D90 Backfocus/tracking issues with Sigma 70-200mm

sammyd56

sammyd56

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Name
Sam
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I took my D90 and Sigma 70-200 with me to Wimbledon today and had to throw a lot of shots away because the camera kept focussing on the background instead of the player. I tried every option... single-point, dynamic area, auto-area and 3d-tracking but no matter what I tried the majority of the shots ended up with sharp ball-boys/crowds and out-of-focus players, even though I selected the right focus point every time and, I'm pretty sure, tracked the players accurately (they weren't even moving much in many of the shots). The camera was set to AF-C the whole time. Here are some examples:

(shutter speed by the way is over 1/1000 in both of these)

3657864691_fab383b032_o.jpg


3658658686_e5113ae713_o.jpg


Would be really grateful if someone could suggest what I might've been doing wrong as I just couldn't get the focus to stay locked on the player and stop shifting to the background :bang:
 
The 3D tracking should have been able to track the white against that background. :shrug: I've tried 3D tracking with football players and BMXers and it tracked very well.

Where does the camera say it focused?

If you haven't already switched the option on, you can if you go to the Playback option in the Menu, and switch the option on to show the focus point used. If the focus point used is on the player, then you could have focus problems. If it is on the background, then you may have 3D tracking problems. I got the 3D tracking to track a BMXer with a blue T-shirt against a blue sky, so you should have had no problems with the white against the green.

How do you have option #a1 set? Release, Release + Focus or Focus? If it is Release, then the camera will shoot even if it hasn't focussed. Although your backgrounds look perfectly focussed, so that may not be the problem. But worth a look. ;)

Also, is your firmware up to date? The last update improved focussing amongst other things.
 
No, ignore him.

I don't know about Nikon but with my 50D, I'd simply set it to centre-point focusing, with the focusing mode than continues to focus when holding the shutter release half-way down. I'd get ready to take a picture, hold down the shutter half-way and make sure it's focused properly and then push it a little further to take the picture.

Tennis isn't hard to track so there should be no excuse really!
 
Guys, thanks very much for the suggestions, I've checked the focus point on ViewNX and the results are as seen below. There is no option for focus-priority on the D90, but after doing some reading, the D90 in AF-C mode automatically sets itself to shutter-priority. As far as I can see there hasn't been any firmware updates for the D90 either. I'm starting to think I could have a lens problem :( Occasionally it will just stop focussing altogether and I have to release the lens and click it back in again to wake it up.

3659007668_9c09da7958_o.jpg


3659007612_9942b45400_o.jpg
 
Kryptix said:
No, ignore him.

I don't know about Nikon but with my 50D, I'd simply set it to centre-point focusing, with the focusing mode than continues to focus when holding the shutter release half-way down. I'd get ready to take a picture, hold down the shutter half-way and make sure it's focused properly and then push it a little further to take the picture.

Tennis isn't hard to track so there should be no excuse really!
Click to expand...

Yup that's exactly how I expected it to work, unfortunately in my case it doesn't :(
 
Had any previous back focusing problems with this combinations?

I'm not a Nikon user so not familiar with your settings but providing you are using centre spot and continuous focus tracking it should work. Try different lens and do some test shots.
 
I'm not a Nikon user.

On my Canon 1D MKIIs I can select to use the * button on the back to be the focus button. With the * held in focus tracks on what ever you are pointing at. Releasing the button locks the focus on that point, I can then recompose the shot and my focus point stays the same.

Works a treat for football when too players are coming together. The focus doesn't go straight through the gap between them.
 
Kryptix said:
No, ignore him.

I don't know about Nikon but with my 50D, I'd simply set it to centre-point focusing, with the focusing mode than continues to focus when holding the shutter release half-way down. I'd get ready to take a picture, hold down the shutter half-way and make sure it's focused properly and then push it a little further to take the picture.

Tennis isn't hard to track so there should be no excuse really!
Click to expand...
Slightly rude don't you think.

Redhed17 seems to know what he's talking about and has given some very useful advice then you come on and tell the OP to just ignore him even though you admit to not knowing about Nikons. I'd have thought you'd learnt your lesson about thinking before you type.
 
May I suggest you change the title to lure in D90 users so you may get some 'hands on' help.
 
How strange/annoying for you. I'm not a Nikon shooter so don't really know the ins and outs of the technical side, but I had no problems shooting tennis on my 450D with an old USM lens, set to AI Servo [ie continuous focus] and single central focus point.

Is the lens behaving itself? It sounds as though you've tried most sensible things with the body, maybe try shooting some traffic or other moving target with the lens today and see how it fares compared to one of your other lenses?
 
-Rob- said:
Slightly rude don't you think.

Redhed17 seems to know what he's talking about and has given some very useful advice then you come on and tell the OP to just ignore him even though you admit to not knowing about Nikons. I'd have thought you'd learnt your lesson about thinking before you type.
Click to expand...

