Correct focus?

Discussion in 'General Technical Discussion' started by cwilt, Aug 16, 2005.

  1. cwilt

    cwilt

    Apr 24, 2005
    Denver, CO
    What is correct focus regarding DOF? If the intended target is in focus where should the rest of the in focus area be? Does Nikon, or any other company for that matter, have a spec for this?


    Just wondering. :wink:
     
  2. Chris101

    Chris101

    Feb 2, 2005
    Arizona
    It's not a Nikon thing, but an optics thing. Because of the way perspective makes further things smaller, the DOF extends approximately one third toward you from the focal plane, and two thirds away from you. And of course the smaller the aperture, the wider the one third in, to two thirds out distance will be.
     
  3. jfrancis

    jfrancis

    May 8, 2005
    Orlando, FL
  4. cwilt

    cwilt

    Apr 24, 2005
    Denver, CO
    Do you think this is acceptable then?

    [​IMG]

    Focus was...

    [​IMG]

    70-200vr, 1/60@f4.5, 200mm from about 8 feet. That gives 0.03 feet DOF. No sharpening was applied. Am I measurebating this to death?

    I don't know if I should send my D2x in for focus issues or not. I need help!
     
  5. This is what I get at 200mm, f5.6, hand held with flash. 100% crop.

    [​IMG]

    The trouble with the wee ones is they are perpetual motion subjects. I would try a static subject such as a sleeping child to be sure. You can always send it in for them to test and adjust the focus.
     
  6. JeffKohn

    JeffKohn

    Apr 21, 2005
    Houston, TX
    Charles that looks a bit front-focused to me, look how sharp the crud in his nose is. :)

    But I agree with Beezle it may be hard to judge from this one shot whether you have a camera problem, since there could have been some last-second subject movement. Also depending on how exactly the focus sensor lines up with the visible bracket it may not have actually caught enough of the eye to grab solid focus.

    On the other hand I think you've had enough shots like this to be concerned, I think some more rigorous testing may be called for.
     
  7. cwilt

    cwilt

    Apr 24, 2005
    Denver, CO
    That is what I am seeing as well.

    My next plan is to test the focus sensor to bracket alignment.

    I agree. It seems odd that I am just now finding a front focus issue. If the focus sensor to bracket alignment looks good then I will send it in. Now I have to remember where I put my D70 stuff. :roll:
     
  8. I believe that the red focus bracket is superimposed over the area of the image where it was the moment the exposure was made, not the actual point where you focused unless nothing moved.

    I may be wrong, but I know I was perplexed by this when I checked some focus points on my pictures.

    Woody
     
  9. JeffKohn

    JeffKohn

    Apr 21, 2005
    Houston, TX
    But if the subject's head moved back a tiny bit before exposure, the AF system may not have had a chance to adjust focus (especially if Focus Lock-on was enabled). Also looking at the indicator, it's mostly on the area under the eye and not the eye itself. If the actual sensor isn't exactly aligned with the indicator it could be trying to focus on the skin underneat the eye which is pretty low-contrast.
     
  10. cwilt

    cwilt

    Apr 24, 2005
    Denver, CO
    This is not the first time I have seen front focus in one of my images. Even shooting static subjects from a tirpod has produced front focus. My D2x is in a box waiting for over night shipment to Nikon as I type this.

    If I had posted the full image you would see that the shirt which is closer to camera is what is in sharp focus.

    Logan doesn't stop moving often so I have learned to wait for the pause then focus and fire.

    Got my D70 off the shelf today. My lenses are now bigger than my camera. :lol:
     
  11. I'm not the expert of course but this seems similar to my experience with the long lenses (see that thread in this forum)

    One of the overall conlusions was that I was measurbating this to death, I tried to get the poor camera to focus dead on on a flat surface, at a very close distance with a large apertyre. DOF was so shallow that it was just an unfair test. Paul convinced me to go to F8 and higher ISO (500mm lens) and that helped the problem go away. I suggest you consider closing the lens down a bit, you might just be needing a bit more DOF.....
     
  12. cwilt

    cwilt

    Apr 24, 2005
    Denver, CO
    Andreas,

    The camera in question is at Nikon with a repair rank of B2. Minor repair with major parts replacement.
     
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