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Archive 2017 · Will micro adjustment affect both kinds if autofocus?

  
 
tsinsf
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p.1 #1 · p.1 #1 · Will micro adjustment affect both kinds if autofocus?


My 70-200 f4 needs a micro focus adjustment on my 5d IV, at least in Live View where I do the majority of my autofocusing. If I do a micro adjustment using Live View autofocus, will that also affect the througj the view finder auto focus?


Oct 18, 2017 at 02:34 PM
Herb
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p.1 #2 · p.1 #2 · Will micro adjustment affect both kinds if autofocus?


Try it and find out...


Oct 18, 2017 at 03:01 PM
dmcphoto
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p.1 #3 · p.1 #3 · Will micro adjustment affect both kinds if autofocus?


Micro focus adjustment (MFA) was devised to compensate for any difference in focus at the phase detect AF sensor and the image sensor. Differences happen because the PDAF sensor and image sensor are two different things located in two different places. Assuming you do your focusing in live view (i.e.; using the same image sensor that creates the photo) MFA is irrelevant and has no effect. Focusing the image on the image sensor makes a sharp photo, period.


Oct 18, 2017 at 03:24 PM
Mikehit
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p.1 #4 · p.1 #4 · Will micro adjustment affect both kinds if autofocus?


MFA does not affect AF on LiveView focussing. It only affects focussing that is done with the mirror down.


Oct 18, 2017 at 04:44 PM
RobDickinson
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p.1 #5 · p.1 #5 · Will micro adjustment affect both kinds if autofocus?


yep live view shouldnt need MFA as the af is in exactly the same plane as the sensor.

With normal PDAF it isnt, so it has to calculate a little then tell the lens 'go here' which can be a little wrong so you get 'go here +4'

With live view your camera is sending 'go here' and your lens is getting it wrong.



Oct 18, 2017 at 04:54 PM
tsinsf
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p.1 #6 · p.1 #6 · Will micro adjustment affect both kinds if autofocus?


If I manually focus in Live View, then switch to Autofocus, the sharpness degrades a little bit. Just a little, but noticable. The problem is worse with my 70-200 F4 II, much less with my 24-70 f2.8 and 100-400 II. Is it a correct assumption that it is a lens issue, and should I sent the lenses in for inspection? Or is there another solution to try. Thanks so much for you help!!


Oct 18, 2017 at 08:06 PM
RobDickinson
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p.1 #7 · p.1 #7 · Will micro adjustment affect both kinds if autofocus?


possibly thats just the af working, it adjusts to its best closest point, they are not infinitely variable , more modern lenses have more positions.


Oct 18, 2017 at 08:22 PM
Peter Figen
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p.1 #8 · p.1 #8 · Will micro adjustment affect both kinds if autofocus?


"If I manually focus in Live View, then switch to Autofocus, the sharpness degrades a little bit. Just a little, but noticable. The problem is worse with my 70-200 F4 II, much less with my 24-70 f2.8 and 100-400 II. Is it a correct assumption that it is a lens issue, and should I sent the lenses in for inspection? Or is there another solution to try. Thanks so much for you help!!"

If the image is "degrading" compared to manual focus, then it's almost entirely in the AF system and this is just what AFMA is for. You need to determine if the autofocus is putting you in front of or behind where your manual best focus is, and you have to make sure you're using a single AF point and it is indeed placed over the point of desired focus. On top of that, you need to take a bunch of AF sample photos as there is always some variability in autofocus even when the camera is locked down and the subject is stationary. You'll get a feel for what is best pretty quickly. I like doing this tethered to a computer and immediately looking at the images at 100 percent view.



Oct 18, 2017 at 08:46 PM
Zenon Char
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p.1 #9 · p.1 #9 · Will micro adjustment affect both kinds if autofocus?


RobDickinson wrote:
yep live view shouldnt need MFA as the af is in exactly the same plane as the sensor.

With normal PDAF it isnt, so it has to calculate a little then tell the lens 'go here' which can be a little wrong so you get 'go here +4'

With live view your camera is sending 'go here' and your lens is getting it wrong.


If it appears LV needs MFA then the camera should go to Canon for service.



