How are FocusDistanceUpper and FocusDistanceLower Calculated?

[dannarsh]

Hi All,

I've searched through the forums here (and elsewhere) to try and find a clear answer to this.
I am using a Canon EOS D60 with EF 28mm - 135mm lens. Originally I wanted to use the meta data to collect the focus distance but it looks like that isn't a likely pursuit...

What I'm curious about is if anyone knows where the "FocusDistanceUpper" and "FocusDistanceLower" values come from or how they are calculated? I have seen this post (https://exiftool.org/forum/index.php/topic,3765.msg17267.html#msg17267) where BogdanH performed the test of adjusting the focus ring slightly and collecting the values. But is it clear to anyone where those values come from? Two chats with Canon tech support have not provided an answer, they hint that it might be created 3rd party.

My best guess is the lens has a sensor for the focus ring, and just equates a sensor reading to a look up table in the camera body?

Any help is appreciated and thank you for your time!

Best,

Dan

[Phil Harvey]

Hi Dan,

That would be my guess, but I don't know for sure.

- Phil