"AF Fine-tune" MF lens with CPU?

Discussion in 'Nikon' started by wogears, Jan 26, 2017.

  1. Hope this isn't a duplicate--tried to post earlier.

    I have been having some focus problems with a Rokinon/Samyang 85mm f1.4 (chipped version). Carefully focused pictures are a bit soft, even at f4-5.6. Is it possible to use AF Fine-tune to calibrate the "green dot" confirmation light, considering that the lens does identify itself to the camera?
    Thanks,
    Les
     
  2. Tested that with a Zeiss 100mm lens. Possible, propably changing the camera parameters then. Tested only that the value appears as set and stays as set over switching the power off.
    Dandelion: possible, probably (most probably) changing then the lens chip parameters. There is a separate procedure for that.
    Testing with your lens is straighforward and recoverable ;-)
     
  3. When I need very carefully focused images I use magnified live view.
     
  4. ShunCheung

    ShunCheung Administrator

    As Ellis says, set the camera body on a tripod and use live view to fine tune your manual focus. That should tell you how good (or bad) your lens is.
    Also keep in mind that the Samyang 85mm/f1.4 for Nikon is less than $300, a fraction of the cost of a Nikon, Sigma, or Zeiss 85mm/f1.4 for the Nikon F mount. I wouldn't be all that surprised that a sub-$300 f1.4 lens is not that great, even stopped down.
    http://www.bhphotovideo.com/c/product/859135-REG/Samyang_SY85MAE_N_85mm_f_1_4_Aspherical_Lens.html
     
  5. Though completed AF or precise MF always results in a lighted focus dot, it seems from trying various lenses, both manual and AF in manual mode, that the reverse is not quite true. If you turn off AF and manually focus a lens, the dot will light over a wider range, even if the lens auto focuses very well. For some manual lenses it's a very wide range. It sometimes helps to go back and forth, in and out of the dot-on range, to find the center point.
    It seems equally true on the D3200 and the D7100, and especially for some lenses, perhaps worse with wider ones. A 24 mm. AI lens at three feet or so can show a solid focus light over a range of several inches. In the time it takes to zero in on it, you might as well go to live view, or just focus bracket a handful of shots.
     
  6. Later edition Dandelion chips have their own AF offset facility and don't require use of the camera AF fine-tune menu.

    Samyang don't fit a user-programmable chip, so
    you have to use the camera's fine-tune.

    However, the Samyang 85mm f/1.4 suffers from focus shift as it's stopped down. This means that you can't have one setting that gives exact "auto" focus at all apertures. My solution is to back off the focus and bring it forward until the green dot just flickers on. Seems to give much better focus than getting the green dot steadily on. YMMV.

    The above focus shift issue is common with wide aperture lenses, and some of Nikon's f/1.4 lens are among the worst offenders.

    The best solution is to use magnified LiveView for focussing at the working aperture.
     
  7. I set up a moire AF test. Turned out that, at the range of about 1.5 meters (not optimal, I know), my Samyang was pretty much spot on, as was my 105 f2.8 micro. My 50 f1.4, OTOH, required a setting of -12. As soon as I can work outside without a heavy coat and gloves (Cleveland, OH, USA), I will set up a target and check my results.
    I did discover by experiment that I could set a fine-tune value for the Samyang, and it would save properly.

    Matthew: I have the same experience, and am not sure why it happens. I also notice that using the AF button while in LV gives a very close result, it can be improved by manually adjusting the lens. (That moire target realy is incredibly sensitive. I recommend it.)
     

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