My Tokina 11-16mm *Picture*

Discussion in 'Lens Lust' started by jStat, Aug 20, 2008.

  1. jStat

    jStat

    Dec 11, 2007
    Janesville, WI
    A couple months ago, when I got my Tokina ultra-wide, I couldn't help but notice the thing backfocusing regularly on my D80.

    Frustrated with the results, I sent it back to Tokina for calibration. They returned it, saying firmly that it was functioning within factory specifications.

    Well, unless I have it set at a large depth of field(f/8, for instance), it still backfocuses at 2.8.

    These results are from sports-related motions and so forth.
    Am I expecting too much from this lens in this context? Or is my camera just the piece that's screwing up?
     
    Last edited by a moderator: Aug 22, 2008
  2. I don't understand how a lens that solely driven by a camera body can backfocus, given that the camera tells it where to focus. I can understand this for AF-S, but not for a screw driven lens.
    .
    Wide angle AF is problematic as detail is smaller than your AF reticule - Nikon places AF warnings in the manuals of all their own wide angle lenses, and says that AF may not work well.
     
  3. I didn't think the Tokina's were screw driven? Aren't made for AP-S bodies?
     
  4. cleoent

    cleoent

    Dec 21, 2007
    San Jose, Ca
    they way i would think of it is this...

    the camera tells the lens the object is 25 ft away, the lens focuses for 25 ft, but uh oh, the lens isn't calibrated right and it's 25ft focus point is really 25.5 ft.
     
  5. Leo,

    I don't think that is quite how Nikon DSLR's work. They use something called contrast detection. Basically they focus and refocus until the focus point sensors tell the camera to stop focusing by sensing the point of maximum contrast within the focus sensor. This is true for both "screwdriver" AF and internal focus motor AF-S lenses.

    Front focus and back focus probably occur because the parts of the camera that detect whether or not the lens is focused are not in the same exact location as the sensor that records the image. The camera says i'm focused but the image is not. Extreme wide angle lenses could exaggerate the difference and you might have a front or back focus issue when very close to the subject. When further away, the depth of field inherrent in wide angle lenses probably makes up for a lot of error in focus precision.

    The engineering behind all of this is simply amazing. Today we have cameras and lenses that focus very well almost instantaneously with a wide variety of lenses under varied lighting conditions.

    That they work so well with such a wide range of focal lengths and apertures is a tribute to the tremendous amount of engineering and design put into these modern marvels.

    With film cameras and top of the line SLR's like the F2 many photographers would change out the focusing screen so they could do a better job of manually focusing different types of lenses. When the "K" screen did not work I would switch it out for a fine matte center focus area for lenses that caused the focusing micro-prism and/or split image portion of the focus screen to black out making it difficult to focus the camera.

    Warm regards,
     
  6. My understanding is that all Tokina lenses are screw driven... None have micro motors...
     
  7. cleoent

    cleoent

    Dec 21, 2007
    San Jose, Ca
    eh it was just a guess! Thank you so much for the detailed info! Awesome!
     
  8. vinman

    vinman

    Nov 15, 2006
    Upstate SC
    Tokinas are indeed still camera body driven. I've found that they tend to focus a little faster than even older screw driven Nikkors, but still pretty far behind AF-S lenses. I would presume a little slower than Sigma HSM lenses, as well; but I'm a huge Tokina fan, so I'm sticking by them (all I have are Nikkors and a few Tokinas).
     
  9. John,

    I'm curious to know how well the 11-16 lens performs on your D300 under similar conditions?

    For quick moving close in action, the D80 sensors might be locking on to the wrong thing. Using manual and pre-focusing to something like 8' at f/8 will probably catch just about anything within the 11-16's depth of field.

    Warm regards,
     
  10. kgill

    kgill

    853
    Jul 25, 2007
    Europe
    The only other thing I can think is that if you are using the lens for sports photography, I guess you aren't taking pics of a static scene? I don't notice problems with mine. One time, Steinar was trying to help me trouble shoot with a lens and suggested I go to the Nikon website and dowload VIEW NX which is free and a program that allows you to see the focus area, as you chose it when the shot was taken. That helped me review my pics and sort things out.

