What am I misunderstanding about AF and "auto" focus point? (BIF experts might know)

Lare

Last weekend I went out to take some pictures of skydivers (from the ground) using my D7000 and the Nikkor 18-200mm lens. Everything worked fine in all occasions except that the lens simply did not want to autofocus when set for AF-A with an "Auto" focus point.

It seems to me that this should be the ideal setup for a situation like this: I was trying to taking a picture of someone wearing a brightly-colored canopy (parachute) against a flat white sky. The lens would swing out to infinity, then back to minimum focus distance then give up. Needless to say, no shot. Just to see if it was the lens, I tried the same thing with a 50mm 1.8 and got the same results.

If I went to any of the other focus points, single or multiple, things worked much better. I read and re-read the "Understanding Nikon Autofocus" document and tried to find this on the forum but didn't come up with an answer. I'm hoping that someone can give me an idea what I may have either set wrong or expected wrong from my gear. Since I was never sure when the shot was going to present itself, or how far away my subject would be when it happened, I was hoping to hedge my bets by letting the camera do the heavy lifting.

PB_PM

Rule of thumb, never trust the camera to focus on what you want it to. AF-C with single point would have been a better choice.

Msmoto

I might try AF-C 9 Point, turn focus tracking lock on to "off". The subject has to be large enough to capture with the focus spot.

manhattanboy

Last weekend I went out to take some pictures of skydivers (from the ground) using my D7000 and the Nikkor 18-200mm lens. Everything worked fine in all occasions except that the lens simply did not want to autofocus when set for AF-A with an "Auto" focus point.

It seems to me that this should be the ideal setup for a situation like this: I was trying to taking a picture of someone wearing a brightly-colored canopy (parachute) against a flat white sky. The lens would swing out to infinity, then back to minimum focus distance then give up. Needless to say, no shot. Just to see if it was the lens, I tried the same thing with a 50mm 1.8 and got the same results.

If I went to any of the other focus points, single or multiple, things worked much better. I read and re-read the "Understanding Nikon Autofocus" document and tried to find this on the forum but didn't come up with an answer. I'm hoping that someone can give me an idea what I may have either set wrong or expected wrong from my gear. Since I was never sure when the shot was going to present itself, or how far away my subject would be when it happened, I was hoping to hedge my bets by letting the camera do the heavy lifting.

LOL. I used to have so much trouble with the autofocus on the D7K too that for a while I went down to just a single focus point (made sure I got what I wanted; I also wonder if some of the D600 problems are because of the old D7K autofocus module). I've moved on to the D7.1K and things are marginally better but not always perfect. Now, I just shoot everything in CH and make sure I get 5+ shots of everything I really want (it's been my experience that there is incremental focus adjustments as you start shooting greater than 3 shots in a row). I think the lens makes a little bit of difference too. The professional lenses just snap to focus and maintain it better with less hunting... I did not believe this at first, but in my (limited) experience even a simplistic autofocus mechanism with a professional lens gives better results than a 50+ point autofocus with a consumer lens. Others may chime in differently, however.

One thing that is puzzling is that you claim you couldn't take a picture. Normally you should be able to snap regardless of whether it is in focus or not. Back button AF may might be worth trying too.

Parke1953

I think PB_PM and Msmoto got it right. I have focus tracking with lock on turned off when things are coming at me fast. Try it see what happens.

Photobug

I think PB_PM and Msmoto got it right. I have focus tracking with lock on turned off when things are coming at me fast. Try it see what happens.

+1 for Msmoto and PB_PM. My experience with the D7100 supports both comments. AF-C with single point works best for me.

FreezeAction

+1 for Msmoto and PB_PM again.

What they wrote is absolutely correct. I've shot sky divers that way, Air Force, Navy, Army, etc team competition and got them all in focus. This is one area where Nikon trumps every Canon camera in production except the 1DX and then I'd rather have a D4 for another 45 minutes or so.....

Coastalconn

First of all I would turn AF-A to AF-C. I have found AF-A tries to pick a non-moving target first. I shoot a ton of BIF and I have found that 21pt AF with AF-lock set to long works best for me. I know BIF is different than your situation, but I have found with lock on set to long I can track birds that fly behind/through trees. With it off I have found it will instantly switch to what is in the foreground. If I loose my bird, I just bump my AF until it finds my target again. I have also found with af lock on switched to off, it is so sensitive with single point, that if say a large bird like an eagle flies by and you are focused on a wing, as soon as the wing goes down the camera will switch to the background. I know my views are different than many others, but it has worked very well for me. I only shoot birds (well 99.9%)...

