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This is a follow-up to Why does Canon and Nikon limit or disable autofocus beyond certain f-numbers? I'm doing this to separate the AF aperture requirements from the linked question above. My goal here is to create a canonical answer for Canon AF aperture limits, with complete information for every Canon EOS model since the EOS D30.

What apertures are required for Canon EOS DSLR cameras to autofocus? What apertures are needed to enable cross-type and/or high-precision autofocus?

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3 Answers 3

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TL;DR answer

In general, Canon DSLRs require a maximum aperture of at least f/5.6 to autofocus. Depending on the camera model, and with some exceptions, a maximum aperture of at least f/2.8 or f/4 enables cross-type and/or high-precision focusing. EOS-1 series cameras and the EOS 5D Mark III (with the latest firmware) can autofocus at f/8, but only with the center point.


Definitions

  • A horizontal-sensitive point or vertical-sensitive point is an autofocus point that can detect horizontal or vertical lines, respectively. A horizontal-sensitive point cannot detect vertical lines, and a vertical-sensitive point cannot detect horizontal lines.
  • A high-precision sensor is an autofocus sensor that is capable of focusing within 1/3 of the depth of field of the lens, instead of simply within the depth of field. These sensors require faster maximum apertures, typically at least f/2.8, in order for them to work.
  • A cross-type point is an autofocus point that can detect both horizontal and vertical lines simultaneously. Depending on the camera model, the maximum aperture may need to be at least f/2.8 or f/4 for a point to be cross-type, because the vertical-sensitive part of the AF point is a high-precision sensor.
  • A dual cross-type point is an autofocus point that can detect diagonal lines as well as horizontal and vertical lines. The diagonal sensors require at least f/2.8 in order to function because they are high-precision sensors.

Important notes

Where "autofocus does not function" is noted, phase-detection autofocus is normally impossible, either when shooting through the viewfinder or with the Quick AF mode in Live View, but it is generally possible to autofocus using the contrast detection-based Live AF and Face Detection Live AF modes in Live View.

In addition, when an extender (teleconverter) is being used and the resulting aperture is less than what is normally required for AF, it may be possible to enable AF by taping the three extender-specific pins (which are opposite of the raised pins) on the lens side of the extender to prevent it from communicating extender information with the lens and camera, so that the camera sees the lens's aperture as though no extender is attached. This is not guaranteed to succeed as the AF system is not designed to operate under these conditions, and the Exif data will not reflect the use of the extender. Some third-party extenders may not communicate extender information with the lens and camera at all, with the same effect as the aforementioned "tape trick".

The limitations discussed hereafter generally do not apply to third-party zoom lenses that have maximum apertures of f/6.3 at the long end of the zoom range, as they actually report a maximum aperture of f/5.6 to the camera. Note, though, that faster third-party lenses should be able to autofocus as expected for their aperture, including any high-precision focusing capability normally supported by the lens and body.

All images in this answer should be attributed to Canon Inc.


Canon EOS Digital Rebel (original, 300D), Digital Rebel XT (350D), Rebel XS (1000D), Rebel T3 (1100D), D30, D60, 10D

All points function to f/5.6; the center point is normal-precision cross-type (it is both vertical- and horizontal-sensitive to f/5.6 and is not high precision at f/2.8). The other points are either horizontal or vertical sensitive only (not both) (EOS D30 and D60: vertical sensitive only). Autofocus does not function below f/5.6.

  • EOS D30 and D60: 3 AF points available.
  • EOS 10D, Digital Rebel (300D), Digital Rebel XT (350D), Rebel XS (1000D): 7 AF points available.
  • EOS Rebel T3 (1100D): 9 AF points available.

Canon EOS D30/D60 AF array
Canon EOS D30/D60 AF array

Canon EOS 1000D AF array
Canon EOS 1000D AF array

Note that the EOS Rebel T3 (1100D) has essentially the same AF point layout as those in the next group of cameras, only that the center point is not high precision at f/2.8.

Canon EOS Digital Rebel XTi (400D), Rebel XSi (450D), Rebel T1i (500D), Rebel T2i (550D), Rebel T3i (600D), Rebel SL1 (100D), Rebel T5 (1200D), 20D, 30D

The center point is high-precision only when the aperture is at least f/2.8. If below f/2.8 but at least f/5.6, all points function as either horizontal or vertical sensitive only, except for the center point, which functions as standard-precision cross-type. Autofocus does not function below f/5.6.

