Extension tubes questions

When extension tubes have contacts to keep AF and shot-snap aperture alive, which ones have just electric passthrough and which ones actually change the EXIF data to note the presence of the tube? Maybe even enter the corrected focal length?

Do Canon's own do that? The extenders do it, but the tubes?

My understanding is that the extension tubes do not change the focal length, they just extend the focusing range (i.e put the lens out further for more close range focusing).

I have the Canon tubes. They do keep AF and aperture control however there is no change to the EXIF when using them.

I have Kenko AF tubes. Maintains AF, metering, and Ap control. I've never checked the EXIF data, but I imagine it registers as the same FL as normal.
Tubes sort of "magnify" the image projected onto the sensor and decrease the minimum focusing distance.

i don't think there are any tubes that will report in the exif...would be kind of cool, but it's one of those times when you have to rely on your memory...

Thanks, guys. So the electronics are just wires, no signal modifications.

Any specific recommendation as to which product?

Reviewing reviews it seems that are some concerns that the cheap ones might damage lens mounts or contacts. Wouldn't want that to happen to the 85L now would I?

uOpt :You can't go wrong with the Kenkos. A decent price, for a quality-made 3 tube set.. more expensive than other off- brands, but cheaper than Canon's own.

Kenko Tubes