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Rudy Winston
Rudy Winston

Rudy Winston has over 17 years experience with Canon USA's Pro Products team, and has been responsible during that time for training Canon's staff on new products, creating presentations for customers and dealers, numerous writing projects, and providing technical assistance to professional and amateur photographers.

What's new: EOS 80D - AF at f/8 max. apertures

February 18, 2016

The Canon EOS 80D offers enough performance value and “bang for the buck” that to many advanced amateur shooters, it’ll be a compelling possible purchase.  One area that more and more experienced D-SLR shooters are asking about is use of telephoto lenses with Canon EF tele extenders, and the EOS 80D opens some new ground here.

The 45-point AF system in the EOS 80D adds the ability to focus at effective maximum apertures as slow as f/8 — a big departure from previous mid-range EOS cameras, where AF was possible only until maximum apertures of f/5.6 were reached.  This is going to open a lot of potential to wildlife and nature photographers, as well as sports and other shooters who are looking for ways to leverage telephoto imagery.  Coupled with the camera’s 7 fps shooting capability, this makes the EOS 80D a very cost-effective option for good performance along with relatively compact size.

Tele extenders certainly open up even more possibilities to use the gear you currently own to get impressive pictures. Here, a 400mm lens combines with an EF 2x tele extender, doubling its focal length — without changing the lens’s minimum focus distance. The result can be powerful images of relatively small subjects, like the birds shown here in this uncropped image. With the new Canon EOS 80D, even more AF possibilities exist (vs. previous mid-range EOS cameras) when effective maximum apertures get slower than f/5.6.
What exactly is f/8 autofocus?

We’ve explored this question in previous articles on Canon USA’s on-line Digital Learning Center, but it bears a quick repeat, especially since a camera like the EOS 80D will likely attract many users new to either D-SLRs in general, or new to mid-range cameras with these kinds of advanced features.

The AF systems in the vast majority of today’s digital SLRs, including all Canon EOS models to date, are designed to work with lenses of varying maximum apertures.  This holds true for wide-aperture, “fast” lenses with low f-numbers (think of lenses like the EF 50mm f/1.8 STM, a high-end lens like the EF 85mm f/1.2L II USM, or a zoom like the EF 70–200mm f/2.8L IS II USM).  And, with lenses having smaller maximum apertures, the AF system continues to function — until you reach lenses where f/5.6 is the widest possible aperture.

Canon’s AF system can accommodate virtually all EF or EF-S lenses in the system with maximum apertures up to f/5.6.  In fact, as of early 2016, there are no lenses in the Canon EF or EF-S system with maximum apertures slower than f/5.6.

But that changes if you add a tele-extender to any compatible Canon lens.  We’ve written a pair of articles that detail how Canon tele extenders operate, and about the issue of light loss when extenders are used.  These articles can be found here:

The key point here is that there’s an inevitable light loss of one stop in effective maximum aperture if a 1.4x extender is combined with a compatible Canon EF telephoto lens, and a two-stop light loss if a 2x tele extender is used.  These are unavoidable physical losses in light transmission, and cannot be overcome optically.

In real life, this means if you have a lens with an f/4 maximum aperture (example — the EF 70–200mm f/4L IS zoom lens), if you add a 1.4x extender, its effective maximum aperture becomes one stop slower — f/5.6.  And, if you add a Canon-brand EF 2x extender, it now slows down to an effective maximum aperture two stops slower — now it’s f/8.

The bottom line is that users who contemplate using tele extenders have always had to consider whether adding that extender made their lens cross that f/5.6 maximum aperture threshold, and if so, many previous cameras (such as the previous EOS 70D model) would shut down AF completely.  But the new EOS 80D’s updated AF system can now provide AF if the maximum aperture is f/8 or wider.

Reminder: you’re free to shoot pictures at ANY lens aperture!

