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Thread started 04 Jan 2015 (Sunday) 12:51
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Back Buttton focusing (BBF) and Image Stabilization (IS)

 
WesternGuy
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Jan 04, 2015 12:51 |  #1

In a recent discussion with a fellow photographer about BBF, he asked me if I knew how BBF affected IS, if at all. I wasn't sure, so I thought I would post the question here. Does BBF have any affect on how IS works?. Basically, there are two ways to focus a lens on a DSLR and that is through shutter button focusing or BBF. The question becomes whether or not the lens knows how it was focused, as my understanding is that IS kicks in once the lens has obtained focus. IS then attempts to keep the subject in focus by correcting for any minor movements of the lens. He was concerned that changing the focus of his camera and lens from shutter button focus to BBF would change the way that IS worked. My contention is that this would not change the way IS worked because the lens doesn't know how it was focused, only that it was focused and once it is focused then IS attempts to maintain that focus. So I am looking for an answer to that question from someone who is more knowledgeable on the subject than I am. Any insight that anyone would care to contribute will be greatly appreciated. Thanks.

WesternGuy




  
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GeoKras1989
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Jan 04, 2015 14:20 |  #2
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I am not sure if it is a setting, or I am just really lucky. I shoot 6D/60D with BBAF and all my IS/OS lenses kick in when I hit the BB for AF.


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buddy4344
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Jan 04, 2015 14:41 |  #3

This is a great question. I know some using AI servo and BBF a subject then recompose before the click. In this case it would seem the shooter is not getting IS at the time of exposure


Buddy4344

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johnf3f
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Jan 04, 2015 14:44 |  #4

It makes no difference on my 1DX and a friend's 1D4. If you press either the shutter release or AF On button the IS fires up as normal.
Just a suggestion, I only use IS when really needed - which isn't that often. As a result I am getting faster, more accurate AF and better tracking. I turned the IS off on my (4) lenses that have it and have noticed an improved "Hit" rate. Naturally you still have the IS in reserve for poor lighting conditions when it can come in really handy!


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john ­ crossley
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Jan 04, 2015 14:45 |  #5

WesternGuy wrote in post #17365677 (external link)
In a recent discussion with a fellow photographer about BBF, he asked me if I knew how BBF affected IS, if at all. I wasn't sure, so I thought I would post the question here. Does BBF have any affect on how IS works?. Basically, there are two ways to focus a lens on a DSLR and that is through shutter button focusing or BBF. The question becomes whether or not the lens knows how it was focused, as my understanding is that IS kicks in once the lens has obtained focus. IS then attempts to keep the subject in focus by correcting for any minor movements of the lens. He was concerned that changing the focus of his camera and lens from shutter button focus to BBF would change the way that IS worked. My contention is that this would not change the way IS worked because the lens doesn't know how it was focused, only that it was focused and once it is focused then IS attempts to maintain that focus. So I am looking for an answer to that question from someone who is more knowledgeable on the subject than I am. Any insight that anyone would care to contribute will be greatly appreciated. Thanks.

WesternGuy

Image Stabilisation doesn't keep the subject in focus. Image Stabilisation stabilises the image.


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Philihase
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Jan 04, 2015 14:48 |  #6

At least with the 70D If you focus using bbf the IS will spool up. If you half press the shutter button it will also spool up independant of the back button. So long as you bbf , recompose and half press the shutton button it will keep spooled up. Plus I think the Sigma IS stays spooled up till the display clears in the viewfinder.


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archer1960
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Jan 04, 2015 15:07 as a reply to  @ Philihase's post |  #7

As others have said, the IS kicks in when you press either the BBF, or half-press the shutter. The IS really helps you keep the focus point on the subject, enabling better shots.


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buddy4344
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Jan 04, 2015 16:02 as a reply to  @ archer1960's post |  #8

great explanations. that makes a lot of sense to me.


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SkipD
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Jan 04, 2015 16:42 |  #9

john crossley wrote in post #17365908 (external link)
Image Stabilisation doesn't keep the subject in focus. Image Stabilisation stabilises the image.

The above is correct. Canon's Image Stabilization (IS) does absolutely nothing to focus the lens. All it does is counteract the up-down and left-right (or combinations, of course) motion of the lens. The result is that the image being projected into the camera moves less than if IS were not active.


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mwsilver
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Post edited over 4 years ago by mwsilver.
     
Jan 05, 2015 00:17 |  #10

WesternGuy wrote in post #17365677 (external link)
In a recent discussion with a fellow photographer about BBF, he asked me if I knew how BBF affected IS, if at all. I wasn't sure, so I thought I would post the question here. Does BBF have any affect on how IS works?. Basically, there are two ways to focus a lens on a DSLR and that is through shutter button focusing or BBF. The question becomes whether or not the lens knows how it was focused, as my understanding is that IS kicks in once the lens has obtained focus. IS then attempts to keep the subject in focus by correcting for any minor movements of the lens. He was concerned that changing the focus of his camera and lens from shutter button focus to BBF would change the way that IS worked. My contention is that this would not change the way IS worked because the lens doesn't know how it was focused, only that it was focused and once it is focused then IS attempts to maintain that focus. So I am looking for an answer to that question from someone who is more knowledgeable on the subject than I am. Any insight that anyone would care to contribute will be greatly appreciated. Thanks.

