AI Focus miss-focus sample

[Frank B]

On another thread the statement was made that no one has provided evidence that AI Focus has been fooled. I have a 10D and AI Focus works most of the time, but not all the time. The other day I went out and did a quick test. I used AI Focus Mode, with the center focus point only enabled. I focused on the telephone pole and half pressed the shutter to hold focus and recomposed. In this picture the camera shifted from Single to Servo focus with the result that the telephone pole is out of focus.

This is not to criticize the 300D which allows only AI Focus in its creative modes. It is simply to confirm that when using this mode (at least on my 10D) and recomposing there is a risk on occasion of a picture being out of focus due to the camera mistakenly switching from Single to Servo Focus



Frank B

.

 

[Mark Marshall]

Hi Frank - how fast did you swing it over? Were you simulating some lateral action shot? - m²

On another thread the statement was made that no one has provided
evidence that AI Focus has been fooled. I have a 10D and AI Focus
works most of the time, but not all the time. The other day I went
out and did a quick test. I used AI Focus Mode, with the center
focus point only enabled. I focused on the telephone pole and half
pressed the shutter to hold focus and recomposed. In this picture
the camera shifted from Single to Servo focus with the result that
the telephone pole is out of focus.

This is not to criticize the 300D which allows only AI Focus in its
creative modes. It is simply to confirm that when using this mode
(at least on my 10D) and recomposing there is a risk on occasion of
a picture being out of focus due to the camera mistakenly switching
from Single to Servo Focus



Frank B

.

 

[Rob Patterson]

Was the wind blowing? It appears that the only thing in focus in this shot is the tree leaves. Servo focus isn't supposed to kick in until something moves. Those leaves wouldn't be moving towards the camera or away from the camera. That's the only time servo focus is supposed to kick in. Blowing leaves is minimal movement. This doesn't look good to me.

 

[DavidP #28649]

Presuambly it doesn't do this all the time. Otherwise Phil (and others) would've had similar results.

How often does it occur, would you say?

And any idea of what causes it? Why only some shots? There's probably a reason, though figuring it out is another thing altogether.

My guess (in this case) might be that the trees (the "new subject" after recomposing) began to blow a bit (moving toward and away from the camera), and the camera picked this up as movement, and kicked in the AI-Servo.

Which would beg the question: If you'd selected all seven AF points, locked on with the center one, then recomposed, would the fact that you had all seven points going (instead of just one) let the camera know that the telephone pole (which would now be under another sensor) wasn't moving, so AI-Servo didn't kick in?

Maybe in AI-Focus mode, you should really be using all seven points?

On another thread the statement was made that no one has provided
evidence that AI Focus has been fooled. I have a 10D and AI Focus
works most of the time, but not all the time. The other day I went
out and did a quick test. I used AI Focus Mode, with the center
focus point only enabled. I focused on the telephone pole and half
pressed the shutter to hold focus and recomposed. In this picture
the camera shifted from Single to Servo focus with the result that
the telephone pole is out of focus.

This is not to criticize the 300D which allows only AI Focus in its
creative modes. It is simply to confirm that when using this mode
(at least on my 10D) and recomposing there is a risk on occasion of
a picture being out of focus due to the camera mistakenly switching
from Single to Servo Focus

--
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

 

[Dzung Pham]

This is a different problem from what other people seemed to be describing. I had not heard about the camera completely refocussing on the wrong subject, I just thought that the AI Focus created additional lag where the AI Servo kicked in. In this picture, the point of focus looks to be exactly the center point so maybe the camera just completely refocused.

Did you notice any additional lag?

On another thread the statement was made that no one has provided
evidence that AI Focus has been fooled. I have a 10D and AI Focus
works most of the time, but not all the time. The other day I went
out and did a quick test. I used AI Focus Mode, with the center
focus point only enabled. I focused on the telephone pole and half
pressed the shutter to hold focus and recomposed. In this picture
the camera shifted from Single to Servo focus with the result that
the telephone pole is out of focus.

