7D 19 point autofocus - what's the point?

[strictfunctor]

My 2c would be that for any static scene, eg a landscape, manual focus can always
beat any autofocus system, but in a dynamic situation, AF will win, and AF with more
points will be better than AF with fewer.

[arthurking83]

pmack, I think you don't have a full understanding of how the focusing system works.
I think you have a basic understanding, of it, but if you expect the camera to focus on a particular on a scene like that and in a consistent manner... well you've just figured out for yourself that you have less understanding of the camera's mode of operation. You just have yet to fully realise this fact.

First up!!... your mode of testing is totally flawed because you haven't given us a reference image to show what the lens is capable of producing at f/4. That is, have you taken a similar image at f/4 focsed to a similar distance to show us(and yourself) that the lens is capable of producing sharp image into the corner at f/4?
You then completely ignore Andrew's(I@M) comments that the image not in focus must be in focus somewhere, and argue your point without fully realising the consequences of the test.
You say that no point is in focus, but don't offer any alternative explanations(such as soft corners due to wide open aperture). You haven't offered any clue as to what lens either. Is it a kit lens? Is it a pro L lens with known fabulous across the frame sharpness. Is it an f/1.4 or f/1.8 lens shot at f/4.. more likely to be sharp across the frame, than an f/4 lens.
Is it a zoom lens shot at the longest focal length.. known to be softer in the corners than it would otherwise be at the shorter end of the focal range?

You're replies to others help are usually counter productive to your quest of working out how to best utilise the auto point focusing mode on this camera, and due to that the inevitable consequence is that you are doomed never to figure this out. Simple solution is to drop it and stop banging your head against some brick wall of technical mystery.. OR!!!! open your mind a little, stop arguing against other's helpful replies and do the test in a more methodical manner.. not some higgledy piggeldy botch job.. you get nowhere this way.

Zolaxi basically explained exactly what I was going to initially comment too.. the camera doesn't read human thought. While you know what you want, the camera only knows what to do as it's programming allows it to do.. no more.

Quick hint. Try the non focused test image again at something like f/8(not knowing what lens you've used) and see if any part of the scene is rendered sharper.(if you say that it's front focused in that scene, then there should be something in focus). Does the lens have a distance scale? If so, before you change any setting, at least have a peek at the distance scale and confirm that the lens has focused to a specific distance
Having done that in the first place, and given that data, I wouldn't have replied at all to your thread, as it would have implied that you have some idea on the technical aspect on what you're trying to achieve.

As it stands, all you have confirmed is that you have limited understanding of the process of testing on a technical level.

OK!! and whoops on my part! I initially made this reply having read a good part of this thread,and then skimmed and missed a few of the final few replies. It seems you have given us the info as to the lens.. and quite simply not surprising!! an F/4 lens shot wide open at the longest focal length.. can you see the error in your testing method. Did you really expect there to be the same image sharpness across the entire frame? Do you know that this lens has an entirely flat focus plane, or is there some curvature?

Your best bet is to either trash all the data you have gathered already, forget that you have this prejudice against this auto point focusing mode and start all over again with an open mind. If you don't, your tainted opinion of this mode of the camera's feature will lead you to see faults where faults probably don't exist.

[agb]

Have another read of this if you have not already done so.
http://www.usa.canon.com/uploadedima...QuickGuide.pdf

[pmack]

pmack, I think you don't have a full understanding of how the focusing system works.
I think you have a basic understanding, of it, but if you expect the camera to focus on a particular on a scene like that and in a consistent manner... well you've just figured out for yourself that you have less understanding of the camera's mode of operation. You just have yet to fully realise this fact.

Well no I certainly do not have a full understanding of how the focus system works as I am not one of the engineers who designed it. And I don't hesitate to say that there are likely very few people on this forum that do. At least certainly none who have posted in this thread so far. Yes I have read most material (and yes have RTFM) that canon have released, as have a lot of you.

I expect the camera to focus on the image that it tells the user. It's not hard to understand. This testing has simply shown me a weakness in one function of the autofocus system, nothing more.

First up!!... your mode of testing is totally flawed because you haven't given us a reference image to show what the lens is capable of producing at f/4. That is, have you taken a similar image at f/4 focsed to a similar distance to show us(and yourself) that the lens is capable of producing sharp image into the corner at f/4?