Canon EOS Rebel T3i (600D) AF array
Canon EOS Rebel T3i (600D) AF array

Canon EOS Rebel T4i (650D), Rebel T5i (700D), 40D, 50D, 60D

The center point is high-precision dual cross-type only when the aperture is at least f/2.8. If below f/2.8 but at least f/5.6, all points function as cross type, but the center point is single cross-type and normal precision only. Autofocus does not function below f/5.6. With the following lenses, the center point is normal-precision single cross-type, as if they were f/5.6 lenses:

  • EF 28-80mm f/2.8-4L USM
  • EF 50mm f/2.5 Compact Macro

With the following lenses, the outside points of the AF array are either horizontal or vertical sensitive (not both):

  • EF 35-80mm f/4-5.6 (all variants)
  • EF 35-105mm f/4-5.6 (original and original USM variants only)
  • EF 80-200mm f/4.5-5.6 (II and USM variants only)

(EOS Rebel T4i (650D): Though not included in the above link, this limitation is specified in the manual for this camera, page 99.)

Canon EOS 60D AF array
Canon EOS 60D AF array

Canon EOS 70D, 7D

The same aperture limits for the EOS Rebel T4i (650D), 40D, 50D, and 60D apply to the 7D, only that the 7D has 19 AF points instead of 9.

EOS 70D: The above applies to focusing when using the viewfinder. In Live View, with Dual Pixel CMOS AF, phase-detection autofocus with apertures as small as f/11 is possible across about 65% of the total frame area (80% height by 80% width). Dual Pixel CMOS AF is fully supported with more than 100 EF lenses, including all EF lenses currently in production. Other lenses will autofocus in a hybrid phase-detection/contrast-detection mode when in Live View.

Canon EOS 7D AF array
Canon EOS 7D AF array

Canon EOS 6D

The center point is high-precision cross-type only when the aperture is at least f/2.8; the other points are either horizontal or vertical sensitive (not both). If below f/2.8 but at least f/5.6, the center point remains cross-type but is normal precision only; all other points continue to function normally. Autofocus does not function below f/5.6.

Canon EOS 6D AF array
Canon EOS 6D AF array

Canon EOS 5D and EOS 5D Mark II

The center point is high-precision cross-type only when the aperture is at least f/2.8; the other points are either horizontal or vertical sensitive (not both). If below f/2.8 but at least f/5.6, the center point remains cross-type but is normal precision only; all other points continue to function normally. Two of the six invisible Assist AF points used in AI Servo AF are cross-type at f/2.8, with the rest horizontal sensitive; if below f/2.8 but at least f/5.6, they are all horizontal sensitive. Autofocus does not function below f/5.6.

Canon EOS 5D Mark II AF array
Canon EOS 5D Mark II AF array

Canon EOS-1D, EOS-1Ds, EOS-1D Mark II, EOS-1D Mark II N, EOS-1Ds Mark II

  • If at least f/2.8, all 45 autofocus points will function, with 7 points high-precision cross-type.
  • If at least f/4, all 45 autofocus points will function, but only the center point is high-precision cross-type.
  • If at least f/5.6, all 45 autofocus points will function as horizontal sensitive only.
  • If at least f/8, only the center point functions as horizontal sensitive only. The other points will not work.
  • Autofocus does not function below f/8.

Note that when using the EF 70-200mm f/2.8L USM lens (without IS) with an Extender, use the center point only as the other points may not focus correctly.

Canon EOS-1D Mark II AF array
Canon EOS-1D Mark II AF array

Canon EOS-1D Mark III, EOS-1Ds Mark III, EOS-1D Mark IV

  • If at least f/2.8, all 45 autofocus points will function, with 19 points high-precision cross-type. (EOS-1D Mark IV only, with manual point selection: 39 of the 45 points are high-precision cross-type.)

