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Thread started 17 Nov 2014 (Monday) 09:47
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7D2, 1Dx, 5D3 Owners- How to make AF system work better for you

 
apersson850
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Nov 18, 2014 09:35 as a reply to  @ post 17279064 |  #31

It depends on what kind of Servo AF focus problems you have. So it's a bit too general a remark to be useful.


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Nov 18, 2014 10:15 |  #32

apersson850 wrote in post #17278884 (external link)
You've misunderstood how AI Servo AF works.

First, One Shot AF is nromally better at acquiring focus than Servo AF. That's due to the time the camera spends doing each of the measurements with the AF sensor.
The 1DX camera is the first one to deviate from this, since it actually uses One Shot AF algorithms for part of the Servo AF service. These parts are those that aren't critical to maintaining the frame rate, like when tracking a subject with AF active but before the trigger button is pressed to start shooting. Thus everyone who claims Servo AF with the ability to turn it off with the AF-ON button is identical to using One Shot AF don't know what they are talking about. It may be good enough for your intended use, but identical, no.

When using Servo AF and taking the first image in a sequence, the camera will behave differently depending on the focus priority setting.
Release: The camera will make one single AF measurement and then drive the lens to whatever position it found from that measurement. If the measurement was correct everything is good. If it was not, the image will not be in focus.
Equal: If the single AF measurement fails, the camera will make a few more attempts (Canon doesn't tell exactly how many - it probably depends on the situation) before the shutter is released. As soon as one of these measurements gave a good result, the lens is focused and the shutter is released. If after some repeated attempts there still is no valid result, it will fire anyway and the image is out of focus.
Focus: The camera will make repeated attempts to measure focus, until it's successful. If never, then it won't fire either.

Now this same procedure continues when taking successive images. Rename release to speed, and you can follow the same explanation. What comes in as extra sugar on the cake here is when you enable more than one AF point. If you do, then the whole battery of algorithms used to try to figure out if the subject escaped from the main AF point and, if so, where it went, comes into play between each image. All the settings used to optimize this behavior are worthy a theseis by themselves, and that's why Canon wrote the AF setup guides.

I fixed the headline the way it should look on the first post, should this end up being a sticky.

Thanks, Anders. Concise and clear.


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Nov 18, 2014 10:46 |  #33

apersson850 wrote in post #17278884 (external link)
You've misunderstood how AI Servo AF works.

First, One Shot AF is nromally better at acquiring focus than Servo AF. That's due to the time the camera spends doing each of the measurements with the AF sensor.
The 1DX camera is the first one to deviate from this, since it actually uses One Shot AF algorithms for part of the Servo AF service. These parts are those that aren't critical to maintaining the frame rate, like when tracking a subject with AF active but before the trigger button is pressed to start shooting. Thus everyone who claims Servo AF with the ability to turn it off with the AF-ON button is identical to using One Shot AF don't know what they are talking about. It may be good enough for your intended use, but identical, no.

When using Servo AF and taking the first image in a sequence, the camera will behave differently depending on the focus priority setting.
Release: The camera will make one single AF measurement and then drive the lens to whatever position it found from that measurement. If the measurement was correct everything is good. If it was not, the image will not be in focus.
Equal: If the single AF measurement fails, the camera will make a few more attempts (Canon doesn't tell exactly how many - it probably depends on the situation) before the shutter is released. As soon as one of these measurements gave a good result, the lens is focused and the shutter is released. If after some repeated attempts there still is no valid result, it will fire anyway and the image is out of focus.
Focus: The camera will make repeated attempts to measure focus, until it's successful. If never, then it won't fire either.

Now this same procedure continues when taking successive images. Rename release to speed, and you can follow the same explanation. What comes in as extra sugar on the cake here is when you enable more than one AF point. If you do, then the whole battery of algorithms used to try to figure out if the subject escaped from the main AF point and, if so, where it went, comes into play between each image. All the settings used to optimize this behavior are worthy a theseis by themselves, and that's why Canon wrote the AF setup guides.

I fixed the headline the way it should look on the first post, should this end up being a sticky.

Hmmm. I just said that if you wanted to gaurantee focus, using Focus was probably the most logical in 1st priority. Your breakdown basically expands the manuals explanation which makes sense. I assumed that was a given so I did not go into an explanation.

As for 2nd priority like you said works basically the same expect they renamed it speed. Just because you set the camera at 10fps does not guarantee 10pfs. Many factors can slow that frame rate down. That is stated in several places in the manual.

I figure one is continually acquiring AF. So if you choose Speed instead of Equal or Focus then the camera does not spend time re-checking or re-focusing on the subject, it just shoots. If you locked on correctly when it took the first shot (1st priority) then your subsequent shots should be locked on. This were I used the term "the camera using less resources".

I'm not sure why else they would offer Speed in 2nd priority. If it did not lock on during the first shot then what is the point of having it? Unless it works with conjunction with 1st priority and release. You get an OOF shot to start with and it just continues to give you OFF shots.


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Nov 18, 2014 10:58 |  #34

Just to add. I want my 5D2 to set to Focus for both. I want the first shot to be in focus and I want the camera to be re-checking focus on subsequent shots when the bride walks down the isle. For birding as long as the focus locks on I want fps to me maximized.


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Nov 18, 2014 12:05 |  #35

I was thinking more about this Anders. I'm basing this on cameras that do not have 1st and 2nd priority options. AI Servo locks, continues to track and you fire away.

With these options I'm assuming that AI Servo locks and tracks. In 2nd priority AI Servo continues to track, but you have the option to tell it to continue to re-confirm focus or not bother, just continue to track after the focus first locks in 1st priority. I'm assuming that AI Servo still continues it's predictive focus function in any of the 3 settings, Equal, Focus or Speed. The addition of the priority feature makes it more sophisticated.

