Small complaint about D300 Autofocus

Discussion in 'Nikon' started by tom_luongo|1, May 7, 2008.

  1. Why aren't the D300 AF cross sensors spread throughout the viewfinder instead of
    the 3 center columns? Every once in a while I find I'm in a situation where the
    horizontal sensors don't quite cut it.
  2. Can you imaging the size of the piggy back mirror, at the back of the main mirror, that reflects the light to the AF unit in the bottom of your camera, when you spread the AF through whole frrame?
  3. Tom is talking specifically about the 15 central cross-type sensors:

    The AF area is already quite a bit wider than this, but the outer sensors only operate in a single axis and so can be less effective depending on the orientation of the subject.

    I don't know the answer to this question - placing them along a horizontal line might seem a bit more logical, but the D300 has some quite complex AF modes that use sensors in various combinations, and perhaps there were technical limitations on where the x-sensors could be placed.
  4. Though you never hear anyone complaining about it, on a D3 the clustering of the cross-sensors is even tighter. Does anyone know where I can find a diagram of the "piggy back" mirror assembly? Sounds like something behind the primary mirror which must be only partially reflective so that light passes through and reaches the AF unit. If they reduced the reflectivity, would that improve AF performance at the expense of having a dimmer viewfinder? If I could spread out 8 more cross-sensors, I'd probably add them something like the image below. Maybe they are working on this for the D400.
  5. Personally I want sensors further out than they are now. It leaves too much area I have to maneuver the camera around to get a good sensor to use.

    I want the edges smaller.....

  6. The more you move off the optical axis the more difficult it gets to find exact focus. So it is not that Nikon is just not aware of the problem it is just technically more difficult and more inaccurate to have the AF points further away from the center.

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