WesternGuy

Using BBF has absolutely no impact on IS. IS will activate and work identically to when focus is achieved using the shutter button. IS does not keep anything in focus. Its only job to is stabilize the image at generally slower shutter speeds in order to counter blurring resulting from handheld camera shake. IS is solely intended for static subjects and has no useful purpose if the subject is moving.


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WesternGuy
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Jan 05, 2015 01:43 |  #11

john crossley wrote in post #17365908 (external link)
Image Stabilisation doesn't keep the subject in focus. Image Stabilisation stabilises the image.

Good point, but does not stabilizing the image also keep it in focus? My understanding is that IS corrects for minute shaking of the camera from handholding. I would think that if the image would ordinarily blur from hand shake, then it is not going to be in focus. I know it won't protect from blur caused by the subject itself moving, but that is a bit different than blur introduced by an unsteady hand. To me if the camera is "shaken" when the picture is being taken, then the subject will not be in focus because I always think of an "in-focus" image as being sharp whereas a blurry image is not sharp and thus not in focus. Maybe we are arguing semantics here, but I have always gone on the assumption that a blurred image is out of focus regardless of how it got "out of focus".

WesternGuy




  
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SkipD
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Post edited over 4 years ago by SkipD.
     
Jan 05, 2015 03:32 |  #12

WesternGuy wrote in post #17366806 (external link)
Good point, but does not stabilizing the image also keep it in focus? My understanding is that IS corrects for minute shaking of the camera from handholding. I would think that if the image would ordinarily blur from hand shake, then it is not going to be in focus. I know it won't protect from blur caused by the subject itself moving, but that is a bit different than blur introduced by an unsteady hand. To me if the camera is "shaken" when the picture is being taken, then the subject will not be in focus because I always think of an "in-focus" image as being sharp whereas a blurry image is not sharp and thus not in focus. Maybe we are arguing semantics here, but I have always gone on the assumption that a blurred image is out of focus regardless of how it got "out of focus".

I suppose that, at times, motion blur in an image is mistaken for something being out of focus. However, the two are very different.

A camera's lens can be very sharply focused and, if the camera is not held stable, the entire image can be blurred due to camera/lens motion. The blur due to motion is VERY different than an out-of-focus situation.

  • Camera motion blur will affect the entire image because the image is being dragged across the film or sensor while the shutter is open.
  • A focus error will only affect elements of the image that are at a specific distance range from the camera. In other words, you may have inadvertently focused in front of or behind a portrait subject's face making the face blurry while other elements of the image are quite sharp.

Skip Douglas
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jc1350
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Jan 05, 2015 09:23 |  #13

WesternGuy wrote in post #17366806 (external link)
Good point, but does not stabilizing the image also keep it in focus? My understanding is that IS corrects for minute shaking of the camera from handholding. I would think that if the image would ordinarily blur from hand shake, then it is not going to be in focus. I know it won't protect from blur caused by the subject itself moving, but that is a bit different than blur introduced by an unsteady hand. To me if the camera is "shaken" when the picture is being taken, then the subject will not be in focus because I always think of an "in-focus" image as being sharp whereas a blurry image is not sharp and thus not in focus. Maybe we are arguing semantics here, but I have always gone on the assumption that a blurred image is out of focus regardless of how it got "out of focus".

WesternGuy

Here is a video with examples that explains the difference between blurry and out-of-focus images.

http://www.adorama.com …n-blurry-and-out-of-focus (external link)


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SkipD
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Jan 05, 2015 10:12 |  #14

jc1350 wrote in post #17367124 (external link)
Here is a video with examples that explains the difference between blurry and out-of-focus images.

http://www.adorama.com …n-blurry-and-out-of-focus (external link)

A problem I have with the video is that it tries to make the word "blurry" apply only to motion-related blur. Something that is out of focus is also blurry but for a different reason than motion-related blur. The terminology can be confusing to a newbie, but I hope that WesternGuy is getting the right information.


Skip Douglas
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WesternGuy
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Jan 06, 2015 19:55 |  #15

SkipD wrote in post #17367215 (external link)
A problem I have with the video is that it tries to make the word "blurry" apply only to motion-related blur. Something that is out of focus is also blurry but for a different reason than motion-related blur. The terminology can be confusing to a newbie, but I hope that WesternGuy is getting the right information.

Skip, no problem. I am pretty sure I can tell the difference. Thanks.

WesternGuy




  
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Back Buttton focusing (BBF) and Image Stabilization (IS)
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