Inconsistent Auto Focus

[demiro]

I've been shooting high school basketball with a D600 + 50/1.8G all season, with pretty good results. But a couple of games ago I ended up with a huge amount of out of focus shots. I chalked it up to a bad night on my part, which is very believable. I checked AF by shooting a page of text tilted at an angle from ~ 6 feet. That seemed fine. So I thought everything was probably OK. Next game I arrived early and took a lot of test shots during warm-ups, downloaded them to my iPad to check focus, and they looked OK. Shot that game, and had a keeper rate in terms of focus that was a little lower than expected, but not like the previous game.

District championship game yesterday...my keeper rate is almost zero. Missing focus by maybe 15 - 20 feet behind subject. So I adjusted AF after the game, at home, and it seems like maxing it out to -20 "solves" the problem. So maybe I'm OK, but the inconsistency troubles me. Does it make any sense that AF performance has been variable for ten days or so, before kind of falling off completely yesterday? Any reason to think I'm actually OK now? BTW, I tried the 50 on another camera and it seems fine. My D600 is fast-approaching the 100,000 click mark, but it should have some life left in it.

Any thoughts/ideas/suggestions? Maybe I'm just witnessing the demise of my camera?

Thanks.

 

[F15Todd]

And you have verified all your camera settings and focus point location? Obvious stuff but would hate for you to be pulling your hair out just to find the focus point has been inadvertently shifted left/right/up/down and you’re thinking it is centered.

 

[Jonathan F/2]

Are you shooting continuous or single point AF? Either the AF-C isn't keeping up with the action or you're mis-focusing using AF-S. Are you shooting high enough shutter speeds and at an adequate ISO for the lighting conditions? Also the 50mm 1.8G while a decent focusing lens, isn't exactly up to sports action standards like a fast 24-70mm 2.8 or 70-200mm 2.8 lens which are made for speed.

If I were you I'd stop down the 50mm to around 2.8 (to increase DOF) and use high continuous servo burst. I'd also experiment using center point focus using either 9-point in AF-C or even just use AF-S center point. The D600 will focus best in the center, so I'd use that to nail your shots.

BTW - I wouldn't mess with AF fine tune adjustments without verifying that your lens is focusing adequately in live view. Since it uses CDAF focusing, you can use live view as a base image to fine tune your lens for proper PDAF mirror focusing.

Maybe post some images so we can see how bad the focusing looks!

 

[drr1531]

It's hard to offer any advice without knowing how you have the camera set up. AF-C vs AF-S, single point vs dynamic area, etc. How far away is your typical focus point? What aperture are you shooting? Even if shooting wide open at 1.8 at 30 ft your DOF is on the order of 12ft. So focus has to be WAY off. Sounds like something is grossly wrong.

 

[demiro]

And you have verified all your camera settings and focus point location? Obvious stuff but would hate for you to be pulling your hair out just to find the focus point has been inadvertently shifted left/right/up/down and you’re thinking it is centered.

Thanks Todd. Yeah, I verified everything when it first happened, then reset everything just to make sure I wasn't missing something.

 

[Palouse]

When all else fails, or earlier, try cleaning the lens/body contacts with DeoxIt.

 

[demiro]

@Jonathan F/2 @drr1531 Settings: AF-C, f/2.2 or 2.8, 1/800, focus mode set to Single, ISO auto.

Yesterday was unique. I was shooting from stands in a 10,000 seat arena, maybe 20 - 70 feet from focal point, depending on where the action was on court. The 50 is obviously woefully short for this task. I wasn't going to get any great shots yesterday, but concerned going forward, as I'll be again shooting in a high school gym next week.

I fooled around with other focus modes earlier in the season, but found that single center point gave best results. I certainly understand the 50/1.8G is not the top choice here, but I've had plenty of decent to good outings with it this year.

Here are two shots. I may have missed focus on the first one, but the result is how all shots look. I definitely hit focus on the second shot. No excuse on that one.

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Thanks for the quick responses and suggestions.

 

[GonzoBernelli]

Have you cleaned lens/body contacts?

 

[olshroom]

And you have verified all your camera settings and focus point location? Obvious stuff but would hate for you to be pulling your hair out just to find the focus point has been inadvertently shifted left/right/up/down and you’re thinking it is centered.

Very good point. I have had that happen to me more than once. Something IO have done moves the lock button on the camera.

 

[drr1531]

Have you checked where the indicated focus point is either on the image preview in camera or in Nikon software?

 

[nuclearjock]

Clean the AF sensor. Use a rocket blower.

 

[ac12]

Here is a run down on how I shoot HS basketball:
Camera = D7200
lens = 35/1.8 (so same FoV as a 50 on your D600)
ISO = 3200
shutter speed = 1/400 sec
aperture = f/2.8
AF = C - D9 center point

It is CRITICAL that you NAIL the subject with the ACTIVE focus point.
I don't know about your D600. But as I read the manual of my D7200, the Dynamic AF on the D7200 is like rifle, not a shotgun. It has to START, ON the subject.

