Positioning DoF

Discussion in 'Photography Beginners' Forum' started by benlonghair, Jul 15, 2010.

  1. benlonghair

    benlonghair TPF Noob!

    Joined:
    Jun 1, 2009
    Messages:
    1,072
    Likes Received:
    0
    Location:
    Woodstock, CT
    Can others edit my Photos:
    Photos OK to edit
    Hi guys, this should be an easy question. I was playing with my 35 1.8 and a dog recently. I don't have any of the shots because I'm at work, but I can easily explain the problem.

    I have understood that your DoF should be centered on the focal plane of the lens. In other words, if your DoF is 12", DoF should extend 6" to the front and beyond of your focus point.

    Well it seems as though the DoF is actually 100% behind my focal point; that is to say the focal point is actually the back of the DoF. Everything beyond that point is OOF.

    Is this normal? Do I just have to work around it?
     
  2. Petraio Prime

    Petraio Prime TPF Noob!

    Joined:
    May 28, 2010
    Messages:
    1,217
    Likes Received:
    0
    Location:
    Ohio
    Can others edit my Photos:
    Photos NOT OK to edit

    Huh? Your post is unclear. Try again.
     
  3. shmne

    shmne No longer a newbie, moving up!

    Joined:
    Jun 3, 2009
    Messages:
    641
    Likes Received:
    83
    Location:
    Florida
    Can others edit my Photos:
    Photos OK to edit
    I understand what you're saying, sadly I have no experience having heard of something like this.

    I've personally never used a camera or a lens where the focus is all behind the focal point. Could it possibly be a mode in your camera? I've used Nikons but never fooled around with the menu settings. Change anything lately?

    Not the best person to answer this question, but I'll poke around a bit because I'm quite intrigued by this.
     
  4. Petraio Prime

    Petraio Prime TPF Noob!

    Joined:
    May 28, 2010
    Messages:
    1,217
    Likes Received:
    0
    Location:
    Ohio
    Can others edit my Photos:
    Photos NOT OK to edit
    Depth of field is always in front of and back of the plane of focus. The depth varies with aperture and distance. The greater the distance, the more the DoF is behind the point of focus. At 1:1, it's equal on both sides of the focal plane.

    On some lenses (normal and wide-angle) the DoF is very great except at extremely close distances, and almost all of the DoF is behind the plane of focus. You can get DoF to 'infinity' at relatively close distances with WA lenses. With macro lenses used close and telephoto lenses, the DoF is more evenly distributed.
     
    Last edited: Jul 15, 2010
  5. shmne

    shmne No longer a newbie, moving up!

    Joined:
    Jun 3, 2009
    Messages:
    641
    Likes Received:
    83
    Location:
    Florida
    Can others edit my Photos:
    Photos OK to edit
    In all my searching I can't find a situation where your dof can be shifted from your focal plane. Are you using a 70-300mm zoom by any chance? Or something where your lens has a switch with a 1 mode and a 2 mode.

    I'm thinking that maybe if so, that you've accidentally switched it to the 2 possibly not know what it does. In this mode, the lens ignores nearer objects and focuses father away. Possibly making it appear as if all of your DOF is behind the subject rather than proportionally split up.
     
  6. benlonghair

    benlonghair TPF Noob!

    Joined:
    Jun 1, 2009
    Messages:
    1,072
    Likes Received:
    0
    Location:
    Woodstock, CT
    Can others edit my Photos:
    Photos OK to edit
    Here's the deal. I was focusing on the dogs eyes laying on the ground. The preview looked pretty well focused, but we know that isn't the best way to tell. Now, with the eyes in focus, f/1.8 and being about 10' away, my DoF should have about 1' in front and behind the focus plane.

    Instead the dog's eyes and tip of his nose are in focus, plus about 2' of grass in front of him. Not the 1' of grass and the whole dog as I anticipated.
     
  7. benlonghair

    benlonghair TPF Noob!

    Joined:
    Jun 1, 2009
    Messages:
    1,072
    Likes Received:
    0
    Location:
    Woodstock, CT
    Can others edit my Photos:
    Photos OK to edit

    I will, but it just looks like I missed the focus, but I know I didn't because the whole point of the excercize was to move the DoF around. When I focused on the grass behind the dog, the dog came into perfect focus.
     
  8. Petraio Prime

    Petraio Prime TPF Noob!

    Joined:
    May 28, 2010
    Messages:
    1,217
    Likes Received:
    0
    Location:
    Ohio
    Can others edit my Photos:
    Photos NOT OK to edit
    Are you using a manual-focus camera?
     
  9. benlonghair

    benlonghair TPF Noob!

    Joined:
    Jun 1, 2009
    Messages:
    1,072
    Likes Received:
    0
    Location:
    Woodstock, CT
    Can others edit my Photos:
    Photos OK to edit
    I AF/MF pretty much everything because the AF on the D60 leaves a ****load to be desired. At 10' with my 35 I'd be lucky to get it to AF on a 5 gallon bucket much less eyes. So I get close with the AF and MF the rest.
     
  10. Petraio Prime

    Petraio Prime TPF Noob!

    Joined:
    May 28, 2010
    Messages:
    1,217
    Likes Received:
    0
    Location:
    Ohio
    Can others edit my Photos:
    Photos NOT OK to edit
    You cannot 'position' DoF, only the plane of focus. The DoF is determined by aperture and distance, and always extends both in front of and behind the plane of focus.
     
  11. benlonghair

    benlonghair TPF Noob!

    Joined:
    Jun 1, 2009
    Messages:
    1,072
    Likes Received:
    0
    Location:
    Woodstock, CT
    Can others edit my Photos:
    Photos OK to edit
    You're nitpicking. I know basically how big the DoF is supposed to be and I use the focus point to position it on the subject as I want. So, yes, technically I'm using the focal point, but in doing so, I position the DoF in the image where I want it.

    And if what you say is true then my lens is not showing an accurate focus.
     
  12. shmne

    shmne No longer a newbie, moving up!

    Joined:
    Jun 3, 2009
    Messages:
    641
    Likes Received:
    83
    Location:
    Florida
    Can others edit my Photos:
    Photos OK to edit
    Hyperfocal Distance and Depth of Field Calculator - DOFMaster

    Input your equipment if you haven't used this already just to double check. Honestly I think that your auto focus is messing up. If you manually focus only does this same problem persist?

    My only thought is that it is the camera, as the lens could not be doing this.
     

Share This Page