seany wrote in post #18251828
New to the Nikon family, was previously a 5d mark 3 user
just got my d500 with the sigma 50-100 f1.8 yesterday and did some test shots
need some advice on the af tracking
stationary subjects had dead on focus with absolutely stunning sharpness
but with a subject walking towards me i was getting very bad in-focus rates
Let's start with terminology and basic AF operation.
AF tracking is for maintaining focus on a subject while something temporarily gets in the way. It's used when you have people, grasses, tree branches, wildlife etc. that get in the way and might temporarily cause you to lose focus. With a low setting it maintains focus briefly and allows you to quickly pick a new subject. With a High setting it maintains focus for much longer but that can also delay picking up an alternate subject - or putting focus in the right place if initial focus is incorrrect.
The situation you describe is 3D Focus tracking. The camera stays focused on the same subject, but adjusts as the distance to the subject gets closer - or further. This is especially good if you have bright color in the image. I don't normally use this mode, but it is intended for the situation you describe.
For any moving subject - and general use, AF-C supports focus for moving subjects and the defaults allow the camera to fire when it is slightly out of focus. The default is the camera fires when you press the shutter release. AF-S requires focus be achieved to fire - and it refuses if the subject is out of focus or it thinks it is out of focus. AF-Auto automatically decides between AF-C and AF-S, but my experience is it struggels when a static subject starts to move so I NEVER use it.
You don't mention how many focus points you are using. Generally you should use the smallest number possible. I use Single or Dynamic 25 points. The approach is to put the AF point on something with sharp contrast - a tree branch rather than a bunch of leaves or a person's collar rather than just the person. Ideally you want to focus on the eye of a person or animal, but if they have sunglasses or glasses, you might focus on something else in the same focus plane - the neck, the shoulder, etc.
Group AF uses a group of 5 AF sensors as a single sensor. It's less precise but a good alternative to Dynamic 25 point. Group tends to bias focus in favor of the closest subject in the group - but that may mean it picks up a foreground branch or blade of grass. Dynamic 25 point uses one AF point but uses the rest of the group to help. It is great for birds in flight or rapidly moving subjects, but it may miss focus and pick up something in the background. I use Single point, but will also use 25 points and Group if needed. Don't just let the camera automatically select unless you really don't care - like a photo of a flock of birds up close.
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