CHG_CANON Loc: the Windy City

The EOS R5 will change how we think about mirrorless, how we think about photography, how we think about life.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

The newer Canon R5 can auto focus with any lens that has a minimum opening up to f11. So, any lens with an minimum opening from 1.2 to 11 will auto focus on a Canon R5.
I believe Canon did this to handle their new 800mm f11 lens.

Architect1776 Loc: In my mind

Except the Canon R5 and R6 do f22 with no problem.

JRiepe Loc: Southern Illinois

Correct. I used to shoot a lot of macro and wondered why most macro lenses needed such a wide aperture when most shots are taken at much smaller apertures to achieve greater DOF. That is until I learned that the aperture closes down only when the shutter release button is half way depressed. The wide maximum aperture results in a brighter viewfinder to aid focusing.

StanMac Loc: Tennessee

That might apply if you’re using a stopped down third party lens in manual mode that doesn’t link to your camera’s aperture function?

Stan

CPR Loc: Nature Coast of Florida

Auto Focus needs a certain amount of light to function - the lens aperture is held open but an extender reduces 2 stops without the connections to hold it open during focusing??

Dik

RF 600 & 800 f/11 lenses have no aperture settings, always wide open. Canon Tele-Extenders have electronic connections for aperture and focus.

Architect1776 Loc: In my mind

With a 2X TC the aperture is effectively f22.
R5 and R6 AF works great at f22.

robertjerl Loc: Corona, California

OK, if I win the lottery or VA suddenly realizes I was entitled to 100% disability instead of 40% and sends me a "We're sorry" check back to when I started collecting I may buy an R series and a few lenses. But what would greatly test my GAS resistance would be an R7 replacement for my 7DII with about 20-24MP. My 90D with 32MP is TOO SENSITIVE to motion blur at anything below "Oh my God that is a fast SS". Even with sitting birds and my 150-600 on a tripod it seems like if I just look at the camera too hard I get faint motion blur.

User ID

AF has no “ceiling”. It works where it works and there are variables beyond the “collective wisdom” evidenced on this site. Buckle up, enjoy the ride. It could be a rather bumpy road, all the way to page 12.

lamiaceae Loc: San Luis Obispo County, CA

I think some vintage Nikkor lenses act like that on some Nikon cameras. It is not an issue for everyone or Pentax users. There are all sorts of specific issues reported that are often not true or general.

amfoto1 Loc: San Jose, Calif. USA

Autofocus needs some level of light to be able to focus. Newer cameras, especially mirrorless, are a whole lot better and able to focus in lower light levels. But they all still need some light to work.

As noted in a previous response, this has almost nothing to do with the aperture you select to make an exposure (or that the camera chooses for you, if using an auto exposure mode).

The apertures in lenses used on SLRs, DSLRs and mirrorless are held wide open until the moment of exposure, and then they only stop down momentarily.

So the "restrictions" on autofocus really only apply to a lens' maximum aperture. Those are part of the lens' label, such as a 50mm f/1.8, a 300mm f/4, a 24-70mm f/2.8 or a 70-300mm [/fl3.5-5.6[/i]. This is the lens' "speed" while the aperture is being maintained wide open during focusing, metering, etc. Notice that one of the examples is a "non-variable" aperture zoom, where the same max aperture is maintained across the entire focal length range. The 70-300mm example, on the other hand, is a variable aperture that changes as the lens is zoomed to longer focal lengths. Many zooms today are this type. Non-variable aperture zooms tend to be larger, heavier and more expensive.

The "problem" usually only occurs if you combine a teleconverter with a lens. A 1.4X teleconverter "costs" one stop of light. A 2X teleconverter reduces light by the equivalent of two stops.

So if you add a 1.4X to the 300mm f/4 lens example above, it "becomes" an effective 420mm f/5.6 combination. But if you add a 2X teleconverter to it that makes for an effective 600mm f/8 combo.

Older camera AF systems were commonly "f/5.6 limited", meaning that the 420mm f/5.6 combo would be able to focus, but the 600mm f/8 combo cannot AF on those cameras. (Note: Teleconverters also don't make much sense to use on shorter focal length lenses and may cause too much image quality degradation to be worth using.)

Newer cameras have one or more AF points in their array that are "f/8 capable" and would be able to autofocus both those combinations... at least to some extent. It may only be possible using a single AF point or a select few. And it may focus slower and/or be more inclined to "hunt". To some extent AF capabilities and performance also depend upon lighting conditions, subject contrast and other factors.

So, generally speaking you will be fine with most DSLRs so long a lens has a max aperture of f/5.6 or larger (i.e., a lower number, since this is a fraction). There also are some lenses that have f/6.3 max apertures, which "fool" the camera into focusing.

More and more DSLRs are now able to focus f/8 with reasonably good success. Some will even be able to work when you have as little as f/11 equivalent, so long as lighting conditions are good.
It varies by brand and model, too. For example, Canon has "hard limits" built in. When their cameras "recognize" a lens/teleconverter combo that exceeds their rated capability, the AF system turns off. OTOH, the last couple generations of Canon DSLRs have improved from f/5.6 limited to f/8 capable. Now only their most entry-level models are still f/5.6 limited (REbel T7 and SL3 models in the US, known as EOS 1500D, 2000D and 250D in other parts of the world). All other Canon DSLRs have at least some f/8 capabilities.

Some other brands might not have a built in limit, may "try" to focus, but also may struggle.

Now, most DSLRs are designed so that light reaching their AF sensor array has to first pass through a semi-transparent mirror. There's some light lost to that mirror, which is part of the reason for their limits.

For this reason mirrorless cameras - which have no mirror and have their AF sensors embedded directly in their imaging sensor - "see" light more directly and with no loss, and often are able to autofocus in even lower light conditions. They generally have no problem at f/8 and, in most cases, f/11 equivalent. In reasonably good light they may even be able to autofocus beyond that point to f/16 equivalent. As a result, lenses for mirrorless cameras are being offered with f/7.1, f/8 and even f/11 max apertures. Canon has recently introduced very compact 600mm f/11 and 800mm f/11 lenses. They can even be used with a 1.4X teleconverter, making for an effective f/16 max aperture, and the R-series cameras are able to autofocus very well.

Architect1776 Loc: In my mind

And with 2X at f22.