5D4: regular AF vs live view Af

[jeanluc]

Just wondering if any 5d4 owners have tried a comparison of the regular AF vs AF using live view.

In a previous post, I noted that my first copy of the 5d4 had issues with the AF......specifically the regular AF was not working properly (ie not nearly as sharp as when I focused with live view, which was tack sharp each time).

Camera was on a tripod, shooting at my Spyder Lenscal AFMA target.

That camera went back (B and H returns work GREAT BTW, can honestly say you really will never have any problems with them), and I got another one.

So of course I tried the same comparison, using my 70-300L and my 100L macro.

This one works much better, there is very little if any difference between the 2 AF methods most of the time.

Using the 100L macro, there is no difference between regular af and live view af.

Using the 70-300L, the live view AF is a little better most of the time. But not anything like the other camera.

When using the live view AF, I was magnifying it before focusing.

I was wondering if one should expect the live view AF to be more accurate or not. Granted when using it I am magnifying it, and the 5D4 does have dual pixel live view af.

I was hoping some of our tech-savvy forum members would have an opinion on this, and if anybody else who has a 5d4 wants to try the test, I would love to hear your thoughts!

I suspect my original 5d4 had an issue with the af, but was surprised that the live view is always as good as, and even better that regular AF. maybe dual pixel is just that good.

Thanks for any help/info!

 

[AlanF]

Do you AFMA your lenses? If you don't, and the AFMA differs significantly from 0, then they won't be sharp and liveview should be. Also, liveview doesn't suffer from shutter shock/mirror slap and will be sharper in the 1/100s region relative to AF even when the AF is well focussed.

 

[Mikehit]

Yes, I would expect LiveView AF to be moe accurate and more consistent than 'normal' AF. The reason for this is that LiveView AF is reading the accuracy of AF from the data on the sensor itself whereas 'normal' AF is using an algorithm to judge focussing on a beam of light that has been split off from the main light path with the assumption it will be 'in focus' on the sensor.

This is Canon's own description:
http://cpn.canon-europe.com/content/education/infobank/autofocus/autofocus.do

Apparently AF is adjudged to meet quality standards if the point of actual focus is within the DOF of the subject (it sounds a bit high to me but that is what I read), so as Alan says, you can only really judge it if you have done microfocus adjust.

 

[Besisika]

Cannot justify it technically, but yes live view is more accurate than viewfinder for me on 1dx ii. When shooting with the 85 1.2 I use exclusively live view, in particular portraiture.

 

[neuroanatomist]

Apparently AF is adjudged to meet quality standards if the point of actual focus is within the DOF of the subject (it sounds a bit high to me but that is what I read), so as Alan says, you can only really judge it if you have done microfocus adjust.

To clarify, the standard precision AF points are specified to be accurate to within one depth of focus at max lens aperture, and the high-precision AF points (center point on most bodies, row of 5 points on recent 1-series and 5-series bodies) are specified to be accurate within 1/3 the depth of focus at lens max aperture.

Note that depth of focus ≠ depth of field. Depth of focus is the sensor-side counterpart of depth of field, is measured in µm, and depends mainly on lens aperture with very little dependence on subject magnification. OTOH, depth of field is highly dependent on subject magnification (whether you factor that in as subject distance or focal length).

 

[Mikehit]

Thanks for the clarification, neuro.

I looked a bit further and for anyone interested came up with this which made sense to me (the it in bold is the one I can visualise more easily) :

The phrase depth of focus is sometimes erroneously used, to refer to the depth of field (DOF), which is the area in front of the lens in acceptable focus, whereas the true meaning of Depth of focus refers to the zone behind the lens wherein the film plane or sensor is placed to produce an in focus image.

Depth of focus can have two slightly different meanings. The first is the distance over which the image plane can be displaced while a single object plane remains in acceptably sharp focus;[1][2] the second is the image-side conjugate of depth of field.[2] With the first meaning, the depth of focus is symmetrical about the image plane; with the second, the depth of focus is greater on the far side of the image plane, though in most cases the distances are approximately equal.

Where depth of field often can be measured in macroscopic units such as meters and feet, depth of focus is typically measured in microscopic units such as fractions of a millimeter or thousandths of an inch.

https://en.wikipedia.org/wiki/Depth_of_focus

Good ol' wikipedia

 

[YuengLinger]

With my 85mm 1.2 L AFMA'd, I'm finding sharpness the same in both AF and Live View.

I will say that the speed of Live View compared to the 5DIII actually startled me. I couldn't believe my eyes.

But doing a scientific comparison is too much of a challenge for me. LiveView is sharp and quick. Viewfinder AF is incredibly fast and much, much more accurate than I ever got from my 5DIII.