Canon EOS-1D Mark III AF array
Canon EOS-1D Mark III AF array

Canon EOS-1D Mark IV AF array
Canon EOS-1D Mark IV AF array

  • If at least f/4, all 45 autofocus points will function, but only the center point is high-precision cross-type.
  • If at least f/5.6, all 45 autofocus points will function as horizontal sensitive only.
  • If at least f/8, only the center point functions as horizontal sensitive only. The other points will not work.
  • Autofocus does not function below f/8.
  • There are exceptions:
    • All of the AF points will be horizontal sensitive only if a variable-aperture zoom lens is mounted, with the exception of the EF 28-80mm f/2.8-4L USM lens, which allows the center point to work as cross-type.
    • EOS-1D Mark III and EOS-1Ds Mark III: When using the EF 70-200mm f/2.8L USM lens (without IS) with an Extender, use the center point only as the other points may not focus correctly.
    • The following lenses do not allow the three points on the far left and far right to work as cross-type points (only horizontal sensitive) even though they have a maximum aperture of f/2.8:
      • EF 24mm f/2.8
      • EF 28mm f/2.8
    • EOS-1D Mark IV only: Some lenses and lens/extender combinations enable cross-type focusing with 39 of the 45 points, even though they have a maximum aperture of f/4:
      • EF 17-40mm f/4L USM
      • EF 24-105mm f/4L IS USM
      • EF 70-200mm f/2.8L IS USM with Extender EF 1.4X II
      • EF 200mm f/2L IS USM with Extender EF 2X II
      • EF 300mm f/2.8L IS USM with Extender EF 1.4X II
      • EF 400mm f/2.8L IS USM with Extender EF 1.4X II

Canon EOS 5D Mark III and EOS-1D X

Autofocus capabilities depend on which of the eight groups the lens in use falls into (see the Canon EOS-1D X AF Setting Guidebook, pages 36-39, and Canon EOS 5D Mark III manual, pages 79-84, for more details; a complete and easier-to-navigate list of lenses can be found here), as follows:

Canon EOS-1D X AF array
Canon EOS-1D X AF array

  • Group A: Most f/2.8 and faster lenses and lens/extender combinations, with the exception of those listed in Groups B, C, and D, support 41 cross-type points (21 in the center, f/5.6 sensitive, and 10 on each side, f/4 sensitive) and 5 dual cross-type points (in the center column, f/2.8 sensitive). The remaining points are horizontal-sensitive. All 61 AF points and AF area selection modes are available.

    Group A AF array: 61 points, 41 cross-type, 5 dual cross-type

  • Group B: These f/2.8 lenses allow the same functionality as Group A lenses except that only one point is f/2.8 dual cross-type:

    • EF 14mm f/2.8L USM
    • EF 14mm f/2.8L II USM
    • EF 15mm f/2.8 Fisheye
    • EF 20mm f/2.8 USM
    • EF 24mm f/2.8
    • EF 24mm f/2.8 IS USM
    • EF 28mm f/2.8 IS USM
    • EF 24-70mm f/2.8L USM (original variant only)

    Group B AF array: 61 points, 41 cross-type, 1 dual cross-type

  • Group C: Most f/4 lenses and lens/extender combinations support 41 cross-type points (none of the points are dual cross-type). All 61 AF points and AF area selection modes are available. A few macro lenses are in this group as well:

    • EF 50mm f/2.5 Compact Macro
    • EF 100mm f/2.8 Macro
    • EF 100mm f/2.8L Macro IS USM

    Group C AF array: 61 points, 41 cross-type

  • Group D: These f/2.8 lenses supports only 31 cross-type points (21 in the center, inner column of 5 on each side) and one f/2.8 dual cross-type point, although all 61 AF points and AF area selection modes are available.

    • EF 28mm f/2.8
    • EF 40mm f/2.8 STM (pancake lens introduced with EOS Rebel T4i)

    Group D AF array: 61 points, 31 cross-type, 1 dual cross-type

  • Group E: Most f/5.6 lens and lens/extender combinations support 21 cross-type points in the center (none of the side points are cross-type, and there are no dual cross-type points). All 61 AF points and AF area selection modes are available. A few macro lenses are in this group as well:

    • EF 50mm f/2.5 Compact Macro with Life-Size Converter EF
    • EF 100mm f/2.8 Macro USM

    Group E AF array: 61 points, 21 cross-type

  • Group F: These lenses support 21 cross-type points in the center, but a total of 47 points are available (seven points from the extremes at each side of the AF array are disabled), although all AF area selection modes are available:

    • EF 25-55mm f/4-5.6 USM
    • EF 28-70mm f/3.5-4.5 (all variants)
    • EF 28-80mm f/3.5-5.6 (all variants)
    • EF 28-105mm f/4-5.6 (original and original USM variants only)
    • EF 35-70mm f/3.5-4.5 (all variants)
    • EF 35-80mm f/4-5.6 (all variants)
    • EF 35-350mm f/3.5-5.6L USM
    • EF 80-200 f/4-5.6 (II and USM variants only)
    • EF 800mm f/5.6L IS USM

    Group F AF array: 47 points, 21 cross-type

  • Group G: These lenses and lens/extender combinations support 15 cross-type points in the center and a total of 33 points (the top and bottom three cross-type points in the center and 11 points from the extremes at each side of the AF array are disabled), although all AF area selection modes are available:

