Until recently, I seldom photographed moving subjects, but I am doing a lot more of that now and have some questions about how dynamic focusing works (this isn't specific to the D7100, but that's the camera I'm using now, so this seemed the right place to ask the question). I think I have a handle on the 3D tracking mode, but in the AF-9 or AF-21 point selections, I think the camera first focuses on the point I have selected and then uses the surrounding points to assist as necessary. My question involves what happens when the subject moves away from that area of the focus screen, either thru their motion or from my reframing of the shot. In these modes, does the camera continue to focus on whatever falls under the original focus area, or does it try to follow my original target? What method do you use when you are trying to follow a target moving across the frame? Thanks for your insights.
#1. "RE: D7100 dynamic AF question" In response to Reply # 0
Take my answer with a grain of salt, and wait for other replies...
I think it could lose acquisition if the target leaves the AF sensor area chosen. People choose 9 for many sports so that the camera won't latch on to something unwanted... But if a desired subject does leave the 9AF point zone, I think the camera is likely to latch on to something still in the 9AF sensor zone.
But others will answer who use these methods regularly. I rarely do.
#2. "RE: D7100 dynamic AF question" In response to Reply # 0
Fort Worth, US
What type of moving objects are you taking photos of ?
In the action photos I shoot, I have the camera locked down to the center point and use 9 AF points and I try to fill the frame up with my subject. I have shot in other AF points and had something (people) move in the back ground and pull focus to them and ruin the shot.
When I shoot a final round shot, (2 cars, one in each lane) I do set the focus point to the farthermost car and keep enough room to capture both cars leaving.
With the D7100 I am loving the 1/3 crop. Place the subject in the box let it lock focus and you are good to go .
#3. "RE: D7100 dynamic AF question" In response to Reply # 2
El Sobrante, US
Among other things, I have started shooting my 5 year old nephew playing T-ball. You wouldn't think these kids move fast enough to cause me a problem, but I have discovered that my technique for this sort of thing is sadly lacking. I don't want to have my subject in the center of the image most of the time, so I'd like to focus on my desired target and have the camera track that target until I finish the shutter press. I can do this in the 3D mode, but with a lot of little kids running around in similar jerseys, the focus point will shift unexpectedly to a different person. I'd like to figure out the best way to avoid this problem and wondered what the specifics are on the 9 and 21 point AF. I've read the manual, but it isn't much help. Thanks.
#5. "RE: D7100 dynamic AF question" In response to Reply # 3
Shooting your son playing T-Ball I would use AF-C, with a single point. When shooting sports I prefer to set up AF-C for release priority and accept the chance of getting some shots out of focus as opposed to focus priority and risk loosing a shot altogether. I would use one of the center points to focus and not worry too much about your composition and leave that to a little cropping after the fact.
When using the dynamic point settings you always run the risk of the camera grabbing something from one of the adjacent points to lock on to. Most of the shooters in the sports forum would direct you to either single point or 9 point.
If you really want to get the shot and the correct individual in focus I have much better luck with single point, use one of the cross type focus points meaning the center point or one of the 9 points in the center of the lens. Put the selected point on your subjects chest (preferably where there is some lettering or numbers to give a good AF Target), depress the shutter halfway and follow them with that point in your viewfinder fully depressing the shutter to take the shot(s).
Marc There are always two people in every picture: the photographer and the viewer.-Ansel Adams
#6. "RE: D7100 dynamic AF question" In response to Reply # 0
St Petersburg, RU
AF-C focusing mode, 9 FP witht the center focus point as your default point is going to have the fastest response and best locking potential. Follow the scene trying to keep the center AF point on the subject you desire to be in most acute focus. It helps a lot to know the sport and players, tactics etc to be able to anticipate the action that will come next. Use a stopped down aperture to ensure a greater depth of the area in-focus unless you want to isolate a player and blur the background for artistic effect. Depending on your distance from the subject and the subject's distance from the background, you can use that artistic effect to have the viewer's eye drawn only to your in-focus subject as the background, for example the stands and dugout, would become blurred into a soft indistinct mass of light and color. That has the effect of increasing the perception of sharpness and detail of the subject that is in-focus. This is done by opening the aperture all the way(lowest f number).
The center focusing points are more sensitive to edges or details in both vertical as well horizontal orientation. The outer focus points are more sensitive in a single orientation.
Another point to consider, the focus target makes a difference also. A subject with texture and defined edges are better focus targets than a featureless flat featureless surface. A target in deep shadows will not be tracked as well as one that is better lit or mixed with dark and light.
As others have mentioned, practice, is the key to good action photography, but great action photography is due to great anticipation skills which comes from experience and knowing the game and players well. Some of the all-time great photos by press photographers years ago were with cameras that were all manual focus and a frame rate of 1 frame per 10 seconds, manual exposure and flash that required changing bulbs for each shot. We have it so easy now that sometime we neglect to work on the practice and skill honing part. Stan St Petersburg Russia