Excuse me? Did you actually look at the original post which has the same image in focus, at f/4?
And why on earth are you overcomplicating things and now talking about corner sharpness? This post of mine was so amazingly straight forward, yet I get people like you trying to prove my lack of understanding, and then bring up completely irrelevant points.

You then completely ignore Andrew's(I@M) comments that the image not in focus must be in focus somewhere, and argue your point without fully realising the consequences of the test.
You say that no point is in focus, but don't offer any alternative explanations(such as soft corners due to wide open aperture). You haven't offered any clue as to what lens either. Is it a kit lens? Is it a pro L lens with known fabulous across the frame sharpness. Is it an f/1.4 or f/1.8 lens shot at f/4.. more likely to be sharp across the frame, than an f/4 lens.
Is it a zoom lens shot at the longest focal length.. known to be softer in the corners than it would otherwise be at the shorter end of the focal range?

Ah no I did not completely ignore any of Andrews comments, I believe I addressed everything he said. Argue the point without realising the consequence? Sorry not sure what you are getting at with that, it was pretty self explanatory what was being talked about, it was simply a trivial misunderstanding of my explanation of how the lens focused to a plane in front of the photographed scene. Once again, corner sharpness? Why are you bringing up useless points. It as shot wide open to exaggerate any missed focus. Pic #1 @ f4 has nothing visible in focus. Pic # 2 @ f/4 has the entire hill in acceptable focus. I can't see how that is hard to follow.
And yep as you're realised, I've posted details of my shots, and the lens was a canon 24-105L lens.

You're replies to others help are usually counter productive to your quest of working out how to best utilise the auto point focusing mode on this camera, and due to that the inevitable consequence is that you are doomed never to figure this out. Simple solution is to drop it and stop banging your head against some brick wall of technical mystery.. OR!!!! open your mind a little, stop arguing against other's helpful replies and do the test in a more methodical manner.. not some higgledy piggeldy botch job.. you get nowhere this way.

People (like yourself) think they are being useful by telling me to read the manual, as though I don't have a good understanding of how to use the autofocus system. Well I believe I do have a reasonably good understanding (not full) of this camera, and I don't think anyone one has posted anything in this thread that I did not already know. The only reason I am doomed to figure this out (on this forum) is that there are so many people in this internet age full of knowledge, but without the intelligence to realise their knowledge is irrelevant, or simply wrong.

And I have done other methodical tests, and the camera has worked. The reason I have posted these particular results are because it is in this particular scenario (multipoint AF at an entire scene close to infinity), that a weakness of the camera is revealed. All I am doing is testing how reliable the camera is in that situation, and the results are repeat-ably POOR. Fact.

[MarkChap]

What make/model is your tripod, I am still of the thought that the first image particularly is affected by camera shake, not just simply being out of focus.

If the camera has front focused to a point close enough to the camera, to not be able to render anything in that scene sharp, there is definitely a serious issue with the AF system. If it was that bad, it would not render anything sharp, ever.

[pmack]

Zolaxi basically explained exactly what I was going to initially comment too.. the camera doesn't read human thought. While you know what you want, the camera only knows what to do as it's programming allows it to do.. no more.

Did you bother reading my response to Zolaxi's post? The camera should not need to mind read in this situation. I'll post my reply again:
“The camera should not have to read the operators mind to focus in the image i've shown.
I don't care which square it chooses to select to focus on in this case. (as all squares cover a region within the available depth of field at this distance)
It claims that it made focus on about 7 focus points, but in reality, the entire image is out of focus as it has focused on a plane in front of the photographed scene.
how hard is this to understand? ”

Quick hint. Try the non focused test image again at something like f/8(not knowing what lens you've used) and see if any part of the scene is rendered sharper.(if you say that it's front focused in that scene, then there should be something in focus). Does the lens have a distance scale? If so, before you change any setting, at least have a peek at the distance scale and confirm that the lens has focused to a specific distance
Having done that in the first place, and given that data, I wouldn't have replied at all to your thread, as it would have implied that you have some idea on the technical aspect on what you're trying to achieve.

Well I'm sorry, next time I start a thread I will state that I graduated from my mechanical engineering degree with honours and have a solid understanding of the technical aspects of photography, due to fact I am more passionate about photography that I am with designing...

