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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 10 Sep 2013 (Tuesday) 07:19
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back button auto focus...

 
Dave ­ Jenkins
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Sep 30, 2013 16:04 |  #91

apersson850 wrote in post #16336318 (external link)
It was more relevant back then, when the number of options in the menu was far less than it is today.

True, and I liked it that way. But I've been deep-diving in the OM-D menu for the past year, and even the 6D is simple in comparison to that.


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BigAl007
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Oct 02, 2013 02:06 |  #92

subway surfer wrote in post #16336392 (external link)
are you saying you achieve one shot focusing by just tapping BBF? I Thought when in Al Servo the camera looks for movement is this true or you do not notice any difference and still achieve good focus. i still switch.

Personally I leave my camera in AI Servo/BBF and as Teamspeed have the best of both worlds. I don't really need a beep/light to tell me the camera is in focus. So press the back button when focus is good let go. That deals with recompose when needed, or shooting a fixed object from a tripod. Otherwise you just hold the button and the system keeps tracking your/subject movement. If you have to say pan through something big enough to drag the focus off target then release the back button. I'm shooting an older body (20D) and it has less options, annoyingly as you have to reasign the * button and no deicated bbaf button you have to wake the camera with a half press of the shutter button.

Alan


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apersson850
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Oct 02, 2013 04:53 as a reply to  @ BigAl007's post |  #93

It has been said a number of times, but we can do it again:

  • Precision is inferior when using Servo AF, since it's optimized for as quick use of the AF sensors as possible. This decreases the signal/noise ratio on the AF sensor chip.
  • Low light sensitivity is inferior when using Servo AF, for the very same reason.
  • To add to that, there's no AF assist from your flash in Servo AF.
Apart from that, you can simulate One shot AF by releasing the AF-ON button when appropriate, when you use Servo AF.

Anders

  
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GregDunn
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Oct 02, 2013 10:17 |  #94

apersson850 wrote in post #16340237 (external link)
Precision is inferior when using Servo AF, since it's optimized for as quick use of the AF sensors as possible. This increases the signal/noise ratio on the AF sensor chip.

I'm puzzled - or is this a typo? One would think that sampling the AF system faster would decrease the S/N ratio because of shorter integration times.


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apersson850
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Oct 02, 2013 11:59 as a reply to  @ GregDunn's post |  #95

When you underexpose an image, do you get more or less noise, when you lift it in post?

Ah, now I see the mistake. Sorry. Corrected.


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GregDunn
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Oct 02, 2013 12:11 |  #96

Makes sense now. :) Thanks!


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bugler
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Oct 02, 2013 13:12 |  #97

I tried back button last night in studio with my new 6D. Not sure I'll be able to get the hang of it. Any advice?


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Oct 02, 2013 13:49 |  #98

sancho1983 wrote in post #16285579 (external link)
I don't really get the benefits?

It seems like it's an extra button to press when I have to press the shutter button anyway? (which would normally trigger the focus lock)

I tend to agree with this. However, I know there must be advantages or all of these good photographers wouldn't be raving about it, so I think it deserves a further look-see.


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foxbodychris
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Oct 02, 2013 21:39 |  #99

bugler wrote in post #16341107 (external link)
I tried back button last night in studio with my new 6D. Not sure I'll be able to get the hang of it. Any advice?

It takes some time but after a day of shooting I am so used to I dont even think about it anymore. Give it some time you will love it


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apersson850
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Oct 03, 2013 03:06 |  #100

guntoter wrote in post #16341180 (external link)
I tend to agree with this. However, I know there must be advantages or all of these good photographers wouldn't be raving about it, so I think it deserves a further look-see.

For the typical One Shot AF photos of non-moving targets, taken at your own ease, there's hardly any advantage at all.

