topic Re: R5Mk2 : Detect priority AE while AF in EOS DSLR & Mirrorless Cameras

EOS R5 Mark II : Detect priority AE while AF

thegios — Sun, 21 Sep 2025 17:07:24 GMT

IMPORTANT: all I will be saying applies to EVALUATIVE MODE only.

FACT 1: Canon says that evaluative mode is a general-purpose metering mode suited even for backlit subjects, doesn't really say if there's a bias towards point(s) in focus, although many photographers say it does. By experience I can indeed say it does: if I put a person or a chair against a bright background, focusing on the perosn/chair gives me a quite difefrent exposure than focusing on the background. This is also prooved by the fact that Canon also says that when AE Lock is engaged the exposure centered on the AF point in focus is locked.

FACT 2: There is difference between POINT(S)/AREA in focus (from now on POINT in focus, for simplicitly) and SUBJECT in focus. As confirmed to me by a Canon product owner, If you have subject detection on but there's no detected subject and camera focuses on a chair, the chair is not a subject. This is important to understand how "Detect priority AE while AF" works (see next). Said otherwise, if subject detection is on and we have something in focus and this something is detected to be a persion/aniaml/vehicle, then we have a subject in focus, any other "something" in focus is not a subject in focus. This also means that a SUBJECT in focus is a special case of POINT in focus. This laso means that if subject detection is off, whatever is in focus is just a POINT in focus, even a person/vehicle/anial in focus is not a SUBJECT in focus but simply a POINT in focus: a person /vehicle/animal is a SUBJECT in focus if and only if subject detection is on and that person/vehicle/animal is in focus.

If we all agree on the above two facts, let's talk about the new option that Canon has introduces for R5Mk2: "Detect priority AE while AF", also known as "AE for Priority Subjects During AF". Canon says that in evaluative mode if "Detect priority AE while AF" is on and subject detection is on then metering is based on the AF point(s)/area where the subject was detected: said otherwise, if "Detect priority AE while AF" is on and subject detection is on and there is a SUBJECT in focus then metering is based on this SUBJECT in focus.

BUT... if we agree that in evaluative mode the exposure is already biased towards the POINT in focus, and a SUBJECT in focus is a special case of a POINT in focus, why do we need then this new "Detect priority AE while AF" option?

I am asking because I honestly do not understanbd at this point the difference between

A. Evaluative + "Detect priority AE while AF" OFF + "Subject Detection" OFF or ON + a chair or a person in focus against a bright white backgroud

> I expect the camera to consider the whole scene with a bias on the chair or the person that are considered a either a POINT or a SUBJECT IN FOCUS (depending if subject detection is off or on) but in any case "Detect priority AE while AF" is off.

B. Evaluative + "Detect priority AE while AF" ON + "Subject Detection" OFF + a chair or a person in focus against a bright white backgroud

> I expect the camera to consider the whole scene with a bias on the chair or the person that are considered a POINT IN FOCUS, being subject detection off (even if "Detect priority AE while AF" is on).

C. Evaluative + "Detect priority AE while AF" ON + "Subject Detection" ON+ a chair in focus against a bright white backgroud

> I expect the camera to consider the whole scene with a bias on the chair that is considered a POINT IN FOCUS (even if subject detection is on a chair is not a SUBJECT not being a person/vehicle/animal).

D. Evaluative + "Detect priority AE while AF" ON + "Subject Detection" ON + a person in focus against a bright white backgroud

> I expect the camera to consider the whole scene with a bias on the person that is considered a SUBJECT IN FOCUS

Re: R5Mk2 : Detect priority AE while AF

thegios — Thu, 31 Oct 2024 06:47:07 GMT

Any Canon expert here who could shade some lights?

Re: R5Mk2 : Detect priority AE while AF

Hazel_T — Fri, 01 Nov 2024 22:32:46 GMT

Hi thegios,

The main difference is that the main metering modes are completely unrelated to your focusing method. The main metering modes are based on different portions of the sensor concentrating down to the center of the frame. Evaluative metering using the entire frame to meter the light and the smallest metering mode Spot metering is about the center 10% of the frame. The portion of the frame the camera is using to meter in those modes doesn't adjust depending on where your focus point is set. So if you have the camera set to Spot metering it always uses the center point to meter even if your auto focus point is to the side of the frame.

So the reason evaluative metering can be helpful with backlit shots is because it is using the light levels of everything in the frame to find a middle ground. That way you can get a more even exposure for the under lit and brighter areas.

Detect Priority AE while AF was added so that you can select a subject to track and the camera will only meter based off of the active auto focus points. That way it is adjusting as your subject is moving around the frame. It is the only metering type that is tied to focus points. The Detect Priority AE while AF metering method does not stack with other metering types (like Evaluative, Center Weighted, Partial, or Spot metering). When Detect Priority AE while AF is enabled the camera is only metering based on the active AF points.

If you would like to reference the manual for information on the metering modes it is on pages 330-332. If you need a copy of the current manual it is available HERE. Once you are on the web page click on the Manuals button and the one to reference is named EOS R5 Mark II Advanced User Guide.

Re: R5Mk2 : Detect priority AE while AF

thegios — Sat, 02 Nov 2024 08:18:11 GMT

"Detect Priority AE while AF was added so that you can select a subject to track and the camera will only meter based off of the active auto focus points... It is the only metering type that is tied to focus points... When Detect Priority AE while AF is enabled the camera is only metering based on the active AF points."

So is it correct to say that if I am in evaluative and I am tracking a person walking against a very bright background:

- if Detect Priority AE while AF is off, metering considers the whole scene with a bias on the person in focus

- if Detect Priority AE while AF is on, metering considers only the person in focus

Re: R5Mk2 : Detect priority AE while AF

Waddizzle — Sat, 02 Nov 2024 18:51:18 GMT

This is a very good explanation. But you’re overlooking one basic difference between your Point and Subject. Tracking.

The camera is able to track Subjects, but not Points. I think this is the piece of the puzzle that you’re looking for.

Re: R5Mk2 : Detect priority AE while AF

thegios — Sat, 02 Nov 2024 19:00:59 GMT

Actually it is clear to me, yet tracking is not involved here.

Re: R5Mk2 : Detect priority AE while AF

nelu — Tue, 16 Sep 2025 19:31:22 GMT

Hello,

Good explanation of what the camera is supposed to do, except it doesn't do it.

Today's example, with Canon EOS R1 though, not R5 Mark II, but this feature should work the same.

Scenario:

Subject: people, walking from left to right of the frame.
Light: strongly backlit on the left of the frame, in the shade on the right of the frame
Metering mode: Evaluative
Camera on manual (AutoISO, fixed time and aperture)
Detect: people
Achieved results: Left of the frame (backlit): very dark faces or body shapes. Right side of the frame (in the shade): properly exposed
Measured ISO's, frames from left to right: 500,500,500,500,800,1250,1600, 2000,2000

Apply this to birds in flight and you'll get black silhouettes. Try to lift the exposure for shadows and you get horrible noise even at ISO 400.

Re: R5Mk2 : Detect priority AE while AF

thegios — Thu, 18 Sep 2025 13:38:43 GMT

I'll check results from my 2 days in Jakarta where I've been shooting on the streets in evaluative and this option on, most of the time in Av with auto ISO.

But I see what I mean... I believe Canon has over-complicated a few things with R34/R5Mk2. They should have used the same approach as for the R1: either the normal evaluative we're used to (whole scene with a bias non point kn focus) or the possibility to link exposure to point in focus.