And of course the image will be sharper at f/8. I walked out to my balcony just now and took the image again at f/4 and f/8. The result at f/8 with 19 point auto select, was very similar to the result at f/4 with center point autofocus. As expected. That was a good suggestion about looking at the distance scale however, as it showed me that the error is only marginal (at least from observing the scale). When it gets the focus correct (with the center point), the mark on the lens is just shy of infinity. In Auto select, it moves approximately 0.5mm away from infinity. A very fine adjustment, but obviously noticeable at f/4. So I according to the scale and the results, I would approximate that when in 19 point Auto select, it is focusing approximately 200 meters or more short of the scene which is approximately 500 meters away.

As it stands, all you have confirmed is that you have limited understanding of the process of testing on a technical level.

And how might that be so, all I am testing is the accuracy of the auto focus in 19 point Auto select mode when taking a photo of an image close to infinity. I think you have limited understanding of what this topic is actually about.

OK!! and whoops on my part! I initially made this reply having read a good part of this thread,and then skimmed and missed a few of the final few replies. It seems you have given us the info as to the lens.. and quite simply not surprising!! an F/4 lens shot wide open at the longest focal length.. can you see the error in your testing method. Did you really expect there to be the same image sharpness across the entire frame? Do you know that this lens has an entirely flat focus plane, or is there some curvature?

Once again I think you have limited understanding of what this thread is about. Corner sharpness and the wide aperture have very little to do with what I am talking about. The wide aperture was used to help illustrate the differences in focus results. When focuses correctly at f/4, the image is acceptable. It seems you missed the photos in my original post.

Your best bet is to either trash all the data you have gathered already, forget that you have this prejudice against this auto point focusing mode and start all over again with an open mind. If you don't, your tainted opinion of this mode of the camera's feature will lead you to see faults where faults probably don't exist.

Look as canon tell users that the center/single point is more accurate, I suppose i can just accept that and not ever use Multi point due to it being largely innaccurate. I simply expected it to be more accurate than it is, but clearly that is not the case. I suspect it is largely due to the fact that probability works against you with the design of this system (the 13.5% number from my first post)

[pmack]

What make/model is your tripod, I am still of the thought that the first image particularly is affected by camera shake, not just simply being out of focus.

If the camera has front focused to a point close enough to the camera, to not be able to render anything in that scene sharp, there is definitely a serious issue with the AF system. If it was that bad, it would not render anything sharp, ever.

nope it's definetly not the tripod, i can repeat this test as often as i want, with or without tripod.
The only reason why nothing is sharp in the scene is because the middle ground is large and empty!

I did this little test, i focused to the right at the hill in 19 point auto select, locked the focus, then i moved my camera to the left towards a crane, and took the photo.
By a matter of coincidence, the crane is approximately at the distance where the lens is focused at, as this image shows:

100% crop


As you can see even though the focus was locked when the crane was out of view, that is still the rough distance it has focused the lens at.

Meaning it is actually focussing even closer than i thought (the crane is only 200 meters away from me)

[pmack]

Just to throw a spanner in the works, i did some testing with the lens @ 24mm.

In auto point select, almost all focus points lit up for this photo.
After taking the photo, i looked at the scale, it selected a distance of 3 meters! despite the closest object being about 40 meters away (trees on the bottom)



When i changed it to single/center point focus, and aimed it at the crane, it improved only slightly to a distance of 5 meters, so the shot was still out of focus.
My 10-22mm lens doesn't seem to have trouble getting an infinity focus at 10mm, not sure why the 24-105L can't get an infinity focus zoomed out.

[etherial]

Depth of Field for 24mm, f4 40m is infinite so if it isn't sharp then, you have other issues.

[MarkChap]

so if your 10-22mm acquires focus ok, maybe, just maybe, here is a thought, wait for it.

Maybe it is the lens and not the camera after all. I am sure some one suggested this very thing to early on.

You have spent the last day or say telling us with out doubt that the camera is at fault, you now say that one lens is good and one is not, so just stop and think for a minute, which part of this equation is wrong.