Imagine standing near the finishing line for a sports event, being bumped around by 50 other spectators/photographe​rs, holding your camera with something like the EF 70-200 mm f/2.8L IS II USM mounted. Your task is now to start Servo AF tracking as soon as the competitor you want to take photos of shows up at line-of-sight, then keep tracking while taking an occasional photo now and then. At the same time, you may want to skip tracking occasionally, when other people or objects block the line-of-sight, but an image take could still make sense, since the obstruction will be out of focus. Provided you don't keep on tracking then, of course. Once the obstruction has cleared the path, you want to resume tracking again.
When the competitor comes up close, you want to fire off a number of photos, using high speed continuous drive, at the same time as you want to use a different AF point, higher up in the viewfinder. You may also want to change to a larger coverage of AF points during that moment.

By programming AF-ON to focus with the selected point, * to focus with the registered point and M-Fn2 (or depth-of-field preview) to switch to a different AF setup, you can accomplish all this without having to resort to having to hold a certain button at some intermediate position. It's either on or off in this case. Besides, letting go of tracking and still take photos isn't just difficult the normal way, it's impossible.


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guntoter
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Oct 03, 2013 10:26 |  #101

apersson850 wrote in post #16342639 (external link)
For the typical One Shot AF photos of non-moving targets, taken at your own ease, there's hardly any advantage at all.

Imagine standing near the finishing line for a sports event, being bumped around by 50 other spectators/photographe​rs, holding your camera with something like the EF 70-200 mm f/2.8L IS II USM mounted. Your task is now to start Servo AF tracking as soon as the competitor you want to take photos of shows up at line-of-sight, then keep tracking while taking an occasional photo now and then. At the same time, you may want to skip tracking occasionally, when other people or objects block the line-of-sight, but an image take could still make sense, since the obstruction will be out of focus. Provided you don't keep on tracking then, of course. Once the obstruction has cleared the path, you want to resume tracking again.
When the competitor comes up close, you want to fire off a number of photos, using high speed continuous drive, at the same time as you want to use a different AF point, higher up in the viewfinder. You may also want to change to a larger coverage of AF points during that moment.

By programming AF-ON to focus with the selected point, * to focus with the registered point and M-Fn2 (or depth-of-field preview) to switch to a different AF setup, you can accomplish all this without having to resort to having to hold a certain button at some intermediate position. It's either on or off in this case. Besides, letting go of tracking and still take photos isn't just difficult the normal way, it's impossible.

Thanks for this input. As you mentioned, I hardly ever find myself in those situations. I do occasionally take action in sports, so I will give that technique a try under those situations.


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qdrummer21
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Oct 03, 2013 15:39 |  #102

The biggest, non-subjective, benefit I've found with back button AF has been shooting action outdoors with servo for extended period of times (4+ hours) in temperatures dropping below 0F after windchill. Trying to hold the shutter button down exactly halfway with the total loss of tactile sensation due to wearing thick winter gloves is nearly impossible, way too many accidental shutter actuations or the AF disengaging when I didn't want it to. With back button AF I can hold the button knowing that's it's only going to trigger the AF and not worry about it accidently stopping the AF.




  
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bugler
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Oct 03, 2013 18:00 |  #103

So is this less beneficial in a studio situation? I understand the uses for action and such.


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flashpoint99
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Oct 03, 2013 18:09 |  #104

bugler wrote in post #16341107 (external link)
I tried back button last night in studio with my new 6D. Not sure I'll be able to get the hang of it. Any advice?

changed to BBF 20 min before a vintage cart shoot last year, felt 100% natural right from the start....Now its instinctual ..have not and will not go back to half pressing the shutter again.




  
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apersson850
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Oct 04, 2013 01:51 |  #105

bugler wrote in post #16344184 (external link)
So is this less beneficial in a studio situation? I understand the uses for action and such.

Actually not. In a studio situation, I find myself often separate the tast of focusing and metering (and some other tasks too, but they're not relevant here).
By using back button focusing, I can use AF support for focusing when I want to, focus manually when I want to and also start metering (half-press) when I want to, all without any of them affecting any other.

I find that beneficiary.

It's for the everyday foot - aim - fire snaps I find back button focusing least useful. Even if it works there too.


Anders

  
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