperture, lenses. tell us about your finding.

    nothing beats hand on
    Quote Originally Posted by eltonteo
    Cheam.. will find a time to try it out. Thanks!

    like that also too cheem?? HAR??? really??

    1) Place the notes on the wall as catchlights suggested.
    2) Stand fairly close to the wall (eg. about 1 - 1.5m away)
    3) Mount the 35/1.8, set to A-mode:f/1.8. Use the center-focus of your camera
    4) Aim the camera to the top-right corner note, so that it is in the center of the frame.
    5) Half-press the shutter release till you achieve focus lock (the top-right corner note is SHARP).
    6) whilst holding the button half-pressed, recompose such that the center note is now in the center of the frame.
    7) Fully squeeze the shutter release to take a photo.
    8) Repeat steps 2-7, using different aperture settings (eg. f/2.8, f/4, f/5.6).

    If you have a tripod with a ballhead, that will help you to lock your position better.
    The tripod + ballhead will likely exaggerate the situation we are trying to get you to see, so all the better

    analyze the results. Tell us your conclusions.
    Last edited by ZerocoolAstra; 16th March 2010 at 01:35 PM.
    Exploring! :)

  6. #46
    Senior Member wildcat's Avatar
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    Default Re: Advise on focusing

    ====++=================
    |.......................................|
    |... $2.................... $5....|
    |.......................................|
    | ...............$10..................|
    |.......................................|
    |... $50.................... $100..|
    |.......................................|
    =======================

    Actually like this easier.

    Aim at $10. Distance to $10 is x
    Distance to $2/$5/$50/$100 is root(x squared + y squared) where y is the distance from $10 to $2/$5/$50/$100.

    But x is not root(x squared + y squared) unless y is zero. Therefore, if you focus at $10 distance, but recompose to $2, then $2 will not be sharp, because distance to $2 is now root(x squared + y squared) and neither will $10 be sharp because the focus - previously on the $100, distance of which is root(x squared + y squared) - is now x.

    OK. There. You've forced me to quote the Pythagorean theorem liao.
    Last edited by wildcat; 16th March 2010 at 02:46 PM.

  7. #47
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Advise on focusing

    following on from wildcat's post...:



    Aim at $10. Distance to $10 is b
    Distance to $2/$5/$50/$100 is root(a squared + b squared) where a is the distance from $10 to $2/$5/$50/$100.

    But b is not root(a squared + b squared) unless a is zero. Therefore, if you focus at $10 distance, but recompose to $2, then $2 will not be sharp, because distance to $2 is now root(a squared + b squared) and neither will $10 be sharp because the focus - previously on the $100, distance of which is root(a squared + b squared) - is now b.


    happy reading!
    Last edited by ZerocoolAstra; 16th March 2010 at 03:30 PM.
    Exploring! :)

  8. #48

    Default Re: Advise on focusing

    this is the first time i read about the cons of focus-recompose way of shooting. hmm the theory sounds true. but the differences normally are not visible through bare eyes right?
    I love Tamron.

  9. #49

    Default Re: Advise on focusing

    Wah.. geometry and triangle also come out already

  10. #50
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Advise on focusing

    Quote Originally Posted by hoho85
    this is the first time i read about the cons of focus-recompose way of shooting. hmm the theory sounds true. but the differences normally are not visible through bare eyes right?
    referring to the triangle I posted up earlier:

    If the difference in length between b and c is negligible (ie b is much larger than a), then it is likely that the subject will still remain in focus... It all depends on the depth of field, of course.


    Quote Originally Posted by ZerocoolAstra
    referring back to THIS link which catchlights had posted earlier:
    If b is very large (eg. one end of a football field to the other) and a is comparatively small (eg. 20cm), you won't notice the problem of focus-recompose...
    Last edited by ZerocoolAstra; 16th March 2010 at 06:18 PM.
    Exploring! :)

  11. #51

    Default Re: Advise on focusing

    Quote Originally Posted by ZerocoolAstra View Post
    following on from wildcat's post...:



    Aim at $10. Distance to $10 is b
    Distance to $2/$5/$50/$100 is root(a squared + b squared) where a is the distance from $10 to $2/$5/$50/$100.

    But b is not root(a squared + b squared) unless a is zero. Therefore, if you focus at $10 distance, but recompose to $2, then $2 will not be sharp, because distance to $2 is now root(a squared + b squared) and neither will $10 be sharp because the focus - previously on the $100, distance of which is root(a squared + b squared) - is now b.


    happy reading!
    WTH!!!

  12. #52
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    Default Re: Advise on focusing

    Quote Originally Posted by hoho85 View Post
    this is the first time i read about the cons of focus-recompose way of shooting. hmm the theory sounds true. but the differences normally are not visible through bare eyes right?
    If you are lao hua (long-sighted) and don't wear the correct glasses, yes, it's not noticeable.

    On a more serious note, this is VERY obvious when you shoot macro.

    It should be obvious whenever you use big apertures "close up" anyways.

    TECHNICALLY, it is more complex as you have to factor in the focal length bla bla bla.

    Use a DOF calculator and play around with it to get what I mean: http://www.dofmaster.com/dofjs.html

  13. #53
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    Default Re: Advise on focusing

    I don't know if anyone has mentioned this already, but I just happened to remember something I tried before to resolve the same problem TS has.

    That is, to use the 3D tracking mode. Set the AF to AF-C and choose the crosshair thinggy. Now when you lock your focus, the crosshair will follow the spot as you move your camera.

    It works (somewhat), but the down side is that it's slowww and it's also not that accurate so you have to move your camera slowwwwly and double check that the crosshair is actually pointing to the correct thing that you want in focus.

    How to set 3D tracking mode? Please consult your manual or ask Mr. Ken Rockwell.

  14. #54
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    Default Re: Advise on focusing

    Dear All,

    I appreciate what everyone has suggested to me. I understand what is everyone saying and I have tried it out. Thank you.
    Nikon D90 | 18-55mm f/3.5-5.6 | 55-200mm f/4-5.6 | 35mm f/1.8G | 50mm f/1.8D

  15. #55

    Default Re: Advise on focusing

    This thread fierce like dragon...

    Just use AF-A and single point.

  16. #56
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    Default Re: Advise on focusing

    You guys just make mountains out of molehills.
    Home is where the heart is.

  17. #57
    Senior Member ovaltinemilo's Avatar
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    Default Re: Advise on focusing

    Hi everyone and eltonteo...Chill...chill...dun get so worked up...tt might be alot of reasons to ur oof issue...ultimately everyone who commented was trying to help you...

    hmm...why not u post ur pic + tell us what u see on your setting so tt we can help further?

    ways to try:
    -first of all u got to make sure ur lens is really working fine...try to confirm it's not a lens issue first..test w/o recompose to make sure the focus is sharp
    -then do it again with recompose and see wat's the diff..if focus point changes, where is it nw?
    -also, take note of which af selector is activated and did u make sure the green dot stays when u pressed the shutter?
    -try to snap a static object as compared rather than a hyperactive kid who tends to move about...

    Photography actually has alot to do with patience in sm ways...dun get frustrated too early...try n try shd definitely get better....
    ...:::..::.Nikon.::.:::..
    RGB Metering & Focusing.

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