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1D AF : Why does this happen? Look at these pix.

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Oliver reid

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Here is the (uncropped) picture:



I had been tracking this player with the button half down, and this is the first of 3 frames I shot as she broke into the penalty area . It appears the camera decided to focus on the ball. In the next two shots the ball was sharp and the player was soft.
e.g. (in this shot she has just passed the ball towards the camera):



My theory is that in the first shot the Af system tried to focus on the ball and then tracked it. Then in the second shot it decided, the ball having moved out of the AF area, the grass just below the center of the frame was the best choice.

Here is the meta data. Any suggestions as to how to avoid this problem would be most welcome. E.g. is AI servo really needed for a "slow" sport like youth soccer. If not I could use one shot.

TIA. Oliver

Shooting Mode
Aperture-Priority AE
Tv(Shutter Speed)
1/1250
Av(Aperture Value)
5.6
ISO Speed
640
Lens
100.0 - 400.0mm
Focal Length
400.0mm
Image Size
2464x1648
Image Quality
RAW
White Balance
Daylight
AF Mode
AI Servo AF

11:AF point selection method

0:AF point selection button + Main (horizontal) / Quick Control (vertical) dial operation

13:Number AF points/Spot metering
0:45/Center AF point
16:Safety shift in Av or Tv
0:Disable
17:AF point activation area
1:Expand(TTL. of 7 AF points)
18:Switch to registered AF point
1:Switch using assist button only
19:Lens AF stop button function
0:AF stop
20:AI SERVO tracking sensitivity
0:Standard
Drive Mode
High-speed continuous shooting
 
Oliver

Certainly seems front focussed. Why is the question. I actually think both are front focused on the grass. Just with the huge DOF of the 100-400 the ball is still in acceptable focus on both pictures.

I would probably do some more controlled tests to see whether it is the focus that is off or whether it just tracked the grass.

I never had a problem like this but i have not shot much sport during daylight and have not shot much sports using the 100-400.

--
Michael Salzlechner
StarZen Digital Imaging
http://www.starzen.com/imaging

photos at http://www.salzlechner.com/photo
 
Oliver reid said:
I had been tracking this player with the button half down, and
this is the first of 3 frames I shot as she broke into the penalty
area . It appears the camera decided to focus on the ball. In the
Click to expand...
There's a small article by Chuck Westfall somewhere where he explains the AI Servo mode of EOS 1 cameras. Apparently AI continually back and front focusses, and when in drive mode the first frame will fire immediately as you press the shutter. The following frames however have the shutter controlled by the AF circuit -- the shutter will trigger as the camera determine AF is OK. I.e. the first frame is most likely OOF, but the following frames should be on target.

Let's see...
http://photonotes.org/other/ai-servo.html

This seem to predate the 1D by a good margin. I dunno if it still holds true... Perhaps a CF/PF setting?

--
Rune, http://runesbike.com/
 
Hi Oliver,

If you selected an AF Point manually, then it will use this point. I'm assuming that you have it on Auto, which means that the camera will choose from the 45 AF points (the CF which narrow down to 11 or 7 points only effects which ones are available for manual selection; the camera still uses all 45 in AutoSelect mode).

In Auto, it is my understanding that the AI Servo system will first focus on whatever is under the central focus point, and then attempt to follow that one as the subject moves. So I'd think that if it 'loses' that subject, it'll try to reacquire, and where this will be will depend on what's in the frame.

I don't do a lot of this type of shooting, but in the soccer shots I've done, I've had the most predictable results manually selecting the center focus point, and trying to keep it on the subject. CF17 will give it the freedom to expand this area if needed. I'll shoot a little wider than I'll want in the final image, to give me a little greater depth of field, and enhance my cropping options.



Hope this helps.

--
Don
http://www.dlcphotography.net
 
Use only the center focus point and and AI servo and I think it will eliminate most of this problem. I accidently change my settings to all focus points once and got the same results that you did.

 
I generally have much better luck with AI-Servo when I select the AF point to use.

I only use 45-pt mode when it's absolutely necessary, and preferably when there's not a lot of other things in the frame that the camera could decide to focus on.
DonCohen said:
If you selected an AF Point manually, then it will use this point.
I'm assuming that you have it on Auto, which means that the camera
will choose from the 45 AF points (the CF which narrow down to 11
or 7 points only effects which ones are available for manual
selection; the camera still uses all 45 in AutoSelect mode).

In Auto, it is my understanding that the AI Servo system will first
focus on whatever is under the central focus point, and then
attempt to follow that one as the subject moves. So I'd think that
if it 'loses' that subject, it'll try to reacquire, and where this
will be will depend on what's in the frame.

