steve_stoneblossom Loc: Rhode Island, USA

Having read another member's questions regarding autofocus modes got me thinking about my own issues when using my D7100.

I am trying to optimize autofocus when tracking subjects walking toward me as I stand off to one side.

To test, I used 2 scenarios. First I shot people walking towards me on a city sidewalk, while trying to maintain center focus on something they were carrying, often a coffee cup. Second I shot vehicles approaching me on the street, trying to maintain center point on the license plate. Shots were all at f5.6 (the low limit of my lens and supposed high limit of autofocus). I was trying to compare results of AF-C using single point focus, center focus point, and AF-C using D-9, where camera is supposed to choose one of the 9 center points in the event that the subject leaves the center point.

I shot in JPEG basic, just so the buffer would not interrupt shooting bursts. Shot some in continuous low speed and some in continuous high.

I then set my review screen to highlight the focal point.

As expected, when shooting using D9, the focal point occasionally jumped from the center point to one of the 8 surrounding points. When shooting using single point, it was always the center point.

What disturbed me was the number of times there was no highlighted point, which happened in both modes, between 10 to 15% of the time. Most of these shots seemed to focus similarly to the previous shot, which could be OK, so long as it's only 1 shot that does not focus, as DOF should be sufficient. But when 3 or 4 consecutive shots do not acquire a focus point, now the subject has moved enough that focus is clearly off. There was one 50 shot burst where only five or six of the first shots in the burst showed a focus point, the camera never re-acquired a focus point, and (not surprisingly) the last shots were way out of focus.

Am I misusing the focus modes? Do I need to refine my testing using different lenses? Or do I need to consider having the autofocus system checked?

Pine1 Loc: Midland & Lakeway

What lens were you using? Try a higher f stop like 8 to 11. Shoot with 9, 21, 51 and 3D. Lower your ISO to 100-200.Use a faster shutter speed. Are you hand holding or using a monopod or tripod. With a tripod and monopod try turning off the VR.The D7100 is a great camera and I'm sure you will get it to do what you want. I've been using mine for 8 months. I've had 6 hours of one-on-one tutoring and I am just now starting to understand how powerful this camera is. Good luck.

Pine1 Loc: Midland & Lakeway

By the way, I keep my camera on AF-C for anything outdoors and 9 focus points. I find that I get better shots with my 105 f2.8 Macro and 70-200 f2.8.

steve_stoneblossom Loc: Rhode Island, USA

Thanks for the reply. I may need some one on one as well.

amehta Loc: Boston

I think the 3D-tracking mode would work better for this scenario. I wonder if back button focus might work better, since you could keep the AF activated the whole time, rather than releasing it each time you release the shutter.

You have the AF-C priority set to release priority, so the camera is shooting regardless of the focus. If you use focus priority, it will not take the picture when it does not get it in focus, and you will see that happening (custom setting a1).

liv2paddle Loc: Wall, NJ

http://www.everythingd7000.co.uk/autofocus-guide/

This may help you. ..perhaps a3 change to none to speed up focusing and try switching to focus priority a1 to see if focus point shows up more.I always leave af-c on release and get similiar results as you but I am shooting wildlife and want quick focus with no hesitation.

OnDSnap Loc: NE New Jersey

:thumbup: :thumbup: To and fro focusing is the most difficult because of the constant changing of distance, worsening the matter is shallow DOF...3D tracking mode should do the trick/help... where for it uses color, brightness and distance information to auto focus. Try using some bright color as your focal point where the subject (bright color) and background are quite different, the source of the color and distance information will then be used to track the subject coming toward you, also having the 39 focal points and initially selecting one will help being (3d) is using several methods of auto focusing...BTW, 3D needs a D or G series lens for it to work.

steve_stoneblossom Loc: Rhode Island, USA

Thanks, all, for the suggestions. I will re-check my settings and give them all a try as soon as I am able.

skiman Loc: Ventura, CA

Yes 3D mode was made for your situation.

tmicro Loc: Walkertown,N.C.

I find with the D-7000 that 3-D works very good as long as there is not to much contrast. I use it for my two small dogs running around in the yard. nothing but green grass and brown or white dogs. When there is lots of other back ground colors it does not fair as well.

steve_stoneblossom Loc: Rhode Island, USA

While I have not had the opportunity to run more exhaustive tests, I was able to stop by my local camera shop.

First I was told that shooting in AF-C mode was causing the problem, and that I should be using AF-S. Fortunately, I only ventured as far as the parking lot to take test shots of license plates on moving cars. It only took 3 minutes to realize I had been given bad advice.

I went back to the camera store, and the rep I originally spoke to was at lunch. The second rep said that AF-S was not the correct setting for a moving subject (which was my thought from the beginning), that I should be using AF-C. He further explained that the problem I was experiencing was caused by the AF-C setting being set to "release priority", and that I should change it to "focus priority", which would disable the shot from being taken until proper focus is established in the chosen focus point (thanks amehta!).

He further explained that using any of the focal point settings other than single (i.e. D-9,21,51, or 3D) will result in the focus point jumping around, thereby making it harder to maintain proper focus on the primary part of the image I wish to focus on.

I will be testing further, but am I ever glad I did not drive home after talking to the first rep thinking my problem was solved. I'd be pulling my hair out by now!

amehta Loc: Boston

If you can keep the center point on the subject, then using center point is best. But if the subject is moving too fast for you to track well, then 3D can help.

steve_stoneblossom Loc: Rhode Island, USA

Had a brief opportunity to test shoot AF-C single focus, focus priority today. Seems to produce the best results so far, though as you suggested maintaining focus on a specific point proved challenging. Forcing me to examine my technique!

Which brings me to a second question: When shooting moving subjects using AF-C, would disabling of VR be recommended or is it still contingent upon the usual criteria (focal length, shutter speed)?

amehta Loc: Boston

The VR does slow things down, increasing shutter lag. Turning it off could help the project, but you do risk more camera shake.

LoneRangeFinder Loc: Left field

I haven't done this with a car race, however, I did turn off VR when shooting Birds-In-Flight and was able to increase my rate of acceptable images. So I would try it both ways... and test your results.