Why not Electronic full-time MF

[pedz]

This is most likely a rhetorical question.  I was out with my RF 800mm f/11 lens and discovered that Electronic full-time MF doesn't work.  And, according to the info page, that's true.  I tried my RF 24-240mm and it didn't work either.  Finally I found the page and tried the RF 100-500mm and it worked... so I wasn't going crazy. 🤪. Note that this is when the auto focus mode is set to servo.  They both work when set to one-shot.  (And the Electronic full-time MF is set to ON.)

The question is: why?  I believe that it is not a physical issue -- since they both work in one-shot mode.  I realize that the easy answer is the firmware just doesn't allow it but...  bummer!!!!

This really is important when shooting small birds.  The auto focus will get "stuck" on a near or far object such as a twig, leaf, or branch and not focus on the bird sometimes -- especially when the bird is in foliage.  The easy cure for this is to rotate the focus ring a bit to get the focus off of that object.

I hope Canon will start enabling this feature on all of the lenses.

[SignifDigits]

Sorry if I missed it but did you say what camera that you are using?  The R6 Mark 2 allows the option to toggle on the 200-800 and the 24-240.  I don't know about the 800mm as a don't have it to test.  

[pedz]

I was testing yesterday with the R5 Mk II but I also have an R1 and I think that when I first discovered it, it was with the R1 but I am not sure.  It is interesting that it works with the 24-240.  Are you sure it does even in servo mode?

Also, just to clarify, I can set it to "On".  It just doesn't function.  I turn the focus ring and nothing happens.

[SignifDigits]

The older I get the less certain that I am of anything!  Thanks for clarifying, I was just looking at "on" in the menu and assuming that it worked.   Of course you are correct.  I was in single-shot and in servo the manual focus on the 24-240 has no effect on focus.  The 200-800 DOES manual focus in servo mode, though.  The marketing reason to not support the 800mm and the 24-240mm would be to get us to upgrade to the 200-800 (an upgrade I do not regret, btw).  Technical reason might include them running on 5, nearly 6, year-old firmware.

[ebiggs1]

"I believe that it is not a physical issue ..."

Yes, it can be. Some lenses don't uncouple the AF mechanism and that can lead to unwanted clashing of the internals.

[normadel]

Forgive my asking.....What is electronic about Manual Focus? 

[Waddizzle]

I reas the problem as you cannot manual focus while the AF is active.  This can be a problem for lenses that focus by wire, STM.

I program the rear [AF-ON] button as [AF-OFF].  I find this configuration to be very useful in subtle ways.

I am on the road, so I can’t test this idea for a couple of days.  If I press [AF-OFF{, this wakes up metering, but with AF disabled. Can I refocus my STM lens at this point.

[pedz]

The focus ring on the lens operates electronically rather than mechanically.  For example, on most RF lenses, you can turn the focus ring in one direction forever.  When the camera is off, as another example, the focus ring can be turned and no part of the internals move.  The ring is basically just a digital input that is read by the camera's processor and then the processor sends signals to the lens to change its focus.  Another example, in custom controls (6th element of the menu) tab 2 of 4 item 4 allows you to reverse the sense of the focus ring.  Even if the lens is set to MF mode, the ring is just an input device and not mechanically connected to the focus mechanism of the lens.

In the current firmware of the R5 Mk II there is a setting that is at the bottom of the 6th tab (of 7) in the AF menu (search for Lens electronic MF -- my browser doesn't seem to scroll to it properly).  But, on some lenses it doesn't work as well as it does on other lenses.  In particular, with the mode is set to servo, there is no way to manually adjust the focus on some of the lenses.