Just to clarify:  AF systems on digital SLRs are only concerned with what the maximum effective aperture of a lens, or lens + extender, is.  You’re completely free to take pictures at smaller apertures, like f/16 or f/22 if you want the effects of a small opening, and this has no impact on the lens’s ability to focus!  With the EOS 80D, as long as your lens + extender’s maximum effective aperture is f/8 or wider (in other words, a lower f-number), AF will function as described below, and you can take actual pictures at any final shooting aperture you want to with no further effect on AF performance.

The reason?  All AF operations occur with the lens in a wide-open position, regardless of the aperture you’ve set manually, or that the camera may set automatically when actual pictures are taken.  This is standard operating procedure for AF with all Canon EOS digital SLRs, when focusing using the eye-level viewfinder and the camera’s independent AF sensor.

AF at the center point, at f/8 with tele extenders

With most combinations of an EF telephoto lens and a Canon-brand EF 1.4x or 2x tele extender, AF remains possible at the center AF point if the maximum aperture is slower than f/5.6, down to f/8.  A few popular lens + extender examples of this:

  • EF 70–200mm f/4L (IS and non-IS versions) + Extender EF 2x (versions I, II, and III)
  • EF 100–400mm f/4.5–5.6L IS (original version) + Extender EF 1.4x (v. I, II and III)
  • EF 300mm f/4L (IS and non-IS versions) + Extender EF 2x (versions I, II and III)
  • EF 400mm f/5.6L + Extender EF 1.4x (versions I, II and III)
With most combinations of a (compatible) Canon EF telephoto lens and a Canon-brand EF tele extender, if the maximum effective aperture is f/8 (or faster), you can get AF at the center AF point, as indicated here. This transition to center-point AF happens immediately when an f/8 maximum aperture is detected by the EOS 80D; no adjustments aside from attaching the tele extender are needed from the photographer.

Nearly all compatible lens + extender combinations with resulting f/8 maximum effective apertures will work in this manner, so it’s not limited to the lenses mentioned above.  This includes all of Canon’s “big white lenses,” such as the EF 500mm f/4L or 600mm f/4L lenses, if combined with a tele extender that renders the effective maximum aperture between f/5.6 and f/8.

However, there’s an exciting new possibility if you combine two of Canon’s latest, high-end tele zoom lenses with the most recent Version III EF tele extenders!

Focus with 27 AF points, at f/8, with newest tele lenses + extenders

For technical reasons, two of the latest super tele zoom lenses from Canon can provide added AF coverage, if they’re combined with the most recent Version III Canon EF tele extenders.  Twenty-seven AF points are available, as shown here:

For technical reasons, Canon’s most recent Version III EF 1.4x and 2x tele extenders can combine with the latest super-telephoto lenses to provide even broader coverage at the EOS 80D’s AF sensor. These two lens + extender combinations allow AF at these 27 AF points. And, users can freely manually select any one of these AF points, as well as change to different AF Area options.

Lenses providing this broader 27-point coverage at f/8 effective maximum apertures with the EOS 80D are:

  • EF 100–400mm f/4.5–5.6L IS II + Extender EF 1.4x III
  • EF 200–400mm f/4L IS Extender 1.4x lens + Extender EF 2x III (built-in extender not used)
Summary

For years, photographers have grown used to assuming that if they wanted additional features like the ability to use autofocus with lenses slower than f/5.6, that they needed to turn to advanced, high-end digital SLR cameras.  Canon engineers have begun to listen to the growing requests from our customers who want the ability to continue to use AF, without requiring big, heavy and expensive super-telephotos with wide apertures to achieve this if they want to add a tele extender.

The EOS 80D’s new 45-point AF system is a strong testament to this.  It provides AF at the center AF point with almost all combinations of compatible Canon EF telephoto lenses and Canon-brand tele extenders with f/8 (effective) maximum apertures.  And, it expands this to an outstanding 27 available AF points at f/8, with the two new lenses mentioned immediately above, if combined with the latest Version III tele extenders.  Even if you’re using an older lens or extender, though, the EOS 80D will make it possible to get more out of your gear, and at a much lower cost of entry, than the higher-end cameras that would have been required previously.

The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.

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