50mm f/1.4 AF-D doesn't focus well with camera in portrait orientation

Discussion in 'Nikon' started by justinweiss, Aug 25, 2009.

  1. I am using the 50mm f/1.4 AF-D on my D700. When I hold the camera in "portrait" orientation (i.e, vertically), about 25% of the time the lens has trouble autofocusing and goes back and forth without settling into focus.
    When I hold the camera horizontally, there is no problem.
    Has anyone else noticed this problem? Is my lens broken?
    Thanks.
     
  2. Which AF point are you using? You may be using an AF sensor that isn't cross-type, i.e. it can only detect either horizontal or vertical lines, but not both.
     
  3. I'm shooting in the mode that lets you select the active AF sensor from the grid of all sensors. The sensor I choose varies from picture to picture. Are you saying that some of these sensors will only work with the camera in landscape orientation?
     
  4. The center 15 points in D700 are cross type sensors which are sensitive to both horizontal and vertical contrast, the outer points are horizontal type only so they may not be good for portrait, especially in low light. This is noramal.
     
  5. Thanks. Very interesting.
     
  6. Are you just a tad bit too close? I have the feeling that sometimes, if you're at the limit, the camera will not focus too well. If you move 10 cm away, though, all is well.
     
  7. ShunCheung

    ShunCheung Administrator

    The attached image shows which 15 AF points on the Multi-CAM 3500 are cross type. To me, the fact that in the portrait orientation there are no cross-type AF point in the top 1/3 of the frame is a major weakness for this AF module on FX.
    00UJje-167817684.jpg
     
  8. shun, can you then just lock focus with the cross-type AF points and then recompose?
     
  9. Justin.... As Shun points out somewhat with his last 5 words, the D700 suffers by having the 51 AF points concentrated in the center. This comes from the fact that it is the same AF module being used in the DX cameras and the FX cameras, so it covers less of the FX frame percentage-wise. And this leaves a void around the perimeter on FX, including the most common location of the eyes in portrait orientation.
     
  10. ShunCheung

    ShunCheung Administrator

    shun, can you then just lock focus with the cross-type AF points and then recompose?​
    I have not used that approach since the Nikon F5, which was the first Nikon SLR with multiple AF points (introduced in 1996, I bought mine in 1997). There is too much time loss between focus and recompose, and also the subject distance can shift a bit when you recompost. Today, I select the AF point where I want the subject (or the subject's eye) to be, and I move the camera to follow the subject's movement for the right moment, right expression, etc. while the composition (where the subject is placed inside the frame) is constantly at where I want.
     
  11. I use my copy a great deal for portraits on my d300 in both the vertical and horizontal orientations. I have not had a similar problem.
    -O
     
  12. This, as already been pointed out earlier, is the weakness of incorporating the Multi-CAM 3500 AF on an FX body such as the D3X, D3 and D700.
     
  13. ShunCheung

    ShunCheung Administrator

    This, as already been pointed out earlier, is the weakness of incorporating the Multi-CAM 3500 AF on an FX body such as the D3X, D3 and D700.​
    Eddie, in fact I pointed that out when I reviewed the D3 back in March 2008. I had bought and used a D300 a few months earlier such that I was familiar with using the Multi-CAM 3500 on DX first. Once I got the D3, its problem on FX was very apparent:
    http://www.photo.net/equipment/nikon/D3/D3-review#autofocus
    This was what I wrote a year and half ago:
    While the 51 AF points from the Multi-CAM 3500 cover a good portion on the D300's DX frame, on the D3's FX frame, which has over twice the area, the 51 AF points only cover the center 25% of the frame. Therefore, some old-fashioned AF, lock focus, and recompose may once again be necessary. In particular, if the camera is held in the portrait (vertical) orientation, there is no cross-type AF point in the top 1/3 of the frame, where the subject typically is. It can be a problem under dim light.​
     

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