EXiF Question

I notice that when I check out the EXiF on some photos, buried in the lens data, I see 'Approximate Focus Distance'. However, on my own photos, I don't see this. Is that data a lens function, camera function, or software function? How can I pull that info?

I have a 50D, an assortment of lenses (Canon, Sigma, Tamron), DPP, LR5.3, PS6.

Lens function.

The lens has to report the focus distance to the camera. Of course the lens knows nothing about distances out there in the big world, all it knows is focusing barrel position - how much it turned before the AF told it to stop or how much it was rotated manually. This means it must have sensors to detect barrel position and a firmware chip to translate that into feet or meters. It is an "added value" addition that goes into only the more expensive lenses.

Thanks!

I believe that Canon use this distance information from the lens, where it is present, to bias the flash output when shooting with ETTL II flash.

Alan

BigAl007 wrote in post #16533707
I believe that Canon use this distance information from the lens, where it is present, to bias the flash output when shooting with ETTL II flash.

Alan

True, and in addition, because ETTL II changes the power of the flash to achieve proper exposure and changing power changes the color of the light, it automatically changes the WB if it is set to AWB or Flash.

BigAl007 wrote in post #16533707
I believe that Canon use this distance information from the lens, where it is present, to bias the flash output when shooting with ETTL II flash.

Alan

Interesting you mention this... I was reading this thread last night, which was discussing the use of (or lack of) the distance information with ETTL.

Note that focus distance is available in the EXIF.

OK, my in-depth Exif stuff is buried somewhere, do you get this "distance" stuff without a flash???

It's also about as accurate as throwing a dart at a target 40ft away; so I wouldn't factor it into anything I cared about.

tonylong wrote in post #16535604
OK, my in-depth Exif stuff is buried somewhere, do you get this "distance" stuff without a flash???

"Buried" is the correct word. In ExifToolGUI I found it in the Maker Notes section, not the Exif, and it is given as a range, like 3.61 - 4.16 m. In PSE 12's File Info which is a very extensive collection of file metadata and xmp data it is in the Raw Data tab (the last of 14) and there, for the same photo, it is reported as approximately 3.82. Various other programs show only "Exif highlights", an incomplete version of the Exif section of the metadata.

I'm reviving this thread, as now I question what has been said above.

It's said to be a function of the lens (approx. focal distance), but as I was going through the thread on the new Tamron 150-600mm, I noticed that in images where the exif wasn't stripped, and appears to be fully in tact, some bodies are showing that data, and some are not all the time. I'm very confused.

I don't take the distance as precise, but it helps me in learning how far away some of the birders are for their shots.

First the lens has to report the distance to the camera and then (second) the camera has to write it into the metadata. All do so, but not in a place that all editing applications read. So it depends on what the editor reads and then (third factor) writes into its truncated version of the Exif when it saves the jpg.