That refererence is to CGeezer for his unhelpful comment.

To the OP, it should work as Krypitx and others have described.

Focus tracking like this is often a tough call except for top end pro cameras, but I'd have thought a D90 would gobble that up. My Canon 40D would do that no bother, but then I also have some good L lenses with quick AF. You need a camera to tell the lens what to do, and then a lens that can do it, so unless you're doing something wrong (not obviously) then I'd say check the lens.

Do all the usual stuff, like remove the battery and card, and clean the lens/camera contacts carefully with a rubber. Then do some test shots of maybe a car driving towards you, or someone jogging. If it won't do that with something like a 75% hit rate, summat's wrong.

I'd suspect the lens, but it might not be, so try it with another lens.
 
HoppyUK said:
That refererence is to CGeezer for his unhelpful comment.
Click to expand...

I'd agree he could have put it in a more positive manner but the advice certainly isn't unhelpful, it's a good idea if you're struggling with autofocus.

Use AF & select a point close to where the player will be/is and then switch to manual, choose an appropriate aperture for the required DOF - probably don't need too much so maybe F5.6 - F8. Depending where your sat you may need a little bit of panning to track the player. Worth a try !!

Simon
 
simonkit said:
I'd agree he could have put it in a more positive manner but the advice certainly isn't unhelpful, it's a good idea if you're struggling with autofocus.

Use AF & select a point close to where the player will be/is and then switch to manual, choose an appropriate aperture for the required DOF - probably don't need too much so maybe F5.6 - F8. Depending where your sat you may need a little bit of panning to track the player. Worth a try !!

Simon
Click to expand...

That technique with manual focus is fine with a predictable moving subject, like a car on a race track - you know exactly where that is going to be. But a tennis player? If you can predict that, you should be playing at Wimbledon.

You can see how little depth of field there is with a decent shutter speed - that's the problem. And if you zoom closer, it's going to get a lot less.

Ask any of the pros at a tennis or football match how they work, and it will always be servo-tracking AF. Manual is impossible.
 
on D90 you got 11 AF points, you don;t have to use centre point all the time. and i alway try to aim for big targets like the head cos it's got features like noise eyes, mouth where the camera can pickup contrast differences and thus focus on them. generally its more difficult on the body in the above 2 cases as they are wearing white, not a lot of contrast differences to pickup.

but going back to previous posts. you really should use tracking AF that will give you much better result, especially when u got it fixed when they are still (ie serving or waiting for the serve) and then click when they are in the right action, that should give prettty good result. and if you are still concerned use small aperture and get everything in focus and use software to blue out the back ground and isolate the players...it's cheating doesn't do your photohraphy skill any good but gets you the results.
 
I guess if you are in AF-C it will let you take the shot even if your lens is still hunting ? How about choose an AF point & plenty of half pressing as you track the player so that when your ready to take the shot the lens has less work to do allowing for a quick focus-shot. AF-A or AF-S wont let you take the shot until focus has been achieved so at least you will know at the time what is going on.
 
ricky1980 said:
on D90 you got 11 AF points, you don;t have to use centre point all the time.
Click to expand...


That is perfectly true unless the focus struggles to lock onto a point and then it may "jump" if it finds a better spot within the 11 points.

The answer to this porblem (which I think everyone has covered) is
1. Continuous focus has not been selected, therefore when the subject moves your point of focus is still locked on the same spot.
2. There is a focus problem with the camera/lens or combo

3. Camera/lens combo is back focusing.

Simple checks can be made to determine/delete any/all of the above.
 
Good points from Corbystock and Snapzz.

On the multi-focus points thing, remember that the AF will usually pick up on the closest point that detects sharp focus. It works really well when subjects move around or you don't want the framing smack in the centre, but the minute you get the tennis net in its sights then it will probably switch straight to that.
 
I misread the original postand thought it was a D300, so the D90 has less focus points and may not work the same as the D300. As I said before though, with a subject that different from the background, the 3D tracking should have worked pretty well.

Looking at where the camera showed it focussed, it looks like it focussed correctly, so it looks like there may have a problem if it is doing that consistently. :(

I'd try some practice shots to see if the same thing is happening a lot.

As for Kryptix's post, I don't think he was referring to my post, as we posted at virtually the same time, and he didn't have a chance to respond to my post.
 
did you take any pics with a different lens ? this would be the first thing I'd check.
 
snapzz said:
1. Continuous focus has not been selected, therefore when the subject moves your point of focus is still locked on the same spot.
Click to expand...

Snapzz, I don't think it will be this 3D tracking can only be enabled in AF-A or AF-C, both of which should do continuous focusing.

Sammy

Have you tried the combination in just AF-S and auto area. If you could take a picture focused on a person about 6-7 feet from a fence. If the person is in focus and not the fence, then there is probably not a problem with the lens.
 
