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Author Topic: What's the big deal with the AF?  (Read 3916 times)

Mark1

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What's the big deal with the AF?
« on: March 01, 2012, 07:56:38 PM »
I'm on my 3rd EOS digital body now with virtually the same AF - 30D / 5D / 5D2 and I've NEVER had cause to complain about the AF. It works just fine for me for candid portraits, street, landscape and some amateur wildlife stuff.

I use centre point only and recompose. I use this method solely because I want to be 100% sure that the camera focuses on where I want it to focus. I like shallow depth of field stuff and so the focus point has to be perfect.

I'm interested to know what people will do with more than 60 AF points because aside from sports and some wildlife where you switch to servo I can't fathom the reasoning.

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What's the big deal with the AF?
« on: March 01, 2012, 07:56:38 PM »

tt

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Re: What's the big deal with the AF?
« Reply #1 on: March 01, 2012, 08:04:04 PM »
I'm on my 3rd EOS digital body now with virtually the same AF - 30D / 5D / 5D2 and I've NEVER had cause to complain about the AF. It works just fine for me for candid portraits, street, landscape and some amateur wildlife stuff.

I use centre point only and recompose. I use this method solely because I want to be 100% sure that the camera focuses on where I want it to focus. I like shallow depth of field stuff and so the focus point has to be perfect.

I'm interested to know what people will do with more than 60 AF points because aside from sports and some wildlife where you switch to servo I can't fathom the reasoning.
Might depend in part on what your normal f stop, focal length and subject movement is?
As you said you use the centre point and focus and recompose.
I imagine an experiment would be to use another focus point and track a moving subject on AI Servo mode.

Isurus

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Re: What's the big deal with the AF?
« Reply #2 on: March 01, 2012, 08:04:19 PM »
I think you answered your own question.  Basically, improved AF is very important/useful for those of us that photograph sports, wildlife, and other moving objects (my little kids who can't sit still, for example).  Focus and recompose won't work in these situations and manual focus is very difficult with lower hit rates.  Even for weddings I think it is important.  While the movement is slower, it is critical that focus is dead on because the moments of the ceremony go by quickly and aren't repeated.

In short, certain situations can be photographed much easier with better hit rates if the AF system is accurate.

PhotonCanvas

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Re: What's the big deal with the AF?
« Reply #3 on: March 01, 2012, 08:12:18 PM »
I shoot with a 5D, mostly landscapes. I do on occasion shoot fast indoor sports with AI focusing and never had any trouble. Those who clamor for multi-point focus points tend to forget that in an action scene the more focus points they have the more likely the camera will focus on the wrong subject.

randplaty

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Re: What's the big deal with the AF?
« Reply #4 on: March 01, 2012, 08:16:39 PM »
Hmm, well I shoot weddings with a 5DmkII and during receptions the AF is pretty much horrible.  I use center and recompose also.  I have to use a flash in order to get the AF assist even if I don't want to use flash.  There are at least 100 blurry shots I shoot every wedding that could possibly have been saved with better AF.  There is a LOT of hunting. 

wickidwombat

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Re: What's the big deal with the AF?
« Reply #5 on: March 01, 2012, 08:17:15 PM »
I'm on my 3rd EOS digital body now with virtually the same AF - 30D / 5D / 5D2 and I've NEVER had cause to complain about the AF. It works just fine for me for candid portraits, street, landscape and some amateur wildlife stuff.

I use centre point only and recompose. I use this method solely because I want to be 100% sure that the camera focuses on where I want it to focus. I like shallow depth of field stuff and so the focus point has to be perfect.

I'm interested to know what people will do with more than 60 AF points because aside from sports and some wildlife where you switch to servo I can't fathom the reasoning.

I think you kind of answered you own question.

why do you use the center point only? its because the other points are unreliable isnt it hence center point focus and recompose this method works.

however if you have a good AF system with a broader spread of points and good outer points you get to select the point more appropriate for you composition and compose focus and shoot. If the AF system is up to it this method is both faster and more accurate. I you get to use a 1D and try this method you will understand the massive difference in this regard.

as to the 61 points, the more points the more accurate the AI servo will track and hand over from point to point
number of points is all about focus tracking. the 9 point system is really not very good when it comes to focus tracking.