Since this is a learning forum and thread I'm open to a different explanation of this. There is not a lot of info from Canon in this and I will test it. Moving cars will be a good test situation.


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Nov 18, 2014 12:19 as a reply to  @ digital paradise's post |  #36

Well, it could be that I misunderstand your wording. I'm not a native English speaker, you know.

Anyway, when you write that in Speed mode it will just lock and continue, not re-evaluate focus, I'd say that's wrong. Or you don't mean what I mean when I say that.

Since even in Release/Speed mode, the camera will attempt to measure the distance to the subject and focus the lens each and every time before taking a picture. Even in between images taken at 10 frames/s. Thus that's the same for all modes.

The difference is that in Release/Speed mode, it will spend one and one single distance measurement cycle only, when finding the distance to the target. If that measurment fails (i.e. no contrast can be found, since the AF point dropped of that bird and is now covering blue sky), the camera doesn't care, but just continue to shoot and give it a new try before next image. But as long as there's a contrast to measure, each and every shot will be measured, focus re-adjusted and the image will be in focus just as well as it would be in any other AF piority mode.
When in the equal priority mode, it will make a few attempts before giving up and take the photo. In Focus mode, it will defer picture taking until somthing to focus on shows up. Hence frame rate is hardly affected at all by AF in speed mode, but can be somewhat in equal mode and a lot in focus priority mode.

As I said, I may be misunderstanding you, but this isn't exactly what I read into your post.


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Nov 18, 2014 13:29 |  #37

No problem. We have had good conversations before. So 1st priority is pretty basic.

2nd priority. Nope you read it correctly. I was assuming that with Speed it was not re-checking focus. AI Servo continues to track on the locked focus from the first shot and adjusts as the object moves to keep that initial focus locked. To me focus lock and predictive focus are two different things.

I'm perfectly fine that in Speed that it does re-check focus to some degree because I don't know enough about how the system works. Less often that Equal as you explained which makes perfect sense.

According to the manual 2nd priority when set to Focus will not let you fire if it has not re-checked and confirmed focus even after it let you take the first shot (which is controlled by 1st priority).

So I think we were on the same page and just a few details needed to be corrected. Thanks for the info Anders.


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Nov 18, 2014 14:11 |  #38

digital paradise wrote in post #17279749 (external link)
To me focus lock and predictive focus are two different things.

To me, focus lock is a focus setting that's not changing. Like when you use One Shot AF. You can then aim the camera as you like, but if it locked at three meters it stays at three meters.

Focus tracking is when the camera continuously updates the focus distance as new measurements of the distance to the subject brings in new data.

Predictive tracking is when the camera during a sequence of distance measurements have found the subject to be approacing at a certain rate, and the camera then predicts how much the subject will move until the shutter opens after you pressed the trigger button.

AF point handover is the sideways dimension of tracking, where the camera tries to maintain knowledge about which AF point is covering the subject right now.

There's of course some prediction built into tracking as well, since if the camera gets a series of measurements, all furhter away, and then suddenly gets one much closer, it will not fully believe that until more measurements give the same result.


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Nov 18, 2014 14:29 |  #39

apersson850 wrote in post #17279824 (external link)
Focus tracking is when the camera continuously updates the focus distance as new measurements of the distance to the subject brings in new data.

Predictive tracking is when the camera during a sequence of distance measurements have found the subject to be approacing at a certain rate, and the camera then predicts how much the subject will move until the shutter opens after you pressed the trigger button.

I meant this so I'll reword focus lock to focus tracking. It does initially have to lock on before it tracks. Just how I worded it.


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Nov 19, 2014 05:22 as a reply to  @ digital paradise's post |  #40

I see. Then it's like I somewhat suspected, we just used different phrases for the same thing. :) Sometimes not easy to convey the intended meaning even in your native language.


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Nov 19, 2014 06:46 |  #41

Great information...
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Nov 19, 2014 08:07 |  #42

apersson850 wrote in post #17280919 (external link)
I see. Then it's like I somewhat suspected, we just used different phrases for the same thing. :) Sometimes not easy to convey the intended meaning even in your native language.

Yeah, English is not you first language and I tend to write faster than I think. Not a good combination :D


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Nov 19, 2014 09:36 as a reply to  @ digital paradise's post |  #43

Must say, that the basic instruction manual that comes with this camera is a total POS.

had to consult my 5D3 owners manual for a couple of things. That pissed me off.

Here is a link from canon. They went green so no more little green instruction manuals for your bags. You will need to download and put them in your phones if you want it with you.

Lame move canon. I would have paid $1905.00 for the manual to be in the box:rolleyes:

heres the link
http://www.usa.canon.c​om …rk_ii#Brochures​AndManuals (external link)


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Nov 19, 2014 14:12 |  #44

Agreed. Anders had access to some great info on the priority subject compared to the manual. Canon leaves you with trying to interpret how something works but I guess the manual would be so big it would have to come in it's own box. Trying to find the info can be frustrating.

Even the AF PDF does not go into that detail. It states that if speed is selected in second priority "continuous shooting speed will not drop off" which threw me off with the focus re-checking stuff.

http://www.brochures.c​anon-europe.com …ctid=9090&langu​ageid=-111 (external link)

This is a very good thread Mike.


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Nov 19, 2014 20:26 |  #45

The customization options for this camera are awesome. Including the trigger, you can now activate one of 3 distinct shooting modes just by pressing a single button (trigger, AF-ON, *)

So sweet!

PP


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7D2, 1Dx, 5D3 Owners- How to make AF system work better for you
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