gvarner Loc: Central Oregon Coast

I just saw a post that said most digital cameras have an auto focus ceiling at f11, can't focus above that or have difficulty focusing. I’ve never heard that before and am wondering if it’s true. Your knowledge and experience would be appreciated.

Rongnongno Loc: FL

Err... Auto focus is done with the lens aperture wide open. Your aperture setting is applied only when you capture the scene, so it does not influence the camera focusing system.

On the other hand, your aperture choice may influence the sharpness of your image (something about a lens optimal aperture and focal plane distance)...

Longshadow Loc: Audubon, PA, United States

Saw where?
Link?
Source of info?
Under what conditions?
Are they selling snake oil also?

gvarner Loc: Central Oregon Coast

It was an answer posted to this inquiry by sergio, "Your advice on Canon R5 with RF800 lens and 1.4x Extender". The comment said F8, not F11. My mistake.

Rongnongno Loc: FL

After reading the thread...

This is about using an extender that might create an interference with the lens autofocus.

All bets are off.

Longshadow Loc: Audubon, PA, United States

Maybe limited by the extender? Your initial question did not contain that information.
I would ask the poster on what that information is based,
not UHH, with partial information....
The poster might be able to provide a link explaining it.

Longshadow Loc: Audubon, PA, United States

BebuLamar

It's true! It used to be f/5.6 but newer AF system can handle f/11. The Canon R series can AF the 800mm f/11 lens quite well.

Longshadow Loc: Audubon, PA, United States

Same problem with focusing during stop-down metering.
But no conditions or circumstances were given in the original post,
just a limit stated.

jeep_daddy Loc: Prescott AZ

What they were probably referring to is that autofocus using a teleconverter, also known as a doubler or extender, will cause your settings to lose a stop or 2 stops. What that means is that if you have a lens that opens up to (say) f/5.6, when you put a 1.4x on it will only open up to f/8 because you've lost a stop of light. This isn't a problem for most of the newer camera bodies with a modern lens, but if you put an older lens on an older body and then use the 1.4x teleconverter, it will NOT autofocus. For instance, I used to have a Canon 7D (the original) and the original 100-400 Canon lens. When I tried the 1.4x Canon teleconverter with that combo, it would NOT autofocus. But, today I have the newer 7D Mark II, and the newer 100-400 Mark II lens, with the 1.4x teleconverter it has no problem autofocusing but I can only use a single focus point.

If I were to use a 2x doubler, my f/stop would be a minimum of f/11 now. I'm pretty sure that my new setup will autofocus but it will be extremely slow and it will not be very accurate. This is because it's lost so much light that the camera can't do it's magic to autofocus. As you look thru the viewfinder, you can't really see this, but as soon as you push the shutter button your camera has less light to work with.

I hope this is what you were reading about.

Longshadow Loc: Audubon, PA, United States

PHRubin Loc: Nashville TN USA

Yes - but you must realize that it pertains to the lens' wide open aperture. f/8 is the limit for many cameras. If an extender is used, that must be taken into account.

robertjerl Loc: Corona, California

That refers to the maximum aperture of the lens wide open. Which is the way AF works, focus wide open, then shut down to the selected aperture when the shutter is activated.
Many cameras the limit is f/5.6, then cameras that did f/8 came along and now a lot of the new mirrorless models can handle f/11. Which is why Canon came out with some RF mount very long telephotos with a max of f/11. And they are a lot cheaper(also smaller and lighter) than the older models that have much wider maximum apertures.

A while back I skimmed an article (which I then lost track of) about some guys who managed to get a high end mirrorless (Canon R series???) combined with a lens that had an extender on it to AF at f/22. I wish I could find it again so I could read the whole thing to find out how they did that.

tcthome Loc: NJ

Probably linked to the new Canon long lens for the R series cameras.

Dik

I have had and used the Canon 800 f/11 + 2x RF extender (f/22) on both EOS R and R5. AF worked fine.