I still think your methodology is flawed, for the life of my I cannot work out how you can focus on something, move your camera and then claim that the camera didn't focus correctly.
And despite your claim that your tripod cannot be at fault, I am still not convinced that you haven't got blur from movement

[Art Vandelay]

Look as canon tell users that the center/single point is more accurate, I suppose i can just accept that and not ever use Multi point due to it being largely innaccurate. I simply expected it to be more accurate than it is, but clearly that is not the case. I suspect it is largely due to the fact that probability works against you with the design of this system (the 13.5% number from my first post)

I'm having a lazy sunday afternoon so turned my auto multi point selection on and poked it out the front yard. I found it worked awesomely well in that it did exactly as it's supposed to do i.e pick up and use the closest point/s it grabs.





Even in this jumble of signs and objects it still picked out the closest object.



It's not often I go birding with the 17-55, but this Ibis flew over so grabbed a shot. It picked up reasonably well considering it was a random in single shot mode, not tracked in servo.



So the multi point on the 7D itself works as intended. (Which is why most people dont use it and prefer to pick their own point of focus) It maybe time to send yours back if you keep having trouble and have exhausted all other causes.

[pmack]

so if your 10-22mm acquires focus ok, maybe, just maybe, here is a thought, wait for it.

Maybe it is the lens and not the camera after all. I am sure some one suggested this very thing to early on.

You have spent the last day or say telling us with out doubt that the camera is at fault, you now say that one lens is good and one is not, so just stop and think for a minute, which part of this equation is wrong.

The lens focuses fine when the camera uses a single auto focus point @ 105mm. This suggests to me the lens is OK. Just because the camera appears to operate well with one lens, and not so well with another lens, does not mean the lens is at fault. However if I test another copy of the 24-105L on my 7D, and it works better, then yes you could conclude that. Unfortunately I do not have another copy of this lens. Or if someone else with this lens tells me that my lens is not acting as theirs does, then that too would help me conclude that.

I still think your methodology is flawed, for the life of my I cannot work out how you can focus on something, move your camera and then claim that the camera didn't focus correctly.

Heaven forbid your life never depends on the understanding of something so simple.
I recomposed to illustrate where the focal plane actually was (approximately)
This was the photo where I obtained the focus using 19 point auto select:



Then maintaining the same focus, i moved slightly to the left (notice some of the same houses), and took this photo:



If the houses were in focus in the first photo, they would also have been in focus in the second photo. If you don't understand that, i give up.

And despite your claim that your tripod cannot be at fault, I am still not convinced that you haven't got blur from movement

Ok I hope you are just trying to frustrate me, and are not honestly still thinking this. Do you own tripods with built in vibrators or something? I'm not going to answer this, i have already explained why this has NOTHING to do with motion blur...

[pmack]

I'm having a lazy sunday afternoon so turned my auto multi point selection on and poked it out the front yard. I found it worked awesomely well in that it did exactly as it's supposed to do i.e pick up and use the closest point/s it grabs.

Hey Art thanks for testing that. My camera and lens would most likely have performed just as yours seems to have, as it does seem to work for objects reasonably close. It just seems to be when the whole scene is close to infinity that it front focuses at this focal length, like the photos i've posted.
What lens did you use by the way?

[kiwi]

I'm glad the crane was approximately at the same focal length and that you also focus and recomposed....this sort of exact testing is most comforting.

[MarkChap]

I am going to say this ONE more time, if your 10-22 focuses as expected and your 24-105 does not focus as expected, how in blue blazes can you blame the CAMERA

And for your information Tripod quality and stability has everything to do with blur. The one other constant you seem reluctant to reveal is the make and model of said rock solid tripod ??
I look at the images and I see blur, not just out of focus images, for my benefit what tripod are you using, then I can be confident that either I am on the right track or not, you want help, with out ALL of the information that is very hard

[pmack]

I'm glad the crane was approximately at the same focal length and that you also focus and recomposed....this sort of exact testing is most comforting.

I did that to illustrate a point that would be impossible to show any other way (unless i had controll of the crane and could have rotated it for the second photo.)
It was in no way meant to be any sort of exact test.

But thanks for your second usefull post in this topic that once again shows your great level of intelligence and insight.
I look forward to the third...

[ricktas]

I am closing this thread:

The OP seems to have no interest in reading the replies that could be of benefit, and seems to want to only argue with each poster about the information they are providing. Some posts by members are bordering on baiting others, which breaches site rules.