7D Focus Grabbed the wrong Focus

Corey Kessler · Jan 28, 2011

In the first picture (actually a series) the focus grabbed correctly. There were about 5 shots taken here.

Now, two changes here, my friend zoomed out a bit and the focus point shifted a little bit off center to the right. You'll see the Tree is in perfect focus! But the focus point almost completely covered me.

Here is a screen shot of the active focus point.

Now, Ive done some testing and have found that the camera will grab focus well above the visual focus point in the view finder. I discovered this by trying to focus on a white wall. On it I put a yellow post it note. The camera shouldn't grab focus as there is no contrast. Now, putting the focus point over the yellow postit note, it grabbed focus. Now i moved around a bit with the focus point well under (Not remotely close) the yellow note and the camera grabbed focus. On the other hand, when i reversed it and put the focus point ABOVE the yellow note, it didn't grab it even when it barely covered the yellow note on the bottom it didn't grab it.

Are the other cameras behaving this way?

It seems that it shouldn't be this sensitive.. But here is a real life example of the glitch.

riknash · Jan 28, 2011

Can you provide us with the AF and drive mode (Single/AI Focus/AI Servo) info? Was the camera in single point, spot focus or fully automatic modes? If possible, can you provide one image sample where the EXIF info hasn't been altered?

I'm guessing you might have had the camera in an automatic multipoint focus mode which can give some really bad performances unless it is understood how they are to be used.

Do understand that the focus area of any focus spot is larger than the red square.

Dewight McMullen · Jan 28, 2011

The actual sensor that detects the contrast extends beyond the box you see in the view finder and your investigation is just confirming what's in the manual. The part of the sensor that's above the box for the active point locked on to the higher contract of the tree behind you. If you sweater had more contract, I doubt that it would have locked onto the tree. Either through continued use or more experiments like the one you did will help you to better estimate the true size of the sensor. It is also important to consider the amount of contract in the area under the active focus point relative to the area outside the box because wants to lock onto whatever has the greatest amount of contrast.

Glenn_Sydney · Jan 28, 2011

Corey Kessler said:
In the first picture (actually a series) the focus grabbed correctly. There were about 5 shots taken here.

Now, two changes here, my friend zoomed out a bit and the focus point shifted a little bit off center to the right. You'll see the Tree is in perfect focus! But the focus point almost completely covered me.

Here is a screen shot of the active focus point.

Now, Ive done some testing and have found that the camera will grab focus well above the visual focus point in the view finder. I discovered this by trying to focus on a white wall. On it I put a yellow post it note. The camera shouldn't grab focus as there is no contrast. Now, putting the focus point over the yellow postit note, it grabbed focus. Now i moved around a bit with the focus point well under (Not remotely close) the yellow note and the camera grabbed focus. On the other hand, when i reversed it and put the focus point ABOVE the yellow note, it didn't grab it even when it barely covered the yellow note on the bottom it didn't grab it.

Are the other cameras behaving this way?

It seems that it shouldn't be this sensitive.. But here is a real life example of the glitch.

Your better of shooting with single point rather than multi focus points. Otherwise it can be hit and miss. If you set your camera up for it, you can easily toggle to any focus point using the joy stick. One of the advantages of the 7D is that it has many points to choose from making composition easier and avoiding the need to focus and recompose

Corey Kessler · Jan 28, 2011

It was One-Shot AF & AF Point Expansion.

There are about 10 good pictures and 10 bad. The 10 bad all line up the same. The difference is the good pictures line up more center on my body like the first picture and the second group of shots, I am not "Blocking" the sensor with my body.

In these pictures I wasn't the photographer however I set the camera to these settings. The rest, is history..

How would I post the exif data.. I thought I exported those pictures with DPP and they should have the exif data.

Corey Kessler · Jan 28, 2011

So the kicker is That is the focus point I picked with expansion. What happened is it still went well outside of the box for focus.

Adam2 · Jan 28, 2011

I think your screen shot illustrated what's happening. You indicated that the 7d was set on a single AF point with expansion. This means that the 4 AFP's surrounding your "active" AFP are also active. Moreover as other people have indicated the true size of the AFP is larger than the small box that you see within the viewfinder. As such, I suspect that either one of the assist AFP's or the active AFP grabbed the more contrasty tree/lights over your lower contrast green sweater.

