Feature request: Canon AF precision type

[Kamae]

Hello,

is it possible to extract the AF precision type from the Canon RAW file? For example, on the 70D the middle AF point has a separate operation mode for lenses with apertures wider or equal than 2.8, a high precision mode. I don't know any program nor an in-camera possibility to show me, whether the camera used high-precision mode or not when taking a picture with the center AF point on my 70D.

There are ongoing discussions about problems of some 70Ds with fast lenses having focus issues at longer distances. Choosing an outer-center AF point solves this problem on these affected models as well as using the center AF point with slower lenses, where the camera has to use the "normal" precision mode.

I know that it is not very likely, but it could be that every 70D is affected and that users like me (who don't have AF issues at all, at least not knowing it) just have a stronger defect with the high precision mode, that the camera does not find a focus in high-precision mode at all, thus doing a fallback to normal precision which works fine with every affected camera.

From the outside - without a possibility to see which precision mode was used - it's just a black box. Or maybe you know another possibility to determine which precision mode the camera has been used?

Regards
Andre

[Hayo Baan]

Does Canon's own software (eg. DPP) show you this information? If so, then there may be a chance that other software (best chance would then be Phil Harvey's exiftool) can determine it too. But to be honest, I don't think this piece of information is stored in the file at all

[Phil Harvey]

Hi Andre,

Looking at a sample 70D image, most of the AF information seems to be decoded.  My guess is that Hayo is correct and the information you want just isn't stored.  But if it was there, the only way to find it would be to have a number of samples for which this state is known.  (I am assuming that the Canon software doesn't display this.)

- Phil

[Kamae]

Hi Hayo and Phil,

thank you very much for your answers. I haven't seen the information in Canon's own software DPP; either I looked at the wrong places or it's just not shown. But knowing which kind of - sometimes useless - information Canon records in their RAW files, it's hard for me believing that they don't include this AF information which would enable them to track down AF problems during development phase of a new camera model as well as customer support requests.

Supplying sample images where the state is known is the main problem. It's for sure, that the camera can't use high precision mode for slow lenses (let's say open aperture f/4 or worse). But that's only one side of the medal. For fast lenses, the state would be unknown, that's why I wanted the information to be shown in the ExifTool.

And I really don't know how one could estimate whether high precision has been used or not. I don't even know the consequences. To simplify the conceptual model, let x be a value between 0 (narrow) and 100 (far away) to control the focus on the lens. Then I would expect, that the normal precision mode (center focus point with slow lenses and all other focus points) would deliver not every possible value, for example: 0, 5, 10, 15, ..., 95, 100, and high precision mode would deliver every possible value: 0, 1, 2, 3, ..., 99, 100. So that for fast lenses where the depth of field is very narrow there would be finer steps for controlling the lens' focus.
But I don't know a possibility for checking and making a conclusion whether high-precision mode is active or not when taking a picture (I don't see how "wide" the focus steps determined by the AF are).

Thinking about that: Phil, did you notice "missing" AF values in the AF information of Canon cameras with slow lenses compared to the whole range of possible AF values? Maybe an implicit conclusion would be possible if some AF values don't occur on slow lenses but only on fast lenses. In the example above, getting the value 4 would implicitly mean that high-precision mode has been used. Ok, value 5 could be in both modes. But maybe the clear cases would be sufficient to build up a sample image base (pictures with slow lenses using center AF point for the negative case, pictures with AF values only possible with high precision mode) to find the explicit attribute inside Canon's AF information inside the RAW file.

[Phil Harvey]

Hi Andre,

Phil, did you notice "missing" AF values in the AF information of Canon cameras with slow lenses compared to the whole range of possible AF values?

I don't have a large enough sample of 70D images to make any observations like this.

- Phil