This is not to criticize the 300D which allows only AI Focus in its
creative modes. It is simply to confirm that when using this mode
(at least on my 10D) and recomposing there is a risk on occasion of
a picture being out of focus due to the camera mistakenly switching
from Single to Servo Focus



Frank B

.

 

[DavidP #28649]

Quite a few have claimed this "refocusing problem". But others have said that they don't see this problem.

So the question is, WHY do some see it, and not others?

Perhaps if this happens it means that the camera is defective and needs a tweak? Or perhaps there are certain conditions that will cause all cameras to do this, and those who haven't seen the problem just haven't encountered those conditions.

In the latter case, knowing what those condition are is something that we'd all benefit in knowing.

This is a different problem from what other people seemed to be
describing. I had not heard about the camera completely
refocussing on the wrong subject,

--
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

 

[Mark Marshall]

True - you moved the center focus point to a nearer object, in essence telling the camera distance has indeed changed. - m²

Did you notice any additional lag?

On another thread the statement was made that no one has provided
evidence that AI Focus has been fooled. I have a 10D and AI Focus
works most of the time, but not all the time. The other day I went
out and did a quick test. I used AI Focus Mode, with the center
focus point only enabled. I focused on the telephone pole and half
pressed the shutter to hold focus and recomposed. In this picture
the camera shifted from Single to Servo focus with the result that
the telephone pole is out of focus.

This is not to criticize the 300D which allows only AI Focus in its
creative modes. It is simply to confirm that when using this mode
(at least on my 10D) and recomposing there is a risk on occasion of
a picture being out of focus due to the camera mistakenly switching
from Single to Servo Focus



Frank B

.

 

[Frank B]

To be fair I don't think it will happen too often. In the "test" the shutter speed was 125 with IS shut off and the the focal length 135mm. So there could be some camera shake. However, the AI Focus definitely switched. I could here and see the camera refocusing. I don't remember if it was especially windy. I may well have moved the camera faster than I would normally to recompose, so it may not be a fair test.

I went out today and tried again. The following is another example. I focused on the corner of the red garage to the right and then recomposed. The camera switched to servo mode. This was taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had to try 3 or 4 times before it switched.



I tried AIFocus in my "real" photography only once and in that outdoor session I remember being somewhat dissatisfied with the focus on one or two pictures and stopped using it. I was not sure if the lack of good focus was due to the AIFocus, but figured why take the chance in the future.

Of course It could be that my 10D is particularly bad and/or that the 300D will be better.

Frank B

 

[DavidP #28649]

Others have shown examples, though, where they recomposed, putting the AF sensor on another subject (further away in this case), and the camera did NOT decide to go into AI-Servo and change the focus distance.

True - you moved the center focus point to a nearer object, in
essence telling the camera distance has indeed changed. - m²

--
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

 

[DavidP #28649]

This is very similar to a set of shots posted by somebody the other day, where he showd that the AI-Focus did NOT switch to AI-Servo mode and refocus after recomposition.

And here, your "new subject" is further away than what you initiailly focused on (just like his example), and there's no danger of that tree moving to induce AI-Servo, either.

One difference between your shots and his that stand out in my mind: his "new subject" (after recomposing) was a lot further away than the intended subject. In your examples, the "new subject" was relatively close to the intended subject.

This is also true (I think) of the guy who was having problems with this during weddings.

If so, my hypothesis at this point is: if you recompose and the AF sensor is placed over a "near object", the auto-focus logic will interpret that as movement and re-focus. If you recompose and the AF sensor is placed over a "far object", the auto-focus logic will interpret that as no movement at all. Or simply realize that it can't track an object moving that fast.

To be fair I don't think it will happen too often. In the "test"
the shutter speed was 125 with IS shut off and the the focal length
135mm. So there could be some camera shake. However, the AI Focus
definitely switched. I could here and see the camera refocusing.
I don't remember if it was especially windy. I may well have moved
the camera faster than I would normally to recompose, so it may not
be a fair test.

I went out today and tried again. The following is another
example. I focused on the corner of the red garage to the right
and then recomposed. The camera switched to servo mode. This was
taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had
to try 3 or 4 times before it switched.