Read about the 7d AF system here: http://www.canondv.com/dlc/controller?act=GetArticleAct&articleID=3049&fromTips=1

Also, the digitalpicture.com (amongst others) has an illustration of the AFP size and characteristics (look about 1/2 way down the page): http://www.the-digital-picture.com/Reviews/Canon-EOS-7D-Digital-SLR-Camera-Review.aspx

Corey Kessler said:
Here is a screen shot of the active focus point.

Flying Fish · Jan 28, 2011

It's a $1700 camera. It should focus in the focus square. I agree, the situation Corey Kessler set up isn't the easiest possible for the camera, and I can imagine it would be misfocus occasionally, but not half the time.

I have one suggestion for you to try, mainly to get more information, and that's to choose spot focus. That makes the area covered by AF point smaller. It really does do that. The downside is that sometimes there's not enough contrast in that small area and so the camera has trouble focusing. But you might learn more about what it's grabbing for focus.

I have a 7D and if I had got those results I'd be disappointed.

FF

riknash · Jan 28, 2011

Adam2 said:
I think your screen shot illustrated what's happening. You indicated that the 7d was set on a single AF point with expansion. This means that the 4 AFP's surrounding your "active" AFP are also active. Moreover as other people have indicated the true size of the AFP is larger than the small box that you see within the viewfinder. As such, I suspect that either one of the assist AFP's or the active AFP grabbed the more contrasty tree/lights over your lower contrast green sweater.

Shouldn't the transition from green sweater to v-neck skintone have provided overwelming contrast over that of the tree in the background?

Why would AF point with expansion not be a suitable focus method in this example? If true, then AF point with expansion with One-Shot AF, can never be trusted in any situation where there is any kind of contrasty background.

Doubtlessly it seems that the only reliable focus method is simple single point One-Shot AF. You can manually select any focus point, but don't let the camera choose the focus point/s.

Corey Kessler · Jan 28, 2011

With AF Point Expansion the focus point is recorded. In this case, 90% of the focus point was covered by my dull green sweater. I admit that. What I am saying is the alignment of the real sensor is much higher. In fact I would estimate more than half the the true focusing sensor is above the visual box. I have played around with this with yellow against a white wall, try it.

Now, this didn't happen once, but I have about 6 pictures all did the same thing. As the user (i'm reluctant to call my self a photographer or my friend taking the pictures) the correct focus point illuminated and one would have expected the proper focus. I mean who has time to magnify in 15x to check focus?

In this case, a zone focus may have have been the proper choice. Just not the top zone as it has a tendency to go higher than one would expect.

riknash · Jan 28, 2011

Flying Fish said:
It's a $1700 camera. It should focus in the focus square. I agree, the situation Corey Kessler set up isn't the easiest possible for the camera, and I can imagine it would be misfocus occasionally, but not half the time.

I disagree that Corey's setup was all that difficult. There are lots of contrast rich subjects in front of the AF point like his neck and his eyeglasses.

What might have happened is that the person taking the photo inadvertently performed a focus and recompose. They may have half-pressed the shutter and got the beep, then composed the red square on Corey and then tripped the shutter.

Flying Fish said:
I have one suggestion for you to try, mainly to get more information, and that's to choose spot focus. That makes the area covered by AF point smaller. It really does do that. The downside is that sometimes there's not enough contrast in that small area and so the camera has trouble focusing. But you might learn more about what it's grabbing for focus.

I have a 7D and if I had got those results I'd be disappointed.

I wouldn't recommend the spot AF specifically for the reason you described. Easy to have the spot on a poor contrast area or shooting through the subjects at something in the background. Don't forget, the OP has handed the camera to someone to use to frame and press the shutter button. He needs to give that person the best chance of getting it right. Spot AF wouldn't be a safe choice. If I was going to hand the camera to someone else, I would set it to single point One-Shot with the AF point selected that would best be on one of the center subject's face and eyes. Instruct them where to place the red square and half depress the shutter to focus, hear the beep and fully depress the shutter.

Corey Kessler · Jan 28, 2011

The series of pictures were all shot, about 10 of them in less than 2 mins. Doubt the focus and recompose was possible, and all of the shots grabbed the tree.

I did exactly as you said, set the camera to the best focus point. I enabled expansion to help out a bit. He zoomed out and suddenly the scene changed enough that the camera said, hey that tree has more contrast lets focus on it.