-Rob- said:
Slightly rude don't you think.

Redhed17 seems to know what he's talking about and has given some very useful advice then you come on and tell the OP to just ignore him even though you admit to not knowing about Nikons. I'd have thought you'd learnt your lesson about thinking before you type.
Click to expand...


I interpreted that suggestion to ignore the 'switch to manual' post that was above Redhed's... which actually seems fair enough since I wouldn't have thought manual focus will give you much joy in these shots.
 
The camera will only focus where there is something discernable (contrast) for it to lock onto, so it's always going to struggle if it is pointed at an almost featureless area of white cloth. However this doesn't explain why sometimes it wouldn't take the shot if it was in AF-C my D300 happily clicks away taking oof pictures.

In the photos above the areas where the op appears to have attempted to focus are mainly white except for the tiny areas of the background creeping into both focus squares, therefore it's my guess that the camera's af has done it's job as it should and focussed on the area of contrast, in this case the background.
 
The 3D tracking tracks by colour, and that seems to be to be what it had done. There also looks like a enough contrast on the white areas to be able to focus to me.

Hopefully sammyd56 will find that the camera is OK and finds a way that to get more consistent results. If not, I hope it's still under guarantee. ;)
 
redhed17 said:
The 3D tracking tracks by colour, and that seems to be to be what it had done. There also looks like a enough contrast on the white areas to be able to focus to me.

Hopefully sammyd56 will find that the camera is OK and finds a way that to get more consistent results. If not, I hope it's still under guarantee. ;)
Click to expand...


I don't see any mention in the op of which actual mode the camera was in for these particular shots, just that

I tried every option... single-point, dynamic area, auto-area and 3d-tracking
Click to expand...

If the camera was focussed on a white area and the white area moved, surely the 3-D tracking would follow that, rather than shift to the darker background?
 
Pfff.... well I've done a lot of testing over the last few days but I still don't know what to think. I think I can fairly safely say that the camera/lens is back-focusing:

3682772878_576593fe99_o.jpg


3681941485_8342d272b1_o.jpg


I'm doubting though that it is far enough out however to cause the sharp scoreboards in the tennis shots.

I tried shooting cars and it was hopeless, seemed to focus on anything but the car. Look at how sharp the sign on the left is in these two shots from the same sequence - it's right at the edge of the frame where there aren't any focus points!!!

These are both 1/640 @ f/2.8

3682755492_b1fc8e244d_o.jpg


3682755390_07cc2a84e1_o.jpg


Whether it is the camera or the lens I don't know. The problem is that I can't get a conclusive result with my other lenses, 17-50 2.8 tamron and 55-200 3.5-5.6 nikon because they don't give a shallow enough DOF to really judge. I wish I could try the sigma on my D40 but the battery is dead and I left the charger in Spain :( It's really annoying not being able to find out whether it's the lens or the camera.

For info, the D90 is only a few months old and therefore still under warranty. The Siggy 70-200 was bought from whitey on here.

Can anyone suggest where I can go from here?
 
First thing I would try is to test the D90 with the Nikon lens. If you set up a test with the widest angle you should get f3.5. If this proves to be back focusing send back to Nikon. If it doesnt then its the camera/Sigma problem in which case contact Sigma.

Regarding the dead battery on the D40 try calling in at a camera shop and ask if they will charge your battery.
 
awp said:
EXIF data would help too maybe
Click to expand...

Is there some kind of magical focus troubleshooting data embedded in there? :thinking: All the pics are f2.8 and shutter speeds are 1/500, 1/640 or 1/1000. I'll dig it out if it'll help.

I've done a lot of focus tests and they don't show any serious backfocusing, it seems to be only with far-away objects... is that possible?
 
sammyd56 said:
Is there some kind of magical focus troubleshooting data embedded in there? :thinking: All the pics are f2.8 and shutter speeds are 1/500, 1/640 or 1/1000. I'll dig it out if it'll help.

I've done a lot of focus tests and they don't show any serious backfocusing, it seems to be only with far-away objects... is that possible?
Click to expand...

Yeah the issue can be localised towards the 200mm end. Certainly no reason for it to be continuous through the range
 
sorry, I didn't explain myself so well, I mean, at 200mm, the problem seems much more pronounced when focusing on distant objects as opposed to close ones
 
even thuogh the shutter speed is high this looks like motion blur to me, i dont doubt the background is in focus but im not convinced the players arent.

at the speed they are moving at when hitting the ball it might be possible that its motion blur, i mean their arms are probably doing well over 100mph or something and you arent tracking them.
 