I tried AIFocus in my "real" photography only once and in that
outdoor session I remember being somewhat dissatisfied with the
focus on one or two pictures and stopped using it. I was not sure
if the lack of good focus was due to the AIFocus, but figured why
take the chance in the future.

Of course It could be that my 10D is particularly bad and/or that
the 300D will be better.

Frank B

--
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

 

[Ulysses]

What lens are you using?

And how are you verifying that it has switched to AI Servo? By the EXIF data?

--

Ulysses

 

[DavidP #28649]

I think he's just looking through the lens and seeing that the camera refocuses. And he can hear the lens focusing, too. Even with USM lenses, you can hear the focus going back and forth in AI-Servo mode if you listen carefully. It's VERY easy to hear on a lens like the 85/1.2

And how are you verifying that it has switched to AI Servo? By the
EXIF data?

--
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

 

[cx532]

This will only happen if something under the active focus point and at the exact 'locked' focus distance starts to move away from or toward the camera.

In the first case, you locked focus on the pole then recomposed the shot. The active focus point was then over the leaves on the tree, which were moving in the wind, and as they move, were at times the exact same distance from the camera as the original focus point, the pole. All the the camera saw was something at the focus point start to move so switched to track the object, ie the leaves.

In the second case, the focus point probably passed over the edge of the tree, which is the same distance as the garage and started tracking as the focus point moved further across the tree. The tree isn't moving, the camera is, but to the camera, there's no difference.

AI Focus is actually pretty clever, but like everything 'automatic', can occaisionally be fooled.

David

To be fair I don't think it will happen too often. In the "test"
the shutter speed was 125 with IS shut off and the the focal length
135mm. So there could be some camera shake. However, the AI Focus
definitely switched. I could here and see the camera refocusing.
I don't remember if it was especially windy. I may well have moved
the camera faster than I would normally to recompose, so it may not
be a fair test.

I went out today and tried again. The following is another
example. I focused on the corner of the red garage to the right
and then recomposed. The camera switched to servo mode. This was
taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had
to try 3 or 4 times before it switched.



I tried AIFocus in my "real" photography only once and in that
outdoor session I remember being somewhat dissatisfied with the
focus on one or two pictures and stopped using it. I was not sure
if the lack of good focus was due to the AIFocus, but figured why
take the chance in the future.

Of course It could be that my 10D is particularly bad and/or that
the 300D will be better.

Frank B

 

[Frank B]

I used a 28-135IS with IS shut off. I could here the servo start to work and see the refocusing. I don't think the EXIF will show a switch only that the focus mode was AI Focus.

Frank B

What lens are you using?

And how are you verifying that it has switched to AI Servo? By the
EXIF data?

--

Ulysses

 

[Frank B]

In this case I focused on the tree and then refocused on the corner of the garage.



Maybe my AI focus is defective?

Frank B

 

[Frank B]

I don't think that is the reason. In the first picture the distance from the tree to the post is about 30 feet. The 135mm (216mm 35mm equivalent) focal length makes the tree and the pole look closer then they are.

Frank B

In the first case, you locked focus on the pole then recomposed the
shot. The active focus point was then over the leaves on the tree,
which were moving in the wind, and as they move, were at times the
exact same distance from the camera as the original focus point,
the pole. All the the camera saw was something at the focus point
start to move so switched to track the object, ie the leaves.

In the second case, the focus point probably passed over the edge
of the tree, which is the same distance as the garage and started
tracking as the focus point moved further across the tree. The tree
isn't moving, the camera is, but to the camera, there's no
difference.

AI Focus is actually pretty clever, but like everything
'automatic', can occaisionally be fooled.

David

To be fair I don't think it will happen too often. In the "test"
the shutter speed was 125 with IS shut off and the the focal length
135mm. So there could be some camera shake. However, the AI Focus
definitely switched. I could here and see the camera refocusing.
I don't remember if it was especially windy. I may well have moved
the camera faster than I would normally to recompose, so it may not
be a fair test.

I went out today and tried again. The following is another
example. I focused on the corner of the red garage to the right
and then recomposed. The camera switched to servo mode. This was
taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had
to try 3 or 4 times before it switched.



