Focus Motor Question

Discussion in 'Nikon' started by rjmelone, Nov 13, 2012.

  1. I believe the focus motor on my D90 is failing which is no longer under warranty. I understand that both my D90 and my Nikon lenses have built-in focus motors. Here are my questions: First, is this correct? And second, is there a way to turn off the focus motor on the D90 and use only the focus motor of my Nikon lenses? Thank you!
     
  2. Which lenses do you have? Only AF-S Nikkors have built-in motors.
     
  3. pge

    pge

    My understanding is that if the lens has a built in focus motor then it does not couple with the camera focus motor at all. No need to turn it off.
     
  4. Les, all of my Nikon lenses are AF-S. Thanks!
     
  5. If you don't have any non AF-S lenses, why do you suspect that the motor is failing?
     
  6. I am trying to rule out a failure with the camera's AF system. Other than that, please advise Elliot.
     
  7. "...if the lens has a built in focus motor then it does not couple with the camera focus motor at all."
    Exactly. If an AF-S lens is mounted, not only does it not mechanically couple with the in-camera motor, but the camera also knows not to activate the in-camera motor. It's already "turned off".
     
  8. You are saying that when you attach an AF-S lens to a D90, the focus motor of the lens is auto-activated. That would suggest I have a double failure of two Nikon lenses (300mm f/4 and 70-300mm VR II); something that seems very odd to me. So, is there a way to turn off the focus motor on the lens and activate the motor on the camera? My point is: we have two focus motors available correct? The lens and the camera. If one fails why not activate the other in order to determine where the problem is? Is this possible?
     
  9. "So, is there a way to turn off the focus motor on the lens and activate the motor on the camera? My point is: we have two focus motors available correct?"
    No. You do not have two focus motors "available". The focus motor in the camera has a mechanical coupling at the lens mount face for AF-D lenses. AF-D lenses have a corresponding mechanical gear train to couple to this motor. Your AF-S lenses do not have this mechanical coupling (or associated gear train). AF-S lenses are focused solely by the motor inside the lens.
    If you are having autofocus issues with multiple AF-S lenses, then the first thing to try is to clean the CPU contact strip inside the camera mirror box. Use a tightly wound cotton swab (Q-tip) moistened with pure alcohol. If that doesn't cure the problem, then you are probably going to have to bite the bullet and send your D90 to Nikon for a more thorough diagnostic inspection.
     
  10. Michael --- thank you! But, I don't understand the logic you are suggesting. If I am having auto focus problems (i.e. auto-focusing on distance objects) and the focus motor that is being used is in the lens, then why would I send the camera in for dianostic inspection. Why wouldn’t I send the lens in instead?
     
  11. The chances of having two lens go bad at the same time is very small . Hence the advice to clean the electrical contacts on the camera . If this does not solve the problem then pehaps the fault is in the electronic connections on the camera not the lens .
     
  12. Robert, sending the lens would make sense if you had one lens with a problem - but you say you have two lenses with the same problem. That makes it less likely to be the lens at fault.
    To understand what is happening: the motor is just a motor - it moves lens elements according to what the AF unit in the body thinks is proper focus distance. So, the body tells the motor where to move. For this, there is electronic linkage between the lens and the body. As you have two lenses showing issues, most probably, these electronic contacts are having problems transmitting to the lens. Dirt is the most likely cause.
    So, what Michael suggests (and what is indeed by far the most logical), is cleaning these electronic contacts on the body, and if that still does not resolve it, Nikon will have to check whether these contact points still work properly.
    Hope this helps a bit in making more sense?
     
  13. The focus motor in the lens moves the lens elements to achieve focus, but the brains to tell it what to do are in the camera. As you noted earlier, to have a simultaneous failure of two in-lens AF-S motors is unlikely, so if you are having focus problems with multiple lenses then the fault probably lies with the camera body.
    As I noted above, try cleaning the contact strip that is at 12 o'clock inside the camera mirror box. This is the path for logic communication from camera to lens (and electrical power to the AF-S motor), and if one or more of these contacts is oxidized (it may not be visible) that may cause problems with autofocus function.
    If you have access to a friend's or relative's Nikon body, you could try your lenses on another body to eliminate another variable. If the lenses work fine on another body, then obviously the problem lies elsewhere.
    If you can't isolate the problem to the body by trying your lenses on another known good body, then the best course of action would probably be to send both the lenses and the D90 to Nikon.
    But clean your CPU contacts first. First in the camera mirror box with a Q-tip, and also the lens CPU contact blocks (use a soft cloth moistened with alcohol).
     
  14. Thanks very much everyone. This has been a tremendous help!
     
  15. I want to also mention that I am using rear (AE-L AF-L) focus on the D90. I am going to switch this back to the shutter to see if this makes a difference with the auto-focus problem.
     
  16. Robert, exactly what kind of problems are you having? You mentioned something about problems focusing on distant subjects. Does the camera do an excessive amount of hunting (focusing back and forth while trying to achieve focus) or does it just fail to do anything at all? Are we talking about low-light situations or bright light?
    If the camera randomly doesn't do anything when trying to focus, switching back to the shutter button may help if the button on the back of the camera is going bad. If things return to normal, then the AF-L/AE-L button is probably going bad. Probably not an expensive fix if you want to send it in. If things stay the same, the problem is elsewhere. Most likely with the contacts. Dirty contacts is a fairly common problem. I hear that a pencil eraser is a good tool to clean contacts. If the camera, instead, does a lot of hunting back and forth, that opens up a longer list of possible causes.
    Just to clarify a bit more, AF-S lenses have no linkage to connect with the in-camera focus motor. The camera knows this and automatically disengages the in-camera motor when an AF-S lens is attached. Therefore, if you are having problems focusing an AF-S lens, the in-camera motor has nothing to do with that.
     
  17. I hear that a pencil eraser is a good tool to clean contacts​
    Not realy, normal pencil erasers are very abbrassive, and may damage the gold layer of the contacts. Apart from that they crumble, and you do not want the crumble inside of your camera at all..
    The felt tip method is a much saver way to clean the contacts (both on lenses and in camera contacts )..
    If you are having autofocus issues with multiple AF-S lenses, then the first thing to try is to clean the CPU contact strip inside the camera mirror box. Use a tightly wound cotton swab (Q-tip) moistened with pure alcohol. If that doesn't cure the problem, then you are probably going to have to bite the bullet and send your D90 to Nikon for a more thorough diagnostic inspection.​
    Another suspect may be a an older camera battery, battery's older than 3 / 4 years may provide you with insufficient current to drive the camera & Focus motor in the lens. New (well charged) batteries somtimes work wonders...
     
  18. Cory, to answer your question, the D90 focuses quickly on close objects, but when I go from a close focused object to a distant object like trees, there is no hunting, just blur. This is in bright sunlight. I would say that this happens one out of every three attempts. The other times it does lock in. I've been shooting for a while, so I don't believe this is a technique or setup issue.
    C.P.M., Excellent suggestion about the batteries. I've been switching between two sets of Nikon batteries for about three years with the D90. If all else fails, I will buy another battery to see if that helps.
    I should point out that I am an extensive bird photographer and my thumb is on the AE-L AF-L button constantly while tracking birds. I can see where this could be a strain on the AF system of the D90. To what extent, I don't know!
     

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