Autofocus on Nikon D 7100

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Labb

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Erik
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I have got the D7100. Hope some can tell me what to do.

When I shoot a static object (building or landscape), I always use single focus and the central focuspoint. But what shall I do if I wantr to photograph a moving object (like a train or a car). I know I have to set the autofocus to continuous. But will the camera automaticly TRACK the odject if I halppress the shutter?
 
on my D7000 there is a 3D tracking AF setting that would probably cover that.
 
You've got your AF area and you've got your autofocus servo mode... Two different things, but both work together.

You want to be using AF-C (continuous) or AF-A (Auto detect). I've got my D90 in AF-S and i'm forvever forgetting to change it for moving subjects.

The 3D thing is a good point.
Normally AF-C or AF-A will constantly keep focus on whatever is centre frame, but 3D dymanically follows the subject. This intelligently tracks whatever object you focused on and keeps it in focus anywhere in frame.

AF-C or AF-A is required for 3D to be available.

Obviously there are limitations, low contrast scenes will most likely confuse the autofocus + 3D.
 
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I use AF-C and 21 point dynamic AF. I recall reading somewhere that if you can keep the subject in the middle of the frame you are better off using the 9 or 21 point AF as the camera has less points to use in it's tracking calculation and should be able to react quicker.
Until I had read this I was using the max AF points (39 on the d7000 or 51 on the d7100). I found it does improve things a bit but if the subject has erratic movement you might be better using the max AF points.

Either way lots of practice and lots of clicks and you usaully get something.;)
 
Page 73 of the manual gives a very basic idea of the auto focus modes. If Im right i think the 15 central points are a more sensitive cross type focus point and may be more accurate. I usually use the centre point and crop the picture slightly to get the composition I want. I'm a bit strange in the way I mainly use single point or sometimes 9 points for birds in flight, any more and I think it can move the focus point away from the head. Its best to try it out and find out what's best for you. Also remember auto focus systems are looking for contrast, the more contrast there is the more accurate it is, whilst subjects with little contrast can give you focusing problems and are harder to get sharp.

With birds in flight look for the patterns they follow. The direction of the wind usually dictates the direction they fly in and also where they are slower or are likely to turn towards you. Tracking a subject whilst not taking a photo is good practice. Using both eyes (keep both open, honest it does work) allows you to find a bird easier than just through the viewfinder with a 300mm lens.
 
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