On the Canon T7i, it is more like a shotgun, the camera focuses on closest subject in the zone. So you do not have to put the AF point right on the subject.​

I also use single point so that I can pick out MY subject from the mass of players on the court. But this places the burden on me to place the AF point ON my subject. In this case, close does not count, cuz then I would be focusing on another player or the background.

Quote

Missing focus by maybe 15 - 20 feet behind subject.​

This sound very much like when I switch subjects. If I swing too fast from player A to B, and I overshoot player B, so the AF point is NOT on player B when I fire, I end up focusing on the far wall or bleachers behind player B.

When I do a FAST subject change, from player A to B, many times the 1st shot is OOF, the lens is still changing focus from A to B, when the shutter fires. The 2nd frame and on are usually in focus.

 

[Jonathan F/2]

@Jonathan F/2 @drr1531 Settings: AF-C, f/2.2 or 2.8, 1/800, focus mode set to Single, ISO auto.

Yesterday was unique. I was shooting from stands in a 10,000 seat arena, maybe 20 - 70 feet from focal point, depending on where the action was on court. The 50 is obviously woefully short for this task. I wasn't going to get any great shots yesterday, but concerned going forward, as I'll be again shooting in a high school gym next week.

I fooled around with other focus modes earlier in the season, but found that single center point gave best results. I certainly understand the 50/1.8G is not the top choice here, but I've had plenty of decent to good outings with it this year.

Here are two shots. I may have missed focus on the first one, but the result is how all shots look. I definitely hit focus on the second shot. No excuse on that one.

View attachment 1656022 View attachment 1656023

Thanks for the quick responses and suggestions.

If I were you I'd just shoot AF-S, aim for the floor/in-the-paint and recompose your shot. No need to use AF-C from the stands. Since you're shooting mostly X/Y axis movement, most your shots should be focus. Also check your custom menu setting > A3 > Focus tracking with lock-on. Set your AF to 1 (short) for quicker AF response if you plan on shooting AF-C. From the looks of the first shot, the camera looks like it's trying to grab focus on the most contrasty subject (background). The rest of your settings sound reasonable, so it really boils down to technique especially if you've eliminated the chance of focus error and/or bad lens.

 

[ac12]

Few thoughts

In pic#1 - if the AF point was not EXACTLY on the player with the ball, the camera could be focusing on #22 to her left, or the ladies on the bench, on her right.

The AF point in the viewfinder may not be EXACTLY lined up with the AF sensor in the body of the camera.
The sensor could be a bit right/left or up/down from the indicated position in the viewfinder.
I've heard of this, but I've not tested it with my camera, which may or may not have that problem.

If the subject is smaller than the AF sensor, as @Jonathan F/2 said, the sensor could be focusing on something else.
Example if the AF sensor covered the entire face, it cannot focus on the right eye.

Jersey. If you are close to the player, and put the AF point on a solid color jersey, the AF has nothing to focus on, and the lens may go into hunt mode. I've had that happen to me.

 

[demiro]

I'm certainly not claiming to be a great sports photographer, but I think I need to reiterate that this camera and this lens worked fine for quite a while, but then started getting wonky ten days ago, and yesterday virtually every shot missed way long. Based on that I don't think this is a technique or settings issue.

I will try to clean the contacts. Not sure about the AF sensor. Maybe that is simple and safe, but I have no idea.

 

[ac12]

Checking the AF sensor is worth a try.

You said the 50 seemed to work fine on another camera.
On the surface, that would seem to indicate the camera as the problem.

Do you have another lens to try on the D600, to see if you can duplicate the problem?

Then I would send it in, to the shop.
You may have to send in both the camera and lens, since we don't know what component is not working properly; AF motor in the lens, or AF in the camera.
It may be some interaction of the 50 on the D600.

 

[demiro]

So if I shoot in Live View AF is better than when shooting through OVF. So that points to the AF sensor, correct? So how do I clean it? Lock up the mirror and blow it out?

 

[demiro]

I shot with D600, D7100, 50/1.8G and 85/1.8G. D600 is the issue. Both lenses look good at AF fine tune of -20 on the D600, and look good with AF fine tune OFF on the D7100. Bottom line is more evidence that the AF sensor is the culprit.

Still looking for suggestions on how to clean the AF sensor. Google has not helped.

Thanks.

 

[nuclearjock]

So that points to the AF sensor, correct? So how do I clean it? Lock up the mirror and blow it out?

See item #2.

 

[demiro]

Thanks for that video jock. Unfortunately blowing out the AF sensor didn't help; nor did cleaning the contacts. I don't think this camera is worth the cost of repair, so I guess I can use it to take manually focused portraiture, not that I have a lot of call for that. I'm not nearly competent enough to shoot action with MF, but I could still use it for shots under the basket.

Thanks to all for the replies.