    • EF 180mm f/3.5L Macro USM
    • EF 180mm f/3.5L Macro USM with Extender EF 1.4x
    • EF 1200mm f/5.6L USM

    Group G AF array: 33 points, 15 cross-type

  • Group H: EOS-1D X with firmware version 1.1.1 or later, and EOS 5D Mark III with firmware version 1.2.1 or later (see this page): Most f/8 lens/extender combinations, the sole exception being EF 180mm f/3.5L Macro USM with Extender EF 2x (for which autofocus does not function), support autofocus with the center point only, which is cross-type (all other points are disabled). AF point expansion can be used (although only the center point can be selected), with four points adjacent to the center point acting as AF assist points. The points above and below the center point are vertical sensitive, while the points to the left and right of the center point are horizontal sensitive. Autofocus does not function below f/8. This group also includes the following lenses:

    • EF 35-105mm f/4.5-5.6
    • EF 35-105mm f/4.5-5.6 USM

    Group H AF array: One cross-type point, plus four AF assist points when AF point expansion is enabled

    EOS-1D X with firmware older than version 1.1.1 and EOS 5D Mark III with firmware older than version 1.2.1: Only the center point can be used (all other points are disabled) for the above EF 35-105mm lenses, and AF point expansion is not available. Autofocus does not function below f/5.6.

    Group H AF array with older firmware: One cross-type point

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This is all in the manuals, but it would be more convenient if there was a comprehensive list that can easily be found. I decided to "seed" this question and answer to help Canon users with regard to what their lenses allow in terms of autofocus. –  DragonLord Oct 15 '11 at 14:23
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@khedron, autofocus occurs with the lens wide open. If the maximum aperture is within the limits given in the answer, AF will work with the capabilities and limitations given above. The maximum aperture is indicated on the lens. For example, you may see "1:3.5-5.6" for f/3.5-5.6, so the maximum aperture varies with the zoom setting. The lens is stopped down only when you take a picture. –  DragonLord Nov 7 '11 at 17:54
1  
What about lenses that aren't manufactured by Canon? Does e.g. Tamron 17-50mm f/2.8 enable use of center high-precision point in xxxD/Rebels? –  Baczek Oct 17 '12 at 17:48
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@Baczek: Yes, you should be able to get high-precision AF with this lens, as it reports f/2.8 to the camera. –  DragonLord Oct 17 '12 at 19:38
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@ides: Yes. This condition typically only arises when an extender is used. Note that the relevant aperture value is the maximum aperture. Even if your lens stops down to f/11, f/16, etc., what matters is the smallest f/number (largest aperture) the lens supports. –  DragonLord Jul 5 '13 at 2:19
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A recent discovery -- the Kenko teleconverters allow for autofocus at F/8 on most (if not all) Canon bodies. See for instance Art Morris: http://www.birdsasart-blog.com/2012/08/30/mega-amazing-discovery-800-f5-6-1-4x-tc-canon-eos-1dx/

I've started experimenting with the combination of a Kenko 2.0x teleconvert and a Canon 300 F/4 lens, which gives me a 600mm/F8. My initial experiments show that this combination on a 7D does, in fact, enable autofocus.

It should be noted that the combination needs good light; it doesn't seem to work well in poor light. It's slow. It's not always consistent. but it works.

it's too early for me to decide whether or not this is a combo I'd trust in field conditions on a regular basis (my initial take on the image quality is that they're sharp enough but I find the images a bit overexposed and the contrast is weak. Both are fixable either by adjustments on the camera or in post, but are definitely going to need to be evaluated further).

It does, however, work, and give me a 600mm lens for < $1400 if bought new. And it works well enough to at least be work experimenting with. The Kenko 1.4x might be an interesting expriment on some of the F5.6 lenses as Morris notes, too.

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Answer updated to account for this. –  DragonLord Jan 1 '13 at 20:44
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Just wanted to point that the information about focus points in EOS 600D/550D/500D/450D might not be accurate.

" Canon EOS Digital Rebel XTi (400D), Rebel XSi (450D), Rebel T1i (500D), Rebel T2i (550D), Rebel T3i (600D), 30D

The center point is high-precision cross-type only when the aperture is at least f/2.8. If below f/2.8 but at least f/5.6, all points function as either horizontal or vertical sensitive only (not both). Below f/5.6, autofocus does not function. "

Canon website : "AF System/ Points 9 AF points (f/5.6 cross type at centre, extra sensitivity at f/2.8) "

Same is with 6D AF center point (f/5.6 cross type at centre, extra sensitivity at f/2.8), witch is same as in this article.

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