Msmoto

Yup, every situation requires a different technique. For unpredictable movement the 21 point is better, and for sure if foreground obstacles(trees) can get in the way, the focus lock on set to mid- long is required. One problem with lock on is if you cannot "find" the subject and the camera locks on the background, e.g., motorcycle "incident" on a race track. They sure happen fast.

TaoTeJared

A few notes on AF in general:
Auto focus (any mode) locks on lines, or very strong contrast. Color plays a part but it is secondary.
The smaller in frame (further away) the subject is, the longer it takes to grab focus.
The smaller the aperture (like the 5.6+ I'm assuming your lens was at) also slows focusing down.
Also to get focus (consider skydivers) in free fall you have to track at 100mph+ which means a shutter speed 1/400+.
I'm guessing optimal settings would be 1/1000, F8, ISO 100, VR turned off.

I have rarely found AF-A to be great on any body. I'm almost always in single point in either AF-S or AF-C.

You may want to post a photo or two of examples that didn't come out with the settings.

Lare

Thanks, everyone. As I said, not having done this before I was trying to hedge my bets--those guys move much faster than I expected(!) so I thought I'd stack the deck in my favor by letting the microprocessors figure everything out. I had no experience with skydivers and the things I usually shoot tend not to move fast (landscape) or are caught at rest (wildlife). Next time I'll try the ideas put forth here and see if I have better luck.

Oh, TaoTeJared, I can't really post anything because there was nothing captured. I had the focus lock on (also to be changed). But if I hadn't, it would have been a picture of the underside of a skydiver 50-100 feet above me with my camera lens focused at less than 1foot. (sigh)

So: Is there any shooting situation where "auto" IS preferred? I normally use single point for everything and use AF-S for landscapes and AF-C for wildlife, picking my point using the selector on the back or doing a focus & recompose if that's not working.

sevencrossing

Hi Lare
You might like to practice shooting sea gulls or crows or what ever is to hand

Lare

I was thinking that too. As a matter of fact, I found that there's a nearby field where people fly RC planes and helicopters. I think it might be a good start to be there some Saturday morning and practice on them. (And if they have little RC skydivers, so much the better.)

Juergen

I was thinking that too. As a matter of fact, I found that there's a nearby field where people fly RC planes and helicopters. I think it might be a good start to be there some Saturday morning and practice on them. (And if they have little RC skydivers, so much the better.)

If you have that opportunity, go for it. It is a very good school. Those RC planes are fast and small, ideal to practice.
Jürgen

FreezeAction

I was thinking that too. As a matter of fact, I found that there's a nearby field where people fly RC planes and helicopters. I think it might be a good start to be there some Saturday morning and practice on them. (And if they have little RC skydivers, so much the better.)

For skydivers in AF-C mode with spot focus and metering you might like to shoot them starting about 15 feet above the landing target if you have access to the area you would need to be in. The place where I can shoot them a 70-200mm zoom is perfect. The most thrilling shot I ever got was one of a man who had lost a leg and he was spot on the the target. At that level you should be able to get the diver with the chute fully opened. Good luck...

FreezeAction

I was thinking that too. As a matter of fact, I found that there's a nearby field where people fly RC planes and helicopters. I think it might be a good start to be there some Saturday morning and practice on them. (And if they have little RC skydivers, so much the better.)

If you have that opportunity, go for it. It is a very good school. Those RC planes are fast and small, ideal to practice.
Jürgen

Yes they are very fast. One great place to shoot the RC planes is the Top Gun show in Lakeland, FL which is coming up soon. It is still better to get to know the pilots and make arrangements to shoot when they practice and are not in competition. You can get better access to the area you need to be in for the best shots and they often will do photo op fly bys at slower speeds. The RC jets can come breezing by at upwards of 200 mph. For access at competitions you may need a membership here to get to the edge of the field. I used to have one and am renewing.
https://www.modelaircraft.org/joinrenew.aspx