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When the lens has a serial number "1234567890" engraved, the encoding sheme is simple binary coded decimal (BCD):

Code Select Expand


DCL 0x85 0x00 0x00 0x00 0x00 0x00
DLC ...  0x12 0x34 0x56 0x78 0x90

Out of the lenses I tested, only a few transmit the serial number. I think currently only the professinal line of lenses with the red "L" marking released in recent years transmit the serial number. I can confirm 0x85 working on the Canon EF 24-105mm f/4 L IS II USM.

You can test it by connecting the lens to a recent camera body, like a EOS 5DmIV. If the serial number is shown in the sub-menu for the AF microadjustment, then this command should work. It then will also write the serial number correctly to the EXIF information in the JPEGs.

You are correct that that the EF 50mm/1:1.4 (too old) and EF 50mm/1:1.8 STM (too cheap) do not transmit the serial number.

@JP79dsfr:
The lens serial number for Canon EF-lenses is transmitted with the 0x85 command.

Is there a way to intercept the raw data that is sent or received over the electrical connection pins in the EF-Mount from within ML ?
Are there any adressess that are constantly changing while there is communication going on with lens?

Btw.: the probably currently best compilation of the Canon EOS EF-mount protocol can be found in this post: www.dslr-forum.de/showpost.php?p=12221153&postcount=554