Oct 18, 2017 at 09:00 PM
scalesusa
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p.1 #10 · p.1 #10 · Will micro adjustment affect both kinds if autofocus?


If AF is not near perfect in Liveview, its very possibly a lens issue, the lens may not focusing where the signal from the camera tells it to, or is hanging up internally. Live AF is not perfect, you can always improve it a tiny amount by manually focusing, but its so close to perfect that it should not normally matter.


Oct 18, 2017 at 11:41 PM
RobDickinson
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p.1 #11 · p.1 #11 · Will micro adjustment affect both kinds if autofocus?


Zenon Char wrote:
If it appears LV needs MFA then the camera should go to Canon for service.


More likely the lens but they will probably need both anyhow



Oct 19, 2017 at 01:41 AM
Andrew J
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p.1 #12 · p.1 #12 · Will micro adjustment affect both kinds if autofocus?


Sounds like a lens element is decentered.


Oct 19, 2017 at 02:37 AM
Zenon Char
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p.1 #13 · p.1 #13 · Will micro adjustment affect both kinds if autofocus?


RobDickinson wrote:
More likely the lens but they will probably need both anyhow


Good point.



Oct 19, 2017 at 08:13 AM
snapsy
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p.1 #14 · p.1 #14 · Will micro adjustment affect both kinds if autofocus?


It's a good question and actually more involved than some might think at first blush. Dual-pixel AF in LV uses the same phase-detect idea as viewfinder AF - it compares the phase differential of two alternate entries of light to determine establish whether the subject is in focus and if OOF, which direction focus need to be moved to bring the subject into focus. Because of this, dual-pixel AF (and other on-chip phase detection techniques like what Sony uses) are subject to some of the same vulnerabilities that can negatively affect its accuracy (ie, issues that affect one of those entries of light through the lens and not the other). This would include tilted lens mounted and decentered/tilted elements. However dual-pixel wouldn't be vulnerable to PDAF sensor alignment or submirror alignment issues like viewfinder AF is.

Some speculate that Canon's dual-pixel AF implementation uses a combination of phase detect and contrast detect - phase detect to get focus close, then contrast detect for precise focus movement and verification. If this is true then it negate any of the aforementioned issues that plague viewfinder AF.

It's unclear whether user-configured microadjustment values have any effect on the dual-pixel AF operation.



Oct 19, 2017 at 10:18 AM
scalesusa
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p.1 #15 · p.1 #15 · Will micro adjustment affect both kinds if autofocus?


snapsy wrote:
Some speculate that Canon's dual-pixel AF implementation uses a combination of phase detect and contrast detect - phase detect to get focus close, then contrast detect for precise focus movement and verification. If this is true then it negate any of the aforementioned issues that plague viewfinder AF.

It's unclear whether user-configured microadjustment values have any effect on the dual-pixel AF operation.


I don't think the contrast detect portion is speculation, because the Canon DPAF patent spells it out. As far as I can determine, it is still the way DPAF works today.

Here is just a snip of the description of how DPAF works. The first focus detection method is the phase detect portion, followed by contrast detection. see patent JP2001350193 It does not need to have AFMA because the contrast detect makes sure the image is in sharp focus.

"A first focus detection means that detects a focus state of the aforementioned photographing optical system with a phase difference detection method or an active system.
A second focus detection means which detects a focus state of the aforementioned photographing optical system with a contrast detection system."




Oct 19, 2017 at 06:39 PM
MintMar
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p.1 #16 · p.1 #16 · Will micro adjustment affect both kinds if autofocus?


My take is that most probably the LV AF algorithm picks on something else than the manually focusing human wanted.


Oct 20, 2017 at 07:15 AM
Andrew J
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p.1 #17 · p.1 #17 · Will micro adjustment affect both kinds if autofocus?


That's why you zoom to 10x before using LV AF.


Oct 20, 2017 at 07:23 AM
scalesusa
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p.1 #18 · p.1 #18 · Will micro adjustment affect both kinds if autofocus?


MintMar wrote:
My take is that most probably the LV AF algorithm picks on something else than the manually focusing human wanted.


It depends on the camera, the 5D IV allows for a smaller liveview focus area which is less likely to catch a unwanted subject.




Oct 21, 2017 at 08:38 PM





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