# 6D AF and Focal Plane issues by recomposing



## Frage (Jan 13, 2013)

Hello,

I would like to know your thoughts on this topic.
How difficult could be to work with a 6D and a fast lens if you have to recompose (focal plane distance changes) and want to achieve a *shallow DOF* ?


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## robbymack (Jan 13, 2013)

No more difficult than any other camera using the same technique.


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## neuroanatomist (Jan 13, 2013)

http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm

http://digital-photography-school.com/the-problem-with-the-focus-recompose-method


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## Frage (Jan 13, 2013)

neuroanatomist said:


> http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm
> 
> http://digital-photography-school.com/the-problem-with-the-focus-recompose-method



Great links, thanks!

Since recomposig sucks (visual-vacations.com dixit), I was just wondering how it all happens on a 6D.


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## nightbreath (Jan 13, 2013)

There are 3 options I know to avoid focus error while recomposing:
1. Focusing on a subject that is located at the same distance as your subject.
2. Moving yourself forward / backward after recomposing to compensate focus shift.
3. Using AF microadjustment (this one is tricky).


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## Frage (Jan 13, 2013)

robbymack said:


> No more difficult than any other camera using the same technique.


I am not sure about it. Maybe with some cameras you can lock the focus and let the AF system track this spot for you while you recompose. But as I said, I am not sure about it.


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## neuroanatomist (Jan 13, 2013)

Frage said:


> I am not sure about it. Maybe with some cameras you can lock the focus and let the AF system track this spot for you while you recompose. But as I said, I am not sure about it.



Yes, I suppose you could use AI Servi to 'track' to an outer AF point. But that's not focus-recompose, and if you're going to do that, why not just select the outer AF point directly?


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## Frage (Jan 13, 2013)

neuroanatomist said:


> Frage said:
> 
> 
> > I am not sure about it. Maybe with some cameras you can lock the focus and let the AF system track this spot for you while you recompose. But as I said, I am not sure about it.
> ...



Sorry, my english ist quite poor. Maybe I don´t want to say "focus-recompose" but just recomposition. Sometimes you want to recompose to lock the focus and the measured light. 
Well, sometimes you just have not the time to do that in single steps. You just may not get the shot.


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## neuroanatomist (Jan 13, 2013)

You can lock exposure separately from focus. The bottom line is that if you lock focus then move the camera when shooting with a very thin DoF, you'll get backfocus.


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## Frage (Jan 13, 2013)

I see... I just foud out what you can not do with the 6D. I was just interested in this cam, but I think not anymore.


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## robbymack (Jan 13, 2013)

Frage said:


> I see... I just foud out what you can not do with the 6D. I was just interested in this cam, but I think not anymore.



I wouldn't call it a deal breaker just something you have to be mindful of. It also something that can't be overcome with good technique or simply realizing the limitations of what you and cant do. Is it fool proof? No, but then again nothing really is.


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## Frage (Jan 13, 2013)

robbymack said:


> Frage said:
> 
> 
> > I see... I just foud out what you can not do with the 6D. I was just interested in this cam, but I think not anymore.
> ...



Well by the nowdays tech a decent 3d tracking is something that I personally would expect in a ~2000 € body.


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## neuroanatomist (Jan 13, 2013)

The 6D has AI Servo tracking - but when you use the word 'recompose' that implies you're not using it.


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## nightbreath (Jan 13, 2013)

There's also Live View focusing that might work for you


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## robbymack (Jan 13, 2013)

Frage said:


> robbymack said:
> 
> 
> > Frage said:
> ...



I don't think we are talking about the same thing. Focus and recompose to me (and to pretty much everyone) means you lock focus on the subject then recompose the frame (by moving the camera) then click the shutter. This does shift the focal plane and if you are using a razor thin dof you'll end up with some back focus most likely. 3d tracking? I have no idea what you are talking about unless you are simply talking about servo mode in which case I don't think you'll be using focus/recompose. What exactly do you want the camera to be able to do for you?


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## Frage (Jan 13, 2013)

robbymack said:


> Frage said:
> 
> 
> > robbymack said:
> ...



Something like that, actually.
Nikon 3D Auto-focus Tracking]
[url=http://www.youtube.com/watch?v=7EfA1mesLhA#ws]Nikon 3D Auto-focus Tracking[/url]


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## Frage (Jan 13, 2013)

nightbreath said:


> There's also Live View focusing that might work for you



Live View focusing and Canon in the same life?


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## nightbreath (Jan 13, 2013)

Frage said:


> nightbreath said:
> 
> 
> > There's also Live View focusing that might work for you
> ...


Why not? Live View makes the whole image sensor a big autofocus area. If you have time to recompose, you might use Live View instead of recomposing.

I've used that a few times for group shots using 7D with 50mm @ f/1.4 when the whole group made one straight line. This approach gave me high-precision focus with nice blurred-out leaves in 2 meters after the subjects.


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## neuroanatomist (Jan 13, 2013)

Nikon's 3D tracking = Canon's AI Servo.


