Why will Nikon D3100 not focus automatically with AF-S Lenses

I just purchased Nikon D3100 that came with the Kit Lens 18-55.
I have camera set to AF-S mode by toggling the switch from A(Automatic) to M(Manual) on lens. I did this
so I can set the 'focus point' I wanted.

However, after setting the lens to manual, camera will not 'drive' lens to autofocus. Am I doing something wrong?
How do I get camera to Autofocus after it is set to AF-S.

Any help will be greatly appreciated.


  • edited February 2018
    There is a fundamental problem here with terminology. When the lens is set to manual, autofocus is disengaged. That's what "M" means in this context. "A" is auto focus, and variations in the working of auto focus are done only within the camera.

    I think what you are trying to do is to get out of "Automatic area" mode (a wise decision) but you need to do this in the camera.

    To change auto focus modes one must go to the camera's menu. The [i] button is the quickest route to this. Hit that button, use the cursor to go to one of the two auto focus settings, and reset there. Here is what you get:

    The camera itself can choose two different modes of auto focus. One is AFS, or single servo autofocus. When thus set, the camera will focus once per shot. If you hold the shutter button partway down after it hits focus, the subject or the camera can move, and the focus will not change. Best for static subjects. You can choose to have a focus confirmation beep. If you want to focus and recompose, AFS is needed.

    The other is AFC, or continuous focus. When thus set, the focus will continue to adjust as the camera or subject moves.

    You'll find two other choices here: AFA is a combination of the two above, in which the camera starts in AFS but if it detects movement, it will (or usually will) switch to AFC. It works pretty well but is not foolproof. M is manual, in which all auto focusing is turned off. When you want manual focus, you can use either this or the switch on the lens. They are redundant.

    Separate from these settings is a focus area setting, in which, depending on the mode chosen, you can set what is focused on and how movement is followed.

    Auto Area, available for either AFS or AFC, allows the camera to choose a focus point. The camera will tend to find the closest thing it thinks is a subject, and focus on that. In the viewfinder you'll see little lit dots telling you where it's chosen, but you have no control here. It may be good for group snapshots of people, and for hip shots where you don't have time to compose, and I've seen it occasionally recommended for isolated subjects like a bird in the sky, where there's only one possible subject anyway, but for the most part I think it's a setting to avoid.

    Single area, available for both AFS and AFC, focuses on a spot you choose, using the rear control. In AFS the focus will not change. In AFC, if the subject stays within the area, focus will follow it. If the subject leaves the area, it will not follow.

    Available only for AFC (or AFA when when it chooses) are also dynamic area and 3D modes. In each of these cases, the focus will begin at the point you select. In dynamic area mode, focus will follow a subject if it moves out of the starting are to one of the others. In 3D much the same will happen, but the camera uses color and other processor information to try to figure out where it's gone. It's more likely to jump around, can miss or switch subjects at times, but if a subject is unique in the frame, it can track even irregular motion. Dynamic area mode tends to be more consistent for nature shots where color information is spotty, which 3D is sometimes recommended for sports where a subject of distinctive color can be tracked. In 3D mode you will see little red lights to show where the tracking is occurring. There are no lights in Dynamic Area mode except the starting point.

    In all cases except Auto Area, you choose the starting point using the rear arrows on the camera. To recenter quickly, push the [OK] button. The point you choose will be shown in the viewfinder.

    This is only for viewfinder mode. In Live View the options differ somewhat, but there is still an AFS for single servo, and an AFF for following motion, with some different options. Live view focusing is slower and less able to track motion, but accurate.

    Remember, though, that AFS will only focus once per shot. If you want it to re-focus you must release the shutter and refocus. If you want to recompose after choosing focus, you can do that by holding the button halfway down, and moving the camera before you shoot.

    In both focus modes, the camera operates only in "focus priority," which means that if it cannot lock focus, it will not shoot a picture.

    If you're shooting in dark or poor light, you'll probably have to switch to manual focus or find a bright spot near your chosen distance, focus on that, and recompose.

    edit to add: the most sensitive and fast acting focus point is the cross-type point in the center. If you are having difficulty focusing, or working fast, chances are you'll do best using that one. If you're shooting static subjects in good light, moving the focus point may be a little more accurate than recomposing.

  • edited February 2018
    By the way, do not feel bad about some of this terminological confusion. Nikon has a tendency to repeat terms and designations in a way that makes it almost inevitable. AFS designates a lens with an internal motor, and AF-S designates single servo autofocus. It's a big little hyphen there!

    Actually, cancel that! Nikon itself uses the hyphen for AF-S lenses as well. So it's exactly the same terminology for two entirely different things.
  • Wow Thanks Bruto! for very well and detailed explanation for understanding the key differences between AF-S and AF-C modes. It is very clear to me now that with AF-S, my DSLR auto-focuses once and afterthat if I continue pressing the shutter down half away, then even if the subject is moved the focus will not change and remain the same. With AF-C, it is slightly different as autofocus changes everytime you move the camera or change the subject.

    However, my concern was regarding the change to little lit dots that you see in viewfinder. This was because I wanted to take a landscape photography where I wanted to focus on swan hiding behind the trees. The camera, like you suggested, was finding the closest thing (ie trees) as a subject and not focusing on swan. This was bit irritable which made me to raise this question in the forum.

    However, reading your detailed response and reading this link posted by Moose himself https://www.cameratips.com/d3100/landscape-settings-tips-tricks ... I was able to resolve this by changing the Auto Area Mode from AF to Single Point AF. This helped me to change the viewpoint on little lit dots and focus on swan.

    Thanks for the time and effort given by yourself Broot.
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