I tried AIFocus in my "real" photography only once and in that
outdoor session I remember being somewhat dissatisfied with the
focus on one or two pictures and stopped using it. I was not sure
if the lack of good focus was due to the AIFocus, but figured why
take the chance in the future.

Of course It could be that my 10D is particularly bad and/or that
the 300D will be better.

Frank B

 

[Justme]

nt

In this case I focused on the tree and then refocused on the corner
of the garage.



Maybe my AI focus is defective?

Frank B

 

[Mark Marshall]

I dunno Frank - I read it a little different. The camera does have a processor in it, if after 3 or 4 times at the same sampling you haven't got what you want maybe it just gave up and dialed in the tree to make you happy ;-) - m²

I went out today and tried again. The following is another
example. I focused on the corner of the red garage to the right
and then recomposed. The camera switched to servo mode. This was
taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had
to try 3 or 4 times before it switched.

 

[cx532]

Hmmm - I looked again - The tree does look closer. My description is right as I understand AI-focus mode is supposed to work, so I'm not sure what happened with that one.

Try this as an experiment. Stand 10 feet or so from a open doorway with an assistant 10 feet the other side. Set the camera to AI-focus, select centre focus point and get a focus lock on the door frame. Then aim at your assistant, and get them to walk through the doorway, all the time holding the shuuter half pressed. AI-focus should completely ignore them until they actually pass through the doorway, when it should switch modes and start tracking.

Now do the same thing but with 'auto focus point selection' and keep the active focus point over the door frame. AI-focus should completely ignore your assistant even if another (non active) focus point is over them as they pass through the doorway.

If anything else happens, your camera is faulty!

David

Frank B

In the first case, you locked focus on the pole then recomposed the
shot. The active focus point was then over the leaves on the tree,
which were moving in the wind, and as they move, were at times the
exact same distance from the camera as the original focus point,
the pole. All the the camera saw was something at the focus point
start to move so switched to track the object, ie the leaves.

In the second case, the focus point probably passed over the edge
of the tree, which is the same distance as the garage and started
tracking as the focus point moved further across the tree. The tree
isn't moving, the camera is, but to the camera, there's no
difference.

AI Focus is actually pretty clever, but like everything
'automatic', can occaisionally be fooled.

David

To be fair I don't think it will happen too often. In the "test"
the shutter speed was 125 with IS shut off and the the focal length
135mm. So there could be some camera shake. However, the AI Focus
definitely switched. I could here and see the camera refocusing.
I don't remember if it was especially windy. I may well have moved
the camera faster than I would normally to recompose, so it may not
be a fair test.

I went out today and tried again. The following is another
example. I focused on the corner of the red garage to the right
and then recomposed. The camera switched to servo mode. This was
taken at 1/250 at 53mm, f4.3 and I recomposed slowly. I only had
to try 3 or 4 times before it switched.



I tried AIFocus in my "real" photography only once and in that
outdoor session I remember being somewhat dissatisfied with the
focus on one or two pictures and stopped using it. I was not sure
if the lack of good focus was due to the AIFocus, but figured why
take the chance in the future.

Of course It could be that my 10D is particularly bad and/or that
the 300D will be better.

Frank B

 

[Rob Patterson]

Others have shown examples, though, where they recomposed, putting
the AF sensor on another subject (further away in this case), and
the camera did NOT decide to go into AI-Servo and change the focus
distance.

........to a moving object. This has been one of the big problems with the 10D. The cure with the 10d is to turn the servo focus function off. This is not possible with this camera.

If those tree limbs were blowing in the wind then the autofocus spot one picked (telephone pole, street background, street foreground) would be overridden and the servo focus would refocus on the moving object. In this case it'd be the limbs of that tree blowing in the wind.

I don't think the servo focus should kick in on those moving limbs. Were they moving? If so then that servo focus could cause problems. Maybe someone else figured this out further down this thread. I'll keep reading.

True - you moved the center focus point to a nearer object, in
essence telling the camera distance has indeed changed. - m²

--
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