I wish it was mate but it really isn't :thumbs:

EXIF from two tennis shots:

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Lens : 70-200mm f/2.8 D
Preview Image : (Binary data 26763 bytes, use -b option to extract)
Red Balance : 1.960938
Scale Factor To 35 mm Equivalent: 1.5
Shutter Speed : 1/1250
Create Date : 2009:06:24 19:32:13.00
Date/Time Original : 2009:06:24 19:32:13.00
Modify Date : 2009:06:24 19:32:13.00
Thumbnail Image : (Binary data 9453 bytes, use -b option to extract)
Circle Of Confusion : 0.020 mm
Depth Of Field : 3.95 m (35.71 - 39.66)
Field Of View : 6.8 deg (4.49 m)
Focal Length : 200.0 mm (35 mm equivalent: 300.0 mm)
Hyperfocal Distance : 713.19 m
Light Value : 12.3





... That should keep awp busy! :lol:
 
I'm a recent D90 user and haven't yet done any motion shots with the camera, however I've done a fair amount reading about the focus system and here's what I've learned so far from reading Thom Hongan's complete guide to the Nikon D90 (summary of his focus chapters).

The D90 has 3 different focus modes: AF-A, AF-S and AF-C.

AF-S (Single servo AF)
In this mode the camera is on 'focus priority' so it won't take the shot until focus has been achieved. So you part hold the shutter button but it won't allow you to fully take the picture until the picture is in focus. If it can't focus at all it won't let you take the picture.

AF-C (Continuous Servo AF)
In this mode the camera is on what Nikon call 'release priority' which basically means the picture is taken once the shutter button has been fully pressed, even if the picture is out of focus. If you press the shutter button half way it will begin to focus and will continue as long as the button is half pressed, if the subject moves the focus should still follow the subject.

AF-A (Auto Select AF)
In this mode the camera decides weather to use SF-A or SF-C, I think it starts in SF-A but if the subject starts to move it'll switch to SF-C. One thing to note in AF-A mode the camera will always use 'focus priority' even when it switches to SF-C.

Autofocus area modes

Single Point AF
The camera only uses whichever focus point you have selected for the focusing. You can use the D-Pad to select which one to use.

Dynamic Area AF
The camera starts focusing on which ever focus point you have selected (use the D-Pad to choose) but it will switch it if it detects the subject has moved, providing you're in AF-A or AF-C modes - this is the default focus area method for the sports scene.

Auto area AF
The camera decides which focus points to use, you have no control over this at all. If you're using a G-type or D-type lens the camera will use the colour information from the metering system and distance information to help figure out if a human subject is in front of a background.

3D-tracking 11 point
This is like the Dynamic Area AF, so you select the starting focus point using the D-Pad. The camera will then try to track the subject (in AF-A and AF-C modes), it will use the information from the metering like the Auto Area AF does too (I think). Also with the 3D-tracking the subject needs to stay within the frame. If the subject goes out of frame then it won't be tracked correctly.

He also mentions how in most auto focus systems there can be problems focusing with relation to focus tolerance and variations in the lenses. The D90 doesn't allow you to fine tune the variations like the more professional Nikons, so it's possible but rare that you'll get a lens that consistently focuses ahead or behind the focus point you select - so try different lenses, or the lens on a different body.

Another point he mentions is that the focus points are actually a different shape to which they appear in the view finder. They tend to look more like this:

359ahso.jpg


Which tends to favour vertical detail when the camera is held horizontally. If you've got a Nikon lens, for example the kit lens try that and see if you gain better results. When I have the time I'll go out and try some motion shots, although I've had a quick play just panning and had no problems with the kit lens.

Hope the info helps,

Rich
 
Looking at the OP's images - this is somewhere that the Dynamic Area AF mode/Continuous Servo combination should have performed flawlessly - bright subjects against a dark background...It looks to me that as the subjects have moved off-centre, the camera has refocussed using the centre focus-point on the background...

With the older Nikon system , one of the presets in Dynamic Area AF was that the AF could be set to refocus on furthest subject if the original subject moved away from the selected af-point...it looks as though this is what has happened here...

I had a lot of trouble setting the Dynamic Area AF to work properly in Continuous Servo configuration and I'm guessing that the D90 uses a similar system as the D2x did...
With the new D3/D3x it has been altered significantly to the way it used to work, so obviously it was an issue that needed to be resolved.

The ideal settings for this subject would appear to be Continuous Servo AF and Dynamic Area AF - the camera should track the subject if it moves out of the originally-selected AF point...
I could NEVER get this to work properly, it must be said - the focus lock would break and refocus either on a closer or more distant subject...though never as blatant as seen here...

In your situation, I would select Single Servo AF and Dynamic Area AF modes - this way the camera will stay focussed on the subject as long as the finger stays on the shutter button - so if the subject moves, you will have to re-aquire the subject before firing.
Go into the custom menu and select focus priority - this way the shutter will only fire if the subject is in focus.

Canon did have the edge with AF until the D3/D3x, I will freely admit...now it's on a par...
 
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