I don't do a lot of this type of shooting, but in the soccer shots
I've done, I've had the most predictable results manually selecting
the center focus point, and trying to keep it on the subject. CF17
will give it the freedom to expand this area if needed. I'll shoot
a little wider than I'll want in the final image, to give me a
little greater depth of field, and enhance my cropping options.
Click to expand...
--
The Lowest Paid Concert Photographer Around
http://www.neonlightsimaging.com/artshow/final.htm
Photography -- just another word for compromise

'Since we can't keep crime in check, why don't we legalize it and tax it out of business?' -- Will Rogers
 
You already have the answer above... use the center AF point with CF 17-2, not automatic focus point selection, for action sports like soccer.



The only time I've found auto selection useful is for birds in flight.

BTW, I tried CF 17-1 today per SI's recommendation and didnt' do as well as with 17-2 (which used to be their recommendation). Back to 17-2.

Nill
~~
http://www.toulme.net
Oliver reid said:
bump
Click to expand...
 
have to disagree with somebody.

I am always using 45pt AI Servo and dont have much of a problem. There are some pictures where the focus picked up a different target but generally it is when i acquired the wrong target. Cant remember a shot where the target was obviously lost. I shot a bit of football now and in football there are always a bunch of people around the 'target' so you would think it was easy to loose the target.

The only time where i have problems with the focus in general when using 45pts is with swimmers in the water during daylight with sun. The sun reflecting on the water in front of the swimmer is often more contrast than the swimmer itself and can easily fool the AF.

But other than that (and besides user error) i have not had much of a problem with AF.

--
Michael Salzlechner
StarZen Digital Imaging
http://www.starzen.com/imaging

photos at http://www.salzlechner.com/photo
 
CPZ said:
Use only the center focus point and and AI servo and I think it
will eliminate most of this problem. I accidently change my
settings to all focus points once and got the same results that you
did.

Click to expand...
 
It looks to me as though the AF is tracking the ball but I have to agree with others that it appears to be focussed in front of it - perhaps it started tracking the ball when it was in the center of the picture and once it had tracked it down to the ground the switch was made to the grass.

One thing I might mention is that when the camera is held in the vertical orientation, most - and often all - of the off center sensors, particularly with long telephotos, are only vertical line sensitive (the manual says they are horizontal line sensitive only but thats with the camera in landscapre orientation). Note that the player you are wanting to track has very little contrast that gives vertical lines so if the center AF point ever got off that player the AF would want to switch to something else. The ball, OTOH, could be tracked by any sensor due to the high contrast of it's markings.

I photograph almost always in vertical orientation and have found that the AF pretty much sucks when it comes to tracking. I can't use the center point because I photograph pairs of people dancing and during most moments of interest the background is what you see in the center (between the two dancers) and vertical line contrast is rarely good so the offcenter points aren't great. The offcenter cross type points are better but I'm watching the dancers' heads and upper bodies in order to time and frame the shots, so tracking down around their waists is difficult. Naturally I never let it switch to all 45 points because then it will track the background for sure, since that never wants for contrast.

I've found single shot useless because the timing is always critical and you have little control over when the shot is actually taken, if at all.
Oliver reid said:
Here is the (uncropped) picture:



I had been tracking this player with the button half down, and
this is the first of 3 frames I shot as she broke into the penalty
area . It appears the camera decided to focus on the ball. In the
next two shots the ball was sharp and the player was soft.
e.g. (in this shot she has just passed the ball towards the camera):



My theory is that in the first shot the Af system tried to focus
on the ball and then tracked it. Then in the second shot it
decided, the ball having moved out of the AF area, the grass just
below the center of the frame was the best choice.

Here is the meta data. Any suggestions as to how to avoid this
problem would be most welcome. E.g. is AI servo really needed for a
"slow" sport like youth soccer. If not I could use one shot.

TIA. Oliver

Shooting Mode
Aperture-Priority AE
Tv(Shutter Speed)
1/1250
Av(Aperture Value)
5.6
ISO Speed
640
Lens
100.0 - 400.0mm
Focal Length
400.0mm
Image Size
2464x1648
Image Quality
RAW
White Balance
Daylight
AF Mode
AI Servo AF

11:AF point selection method
0:AF point selection button + Main (horizontal) / Quick Control
(vertical) dial operation

13:Number AF points/Spot metering
0:45/Center AF point
16:Safety shift in Av or Tv
0:Disable
17:AF point activation area
1:Expand(TTL. of 7 AF points)
18:Switch to registered AF point
1:Switch using assist button only
19:Lens AF stop button function
0:AF stop
20:AI SERVO tracking sensitivity
0:Standard
Drive Mode
High-speed continuous shooting
Click to expand...
 
If you shoot a number of pictures in a row, the focus is supposed to be correct on the 2:nd image and further on, not on the first pic. I was told it works that way when i checked my canon for focussingissues.
 
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