    I don't find my Tokina backfocusing. But I can say that I had an issue with a Nikon that I took to one authorized repair shop, and they found it was a little off at 17mm (my images were all kinda out of whack), so they sent it to Nikon (Italy) to repair, and they said that there was nothing wrong with it, that the lens performed within their 'standards', nonetheless, they calibrated it. The difference was night and day, literally. I told them that I was really sorry for Nikon that out of focus pictures was within their standard-- and they stood by their "nothing was wrong with the lens to begin with'...

    All this to say, your lens could very well be off by a tiny amount, like mine was, but how to get them just to calibrate it 'for calibration sake' and see if it makes a difference? If it's under warranty, it seems that it would take no extra effort once they test it to just calibrate it.

    k
     
  11. Isn't backfocusing a body issue?
     
  12. mikechang

    mikechang

    27
    Jun 9, 2008
    San Diego
    BillM:
    The regular focusing mechanism is actually "Phase Detection", as oppose to when using the tripod mode in liveview, it's "Contrast Detection", which is not as good as Phase Detection in focusing speed. But these are just terms, I really have no idea how the Phase Detection works...

    hotrod4x5:
    I think you are right, it should mostly the camera body cuzing the front/back fousing problem. However, I'm sure in many cases, it has to do with the build quality of the lens itself too, since we hear so much about "sending it back for recalibration" , and then it focuses just fine... (mind that they only send back the lens, not the body, so the lens is not calibrated according to the body you own, and they still work well) If a slight mis-alignment was made when putting the lens together, that might have caused the front/back focus, because some glasses are not where it is suppose to be, thus the data sending from CPU on the lens isn't exactly what's going on inside the lens (EX: the current focus position)
     
  13. kgill

    kgill

    853
    Jul 25, 2007
    Europe
    in the case of my 17-35mm it was "auto-focus calibration"...
     
  14. Mike, i guess you can send it in and give it a try, all they can do is say "no problem found."
     
  15. jStat

    jStat

    Dec 11, 2007
    Janesville, WI
    kgill -

    Yes, I have ViewNX and it's a wonderful program(especially due to being free!). I primarily do not shoot static shots, as I am fascinated by the capturing of, say, a field goal drill. With the barrel distortion, it's pretty neat looking.

    I had asked them to calibrate it, but who knows?
     
  16. jStat

    jStat

    Dec 11, 2007
    Janesville, WI
    I had been thinking the same thing. I will be at it again on Saturday, but one thing sticks out:

    I was at the local camera store, and I slapped on a Tamron 11-18mm, and it focused brilliantly, with no problem.

    Unfortunately, they will not accept a trade; preferring to stay away from Tokina for some reason.


    Maybe I should just get rid of the lens....
     
  17. kgill

    kgill

    853
    Jul 25, 2007
    Europe
    So you've looked at your images in View NX and what you focused on with your little focus sensor thingie is actually what is reflected in View NX?

    I saw this here once: http://regex.info/blog/photo-tech/focus-chart/

    Maybe you can use it to test? Are the results the same on both your bodies? Have you tried using it in a static context to test?

    I haven't noticed any problems with mine, but then again... I use it outside on great gigantic things where it doesn't always make a difference, so I haven't checked.

    Try taking it to a local camera repair shop and see if they can test it?

    k
     
  18. jStat

    jStat

    Dec 11, 2007
    Janesville, WI
    Here is one of the best examples.

    The Quarterback is standing still early on a bright, sunny evening. The Quarterback is out of focus, despite being bracketed by the camera, while the players to the left are in focus.

    [​IMG]




    He is approximately six or so feet away from me. As you see, magnification of this image is at +50%
     
  19. Is it possible he moved right at the time of exposure? You should test with a static object.
     
  20. John,

    It sure looks out of focus to me. Am I reading the shutter speed correctly at 1/1000s?

    Warm regards,