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## Frage (Jan 13, 2013)

neuroanatomist said:


> Nikon's 3D tracking = Canon's AI Servo.



Oh, thanks. Thats exactly what I wanted to know. Now, does it work properly on the 6D?
I am just afraid, only the 5D MIII (not to mention the 1´s) can perform well in this discipline and €2800 are out of my reach.


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## neuroanatomist (Jan 13, 2013)

Frage said:


> neuroanatomist said:
> 
> 
> > Nikon's 3D tracking = Canon's AI Servo.
> ...



Probably ok on the 6D, but definitely better on the 5DIII.


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## dr croubie (Jan 13, 2013)

+1 for the Tripod, Live-view, 5x or 10x mag, and getting it right the first time.
Set up the tripod, frame, lock the head.
Live-view, magnify in, set your focus.
*ZOOM OUT TO 1x MAG* before you set your light readings (at least on my 7D if you take a light reading at 5x or 10x mag, it might not be accurate for the whole frame).

Not only does focus/recompose not work at f/1.2, or anywhere that DOF is less than a few cm (even 300mm f/4 is wafer thin on FF), but even regular focus is enough of a nightmare in one-shot mode.
I've had scenarios, even with something not-completely-wafer-thin like an EF 85mm f/1.8, in one-shot AF mode where the subject moved 1cm, or I swayed in the wind, or whatever, and it ended up OOF.

The only way I ever shoot under f/2.8 (unless it's on a UWA lens) is with AI Servo, or tripod, liveview, and 5x mag.


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## beansauce (Jan 14, 2013)

If my depth of field is that tight and the possibility of focus shift is evident when using this method, I'll quickly turn on live view, zoom in a bit, and achieve focus MANUALLY. Practice a bit, and this gets fast.


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## J.R. (Jan 14, 2013)

dr croubie said:


> +1 for the Tripod, Live-view, 5x or 10x mag, and getting it right the first time.
> Set up the tripod, frame, lock the head.
> Live-view, magnify in, set your focus.
> *ZOOM OUT TO 1x MAG* before you set your light readings (at least on my 7D if you take a light reading at 5x or 10x mag, it might not be accurate for the whole frame).
> ...



+100 ... pretty much nailed it there


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## Frage (Jan 15, 2013)

beansauce said:


> If my depth of field is that tight and the possibility of focus shift is evident when using this method, I'll quickly turn on live view, zoom in a bit, and achieve focus MANUALLY. Practice a bit, and this gets fast.



I was thinking of using MagicLantern´s Focus Peak, but not in FF camera (I would buy). In a FF camera I want to use the VF.


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## Ryan708 (Jan 15, 2013)

I wonder if some of the lenses that have strong "field curvature" would cancel out the focus-recompose teqnique. if your focal plane was shaped like a " ( " for example, tilting the camera would all be on same focal plane. Sorry If i lost you, im sure a few people will see my point.


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## dr croubie (Jan 15, 2013)

Ryan708 said:


> I wonder if some of the lenses that have strong "field curvature" would cancel out the focus-recompose teqnique. if your focal plane was shaped like a " ( " for example, tilting the camera would all be on same focal plane. Sorry If i lost you, im sure a few people will see my point.



Possibly, but with a caveat.
The reason Focus+recompose doesn't work for a flat plane is because the distances change *if you rotate the camera around the nodal point of the lens*.
If, however, you rotate around your neck (which is what I would probably do), it is still possible (although *highly* unlikely), that you manage to still catch the focus where you want.

With a curved plane of focus (like on a fisheye, which afaik is a curved plane of focus bending around the lens), yes, there is the possibility to rotate around the nodal point and/or around your neck and keep the focus on the intended subject *if you know exactly how the plane is curved and can adjust yourself properly*.
Again, you've probably got just as much chance of catching the focus as with a flat plane.

But, there's one more problem. Lenses with curved planes of focus can also bend the other way, and as far as I know that's a lot more common. ie, focal point is 5m away in the centre of the image, and focus is at infinity on the edges. See the nice graphic here. Focus on something in the centre, turn your head a bit, and suddenly they're even more oof than if you'd used a true flat-planar lens.

So yes, it is technically possible to focus/recompose with all of a flat plane, curved plane towards you, and a curved plane away from you. But unless you know the *exact* distances and *exact* way and shape that the plane of focus is curved, then any photos in focus using this technique will be purely coincidental (and a lucky chance).


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## ishdakuteb (Jan 15, 2013)

Frage said:


> neuroanatomist said:
> 
> 
> > http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm
> ...



well... i certainly can perform either way (re-compose or select one of those focus point) if you can lend me a 6d. i bet that canon 6d is much much better than a camera that i am using everyday for experiment purpose which is canon 30d (note: i am using select focus point on this one).

for ai servo, if i still remember correctly, canon suggests to track your subject starting from center focus point for better result.

one of a renown photographer who prefers to use re-compose technique is bambi cantrell. it is just the matter of technique that you have to train yourself when preferring to use it that way.


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