Will a Nikon Autofocus at an Aperture of Less Than f/5.6?

I often read discussions on forums and social media by someone who has “read somewhere” than a Nikon cannot autofocus a lens at an aperture smaller than f/5.6. Is this true? Absolutely not!

Fact: Older Nikons may not autofocus reliably with a lens having a maximum aperture smaller than f/5.6. That may sound bad, if you assume that it means the camera will not autofocus reliably when the aperture is closed down to f/5.6. That is not what Nikon is saying! Instead they are telling us that autofocus may not work reliably on older Nikons with a lens having a maximum aperture of f/5.6, with the emphasis on the word maximum.

Max and Min Aperture

Maximum (f/2.8) and Minimum (f/16) Aperture

“Maximum aperture” means the largest aperture (biggest hole) the lens can possibly have when it is wide open. A lens autofocuses with the aperture wide open and then stops the lens down (closes the aperture to a smaller hole) only at the very moment of exposure. If you are using a lens with a maximum aperture of f/5.6, the widest the lens can ever open is f/5.6, which does not provide enough light internally for many older Nikons to autofocus reliably.

It is critical you understand that I am not talking about using a standard Nikkor lens at f/5.6, f/8, f/11, f/16 or a smaller aperture opening. All AF Nikons will autofocus with an AF lens at any aperture the lens supports. They can do that, again, because autofocus happens at maximum aperture, which on even low-cost Nikon lenses is usually about f/3.5. Maximum apertures on many prime lenses are f/1.4 or f/1.8. And on pro zooms the maximum aperture is usually f/2.8 or f/4.

Therefore, even an older Nikon will autofocus on normal AF lenses all the way down to the smallest aperture because the actual autofocus happens at maximum aperture (largest hole), which on most lenses is bigger than f/5.6.

When you add a teleconverter to a slow telephoto lens, the maximum aperture can sometimes drop below the f/5.6 barrier, making autofocus difficult or impossible on older Nikons.

Newer Nikons, such as the D7200, D7100, D600, D610, D750, D800, D800E, D810, D4, and D4S, all support lenses having a maximum aperture of f/8 with a limited number of the 51 (or 39) available AF points (usually 11, 7, or 1 AF point). Newer Nikon cameras have a special arrangements of AF points that can autofocus on lenses with a maximum aperture all the way down to f/8. That makes your newer Nikon a special and valuable camera if you want to use telephoto lenses with teleconverters.

Keep on capturing time…

Darrell Young

Darrell Young is an active member of the Nikonians User Community, Nikon Professional Services (NPS), Professional Photographers of America (PPA), North American Nature Photography Association (NANPA), and the author of 15 photography books from NikoniansPress through Rocky Nook, including Beyond Point-and-Shoot, Mastering the Nikon D610, Mastering the Nikon D800,Mastering the Nikon D7100, and Mastering the Nikon D810, to name a few. He’s been an avid photographer since 1968 when his mother gave him a Brownie Hawkeye camera.

His website, www.PictureAndPen.com, was created to support the readers of his educational books, photography students, and clients. Visitors to his website will find articles and reviews designed to inform, teach, and help you enjoy your photographic journey.

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2 Comments

  1. Hi Darrell,

    4 years ago I purchased the D5000 and shortly after that I purchased your book “Mastering the Nikon D5000” from Amazon which provided immense help in getting the most out of my camera.

    I have upgraded to the D5500 and wonder if you have any plans to write a book in the style of the one I used so extensively over 4 years? I really hope so.

    Maybe you could give me some indication as to when this book might become available if you decide to write it.

    Yours sincerely

    Kevin from Dublin Ireland.

  2. Hi mr. Young
    I have read that my D7100 & D750 when using my Tamron 150-600 F5-6.3 VR are using only 11 AF points with 9 horizontally and 3 vertically and the one at the center is the only one used as cross-typed. In such a case the 51/15 AF points are useless, and I suppose a low-cost D5500 will do as good focusing on a bird in flight. If its true its very deceiving. Please comment.
    regards
    Luc

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