[Arthur Macmillan]

Go search for "Lensrentals Autofocus Reality" and read every single part.

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Also yeah, mirrorless have many advantages there.

Obican, nice reference article(s).  I like Roger Cicila's summary of MFA and dslrs, but of course pay attention to the qualifications in his summary:

"The conclusion is pretty obvious: If you want to shoot wide aperture prime lenses and you don’t want to use microfocus adjustment, you just refuse to cope with reality."

I've always be fascinated with ultra fast lenses, and yet I only have one or two that are not old film era manual focus lenses.  I say one or to not because I can't remember which lenses I own.  Rather because I am still not sure of what qualifies as ultra fast.  Since Roger did not calibrate the 50mm f/1.4 I'm not sure if he checked that calibration and was happy with it, thinks the inferior focus motor makes calibration that still leaves the lens incapable of accurate focus, or (least likely) that 50mm at 12 feet and F/1.4 was maybe not a narrow enough DOF.  

Here is what the depth of field is according to the DOF calculator on this site:
https://www.dofmaster.com/dofjs.html

d =12 feet, lens is 50mm, f/1.4, and camera is Canon 5D Mk II:
DOF = 1.47 feet, where in focus starts at 11.3 feet and ends at 12.8 feet.

This might seem surprising or boring to you depending on what you like to photograph.  But I just love stuff like this, and if I got it wrong, please correct me!  Now for comparison we got to the 50mmFf/1.2L,

d=12 feet, lens is 50mm F/1.2L on 5D Mark II:
DOF = 1.24 feet.  In focus starting at 11.4 feet and ending at 12.7 feet.

Of course, what Roger Cicala, whom I respect immensely is telling us that the Imatest is able to perceive sharpness well beyond what is considered in focus by the calculator.  The calculator says in focus or not.  The Imatest can compare how sharp an image is.  But my point is to wonder do I have a fast lens that needs MFA adjustment?  Well, I have the 135mm F2L USM.  A pretty old design with no OIS, and opinions of it range from the best bargain in the EF lineup to, well, I don't need to repeat words that are so far gone.  For fun:

d=12 feet, lens is 135mm F/2L USM:
DOF = 0.28 Feet.  In focus starting at 11.9 feet, and in focus ending at 12.1 feet (this is how they round off).

So, anyway, by the standard that people often use you might say that I don't have a single ultra fast lens.  But in my opinion I probably have at least seven.  Moreover at the distances that these lenses are normally used at I don't consider a 50mm F/1.4 MF lens hard to focus at all.

Still, I need to finish reading the series of articles, and do love them so far.  I just find for me, it is actually not that easy to see focus problems with a 50mm lens, where you are likely to see them easily on longer lenses.  Again, I know that the testing system makes that not relevant for his purposes, it does make me wonder why some people worry about real world results with short lenses.

-Mac