As neuro has also said the fact that the 1D meters where you have selected the AF point is also great (and essential if you are shooting in aperture priority or shutter priority however if you shoot manual and meter first its not really an issue as long as you under stand where in your frame the camera is metering)

Its all about fully understanding how your particular AF system works and where its limitations are. as soon as you try to exceed any limitation its going to cause frustration. If you know the limits and work within them then everything is fine :)
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Isurus

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Re: What's the big deal with the AF?
« Reply #6 on: March 01, 2012, 08:20:13 PM »
I shoot with a 5D, mostly landscapes. I do on occasion shoot fast indoor sports with AI focusing and never had any trouble. Those who clamor for multi-point focus points tend to forget that in an action scene the more focus points they have the more likely the camera will focus on the wrong subject.

Just out of curiosity, have you used a 1D series camera in the same situation?  I agree the 5D can handle it, but I think a 1D does better.  To be honest, I find the view finder blackout period and slow frame rate to be more annoying on the 5D than the AF in these situations and would always reach for a 1D series first. 

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Re: What's the big deal with the AF?
« Reply #6 on: March 01, 2012, 08:20:13 PM »

Isurus

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Re: What's the big deal with the AF?
« Reply #7 on: March 01, 2012, 08:22:50 PM »
I'm on my 3rd EOS digital body now with virtually the same AF - 30D / 5D / 5D2 and I've NEVER had cause to complain about the AF. It works just fine for me for candid portraits, street, landscape and some amateur wildlife stuff.

I use centre point only and recompose. I use this method solely because I want to be 100% sure that the camera focuses on where I want it to focus. I like shallow depth of field stuff and so the focus point has to be perfect.

I'm interested to know what people will do with more than 60 AF points because aside from sports and some wildlife where you switch to servo I can't fathom the reasoning.

I think you kind of answered you own question.

why do you use the center point only? its because the other points are unreliable isnt it hence center point focus and recompose this method works.

however if you have a good AF system with a broader spread of points and good outer points you get to select the point more appropriate for you composition and compose focus and shoot. If the AF system is up to it this method is both faster and more accurate. I you get to use a 1D and try this method you will understand the massive difference in this regard.

as to the 61 points, the more points the more accurate the AI servo will track and hand over from point to point
number of points is all about focus tracking. the 9 point system is really not very good when it comes to focus tracking.

As neuro has also said the fact that the 1D meters where you have selected the AF point is also great (and essential if you are shooting in aperture priority or shutter priority however if you shoot manual and meter first its not really an issue as long as you under stand where in your frame the camera is metering)

Its all about fully understanding how your particular AF system works and where its limitations are. as soon as you try to exceed any limitation its going to cause frustration. If you know the limits and work within them then everything is fine :)

Your last comment is spot on.  You must understand and work within the capabilities of your AF system.  If you are willing to put the time into understanding how certain 1D AF settings work in certain situations you can really get incredible results.

Mark1

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Re: What's the big deal with the AF?
« Reply #8 on: March 01, 2012, 08:31:11 PM »
I bought my 5D2 a couple of weeks ago and have been using it in conjunction with a 50mm F1.4 - a great combination of speed, accuracy and light weight. I dont use the outer points because when taking pictures of moving children there simply isn't the time to alter too many settings. you have to have your camera and lens set up and ready to shoot which is why centre point focusing works perfect for me. It's a one-size-fits-all method of focusing where I still have 100% creative control.

If I start fiddling around with the AF settings the moment is lost! I havent ever used a 1 series body or a 7D for that matter and perhaps the problem is that people expect the multipoint predictive AF to nail perfect shallow DOF portraits for them as well as motor cars speeding towards them at 150mph!




neuroanatomist

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Re: What's the big deal with the AF?
« Reply #9 on: March 01, 2012, 08:56:29 PM »
Focus-recompose with an aperture wider than f/2 and a close subject = back focus.  That's simple geometry - the sensor is flat, and the lens field is flat (or it's supposed to be, at least), but when you focus-recompose, you move the camera in an arc, meaning you've decreased the distance to the subject, meaning the plane of critical focus ends up behind where you want it.  With a deeper Dof, or if you don't print large (or look too closely), the effect is masked.  But with a shallow DoF, it's an issue not having a reliable AF point at least close to where you actually need it.

