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Dot-Tune: Autofocus Fine Tuning in under 5 minutes
  
 
Zenon Char
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p.38 #1 · p.38 #1 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Now I'm confused. That link makes a reference to the 7D2. The 7D2 does not even offer Dual Pixel RAW. I guess PDAF is a separate function we can't turn off or on I was not aware off?


Oct 09, 2017 at 03:48 PM
Zenon Char
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p.38 #2 · p.38 #2 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Well you learn something everyday. I have never worn out the video button on my cameras as I never use it and I rarely use LV.

https://photographylife.com/what-is-dual-pixel-raw-in-the-canon-5d-mark-iv

This is all new to me but it seams you just MFA the traditional way for back or front focus. PDAF just uses two readings to fine tune while in video mode or tracking subjects in LV. I realize I could be wrong.



Oct 09, 2017 at 04:01 PM
Zenon Char
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p.38 #3 · p.38 #3 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


gschlact wrote:
In reading the article, it says that DPAF uses Phase Detect AF.
The feature you mention for post processing focus adjustment with the huge files I thought was called something else?
So the question I ask boils down to... If DPAF=PDAF
a) how do we get Contrast Detect AF in Live View instead of the dpaf/PDAF?
b) is dpaf PDAF different from the focus screen for non live view?

Contrast Detect af is used in dot tune to establish the proper AF prior to turning af on the lens to manual to start start tuning of MFA values.


Yes it says PDAF uses phase detect in LV tracking subject and for video. I think that if you want to be in Contrast Detect you need to be in one shot. If you are tracking someone then you are in AI Servo and I guess this is the tracking part.

I don't know about part B. Does PDAF only apply to LV when in AI Servo and video or also for one shot phase detect as well?

As I stated on my other 2 posts, I think you can only MFA the traditional way which is for phase detect. If LV or video utilizes phase detect it must use the MFA values entered. You would think that Canon would have thought of that otherwise a lens and mirror assembly needing +-12 wouldn't be sharp.

Maybe someone who knows more about this will help out.



Oct 09, 2017 at 04:27 PM
Zenon Char
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p.38 #4 · p.38 #4 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Forgot to mention that Dot Tune starts out using LV for contrast detect AF accuracy or you can also use manual focus if you want to. Then you take it out of LV and which uses phase detect to tune MFA values.


Oct 09, 2017 at 04:42 PM
 

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Zenon Char
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p.38 #5 · p.38 #5 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


In the Go Live section of the document it does not distinguish between One Shot or AI Servo. Seems like it uses both contrast and phase detect when in LV. Contrast is accurate. Phase is the one that can be out. I think a few ticks off centre is OK but like I said if out 12 one way or the other there may be issues. Not sure but logic says if the two are competing that much it would show unless Canon uses contrast as the primary and phase as a confirmation only. Same as flash. While the Canon system gathers distance information it is a reference it always goes by the pre-flash information regardless of what distance info it gets. I don't know about contrast ads phase.

I also think that if there was something we needed to know Canon would have said so. There have been no updates to MFA procedures since the release of PDAF.

Thanks for brining this up. Interesting.



Oct 09, 2017 at 05:05 PM
Zenon Char
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p.38 #6 · p.38 #6 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


I was wondering about the mirror. How does phase work without it and I figured there must another smaller mirror or something. Still have not found out expect for this.

But if there’s one phrase that sums up the evolution of the EOS 70D – it’s “Dual Pixel CMOS AF”. It sounds like rocket science, but it is really simple to explain. DSLR cameras focus use phase detection to quickly achieve focus using a beam splitter through a reflex mirror. In Live View or movie recording mode, the mirror is flipped up and the autofocus switches to a hybrid of phase detection and contrast detection. Because of the small number of sensor pixels for detect contrast detection, such hybrid AF usually lag behind pure phase detection AF.

https://petapixel.com/2013/10/28/review-canon-eos-70d-sets-phase-detection-stun/

So outside of the normal phase detection MFA I have not heard of any method to MFA this hybrid system. Contrast detect is pretty basic but what does it use for phase detect when there is no mirror and why is it more accurate than the standard phase detect method. I'm assuming it is more accurate.



Oct 09, 2017 at 07:57 PM
Zenon Char
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p.38 #7 · p.38 #7 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Both the last post and this one are for the 70D. I don't know if Canon changed anything with the newer releases regarding this.

Note, though, that I said phase detect operation, as that's only part of the process the EOS 70D uses in live view AF, at least for still-image focusing. Part of the reason the 70D's Dual Pixel AF isn't as fast as the conventional separate-sensor approach is that the 70D only uses Dual Pixel technology to achieve rough, initial focus; it then switches to contrast-detect focusing to check focus accuracy and, if necessary, fine-tune focus.

http://www.imaging-resource.com/news/2014/02/27/canon-dual-pixel-cmos-af-autofocus-secrets-of-the-canon-70d-explained



Oct 09, 2017 at 08:08 PM
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