It is an alignment thing. I guess I should be talking to canon to see if it is way out of spec. Has anyone tried the contrasty subject against a white wall to see how your camera aligns with the visual squares?

riknash · Jan 28, 2011

Corey Kessler said:
With AF Point Expansion the focus point is recorded. In this case, 90% of the focus point was covered by my dull green sweater. I admit that. What I am saying is the alignment of the real sensor is much higher. In fact I would estimate more than half the the true focusing sensor is above the visual box. I have played around with this with yellow against a white wall, try it.

Ok I have tried it but don't quite understand what I should be observing.

Corey Kessler said:
Now, this didn't happen once, but I have about 6 pictures all did the same thing. As the user (i'm reluctant to call my self a photographer or my friend taking the pictures) the correct focus point illuminated and one would have expected the proper focus. I mean who has time to magnify in 15x to check focus?

In this case, a zone focus may have have been the proper choice. Just not the top zone as it has a tendency to go higher than one would expect.

riknash · Jan 28, 2011

Corey Kessler said:
The series of pictures were all shot, about 10 of them in less than 2 mins. Doubt the focus and recompose was possible, and all of the shots grabbed the tree.

I did exactly as you said, set the camera to the best focus point. I enabled expansion to help out a bit. He zoomed out and suddenly the scene changed enough that the camera said, hey that tree has more contrast lets focus on it.

Don't trust the camera's auto AF point expansion selection. I'm thinking that maybe those tree lights are super contrasty and that's why the silly AF expansion jumped over to the light bulbs..

Corey Kessler said:
It is an alignment thing. I guess I should be talking to canon to see if it is way out of spec. Has anyone tried the contrasty subject against a white wall to see how your camera aligns with the visual squares?

Corey Kessler · Jan 28, 2011

Here. I picked the spot as shown below. Without focus and recomposing I am able to get a focus lock as seen below. It is so far off the contrast is actually in the focus point above it. Now, granted this test was performed in junk light and I will see if the camera behaves the same during daylight.

riknash · Jan 28, 2011

I understand your test now. I did basically the same thing. If you look at my photo where the yellow card is above the center focus point, observe that the AF point above the center AF point is red. That would suggest that the center point saw the card and immediately passed it over to the AF point above it in order to obtain a better focus. I cannot get it to AF if I move the center AF point any further below the yellow card. When above the card, it is even harder to get the AF to start focusing if the center AF point is not on the edge of the card. Am I clear with my explanation?

Corey Kessler said:
Here. I picked the spot as shown below. Without focus and recomposing I am able to get a focus lock as seen below. It is so far off the contrast is actually in the focus point above it. Now, granted this test was performed in junk light and I will see if the camera behaves the same during daylight.

Corey Kessler · Jan 28, 2011

Yes, you're on the right track. Now, disable expansion and move the focus point off the the center up one click and see if you can get it to focus as mine did, by placing it below the yellow card. And then a little bit lower.

riknash · Jan 28, 2011

Corey Kessler said:
Yes, you're on the right track. Now, disable expansion and move the focus point off the the center up one click and see if you can get it to focus as mine did, by placing it below the yellow card. And then a little bit lower.

All right. I took it out of AF point expansion and determined where the farthest point away from the yellow card that the AF would focus. (First two photos, bottom and top of card). Third photo is same thing but I manually selected the AF point above the center AF point.

Speedchaser · Jan 28, 2011

I've exactly the same issue as Corey Kessler. Using AF Point expansion, the 7D grabbed the wrong focus. It's on focus if I use Zone AF.

Using AF Point Expansion - RAW Coverted to JPG with DPP

Using Zone AF - RAW Coverted to JPG with DPP

There's a post in Flickr about the same issue here.
http://www.flickr.com/groups/canon_7d_digital_slr/discuss/72157623960222545/

--
Seeking to Understand, Rather to Be Understood.

Zeee · Jan 28, 2011

OK. I have a question. This is out of the manual. I can be completely off track (no pun intended) but here it goes.

The manuals instructions.

The manually –selected AF point and adjacent points are used to focus. Effective when it is difficult to track a moving subject with just one AF point.

With AI Servo, the manually – selected AF point must focus track the subject first. However it is easier to focus the target subject than with Zone AF.

With one shot AF, when focus is achieved the expanded AF point, the expanded AF point will also be displayed along with the manually selected AF point.

Anyone see a second red square?

The first sentence clearly states "tracking a moving subject". My question. What are we "tracking" in these stills? Would not just turning off the expansion be easier to work with shooting a still. Seems like expansion was designed for tracking a moving subject.

--
When things go too smoothly it's life's way of throwing you off balance.

7D Focus Grabbed the wrong Focus

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