The 5DII has the worst AF point spread of any current Canon body (relative to the frame) - even the entry-level Rebel/xxxD/xxxxD bodies have an AF point closer to the rule-of-thirds intersections.  The center point of the 5DII is good, but it's usually not where you need it, and the outer points of the 5DII, besides having a rather pathetic distribution, aren't very reliable.

A 61-pt AF in the 5DIII, even if it's a simplified version of what's in the 1D X, will be most welcome!
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SiliconVoid

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Re: What's the big deal with the AF?
« Reply #10 on: March 01, 2012, 08:57:14 PM »
As a 5DmkII user I too never experienced any major issues with the 9-point AF that could not be worked with, nor have I ever encountered a situation where I could say a shot was missed because the mkII did not have a better AF system. Quite the contrary, shooting since the late 70s I am perfectly comfortable manual focusing and even one AF point can be used with great efficiency.

I think the most significant issue with the mkII AF system is that it is far outdated. Heck it was outdated when it was released compared to the first 'pro' EOS-1D which was released almost a decade earlier. So in this case the new 5DmkIII is not only an update to the previous model, but for the first time in the history of the 5D it gains the same AF system as the current recently announced top of the line pro 1D series. I am surprised to hear the AF system is the same between the two, at least the rumored specifications, and we will see for sure in a few hours. If it is indeed the same and not some downgraded variant, which would be the norm, that would again magnify the significance.  :)
« Last Edit: March 01, 2012, 08:59:18 PM by SiliconVoid »
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neuroanatomist

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Re: What's the big deal with the AF?
« Reply #11 on: March 01, 2012, 09:14:34 PM »
Note: same AF sensor does not mean same AF system.  The 5DIII (rumored) specs indicate 63-zone iFCL metering, not the 100,000 pixel RGB metering sensor of the 1D X that feeds tracking data to the AF system and drives the facial recognition/tracking.  Nor will there apparently be a separate Digic processor to handle AF.
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Re: What's the big deal with the AF?
« Reply #12 on: March 01, 2012, 10:31:42 PM »
Note: same AF sensor does not mean same AF system.  The 5DIII (rumored) specs indicate 63-zone iFCL metering, not the 100,000 pixel RGB metering sensor of the 1D X that feeds tracking data to the AF system and drives the facial recognition/tracking.  Nor will there apparently be a separate Digic processor to handle AF.

Looks like I called it... 

- I can see these specs being accurate if the 5DMK3 is released at $3500-$4000.

- They could pull off using the 61 point auto-focus, no reason not to... but the 100,000 pixel RGB metering will be absent, as will all the features that come with it, like the intelligent tracking and spot metering using the active AF points. So the 1D X will still be well ahead of the 5DMK3 when it comes to mission critical action shots, and evaluative metering.

Makes me think I'll be definately be getting the 1DX, especially since the 5D3 won't be available until September... according to the grapevine anyway.
« Last Edit: March 01, 2012, 10:35:21 PM by Wrathwilde »

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Re: What's the big deal with the AF?
« Reply #12 on: March 01, 2012, 10:31:42 PM »

SiliconVoid

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Re: What's the big deal with the AF?
« Reply #13 on: March 01, 2012, 10:54:28 PM »
Yes, I apologize for any confusion I may have caused.
My reference to the same AF system was specifically in regard to the physical AF points, as that was the context of the OP and other posts.
As I am not an engineer in this field I could not say exactly what level of involvement the metering system has with the AF sensor and mechanism. As the exposure metering system plays a greater role in the exposure of the image capture (where Canon or any other manufacturer would put their greatest effort towards their most professional/expensive bodies) there is nothing to say that the part of the metering system that benefits AF does not function as reliably in the 5DmkIII as it does in the 1DX.
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Daniel Flather

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Re: What's the big deal with the AF?
« Reply #14 on: March 01, 2012, 11:15:00 PM »
Focus-recompose with an aperture wider than f/2 and a close subject = back focus.  That's simple geometry - the sensor is flat, and the lens field is flat (or it's supposed to be, at least), but when you focus-recompose, you move the camera in an arc, meaning you've decreased the distance to the subject, meaning the plane of critical focus ends up behind where you want it. 

+1

Try that with the 50L wide open, yikes.  50L is awesome when it all lines up.
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Re: What's the big deal with the AF?
« Reply #14 on: March 01, 2012, 11:15:00 PM »