What are the settings and posture I should use when using the D7100 & 18-140mm for action sport? Action sport for me means my dog running towards me or away from me or running and stopping at intervals on a foot ball field.
This is what I've dedicated the last 3 months of my photography to, and I still fail.
I upgraded from a D5000 with a kit 55-200 to my current D7100 with a 70-200 F4 which should be much faster.
The fact of the matter is -- it's still really hard to get perfect focus with dogs running right at you. Better success if the dog is running perpendicular to you and you pan.
I use Aperture priority mode, AF-C, spot focusing with matrix metering, shutter speeds > 1/500 (more like 1/1000) and various apertures -- typically a stop or two down from minimum.
You have to watch your shutter speed and not let it drop below... 1/500th? 1/1000th?
Personally, I'd start with just ensuring you're at 1/1000th to help with success.
Also, if your aperture is too small (and the AF-C prediction misses ), you will have a lot of images where the dogs shoulder is in focus but not their head. I have found that upping my aperture to the 6.3 or 7 or 8 range helps with this regard by having a slightly deeper DOF. Of course, that typically means upping the ISO.