Thanks for this information. It is unfortunate that Sigma reuses the same lens ID's, but of course they are constrained to work within the space that Canon has provided them.
When this happens, I am tempted to drop the details about the Sigma lenses to shorten the string. So how about something like this?:
"Canon EF 180mm Macro f/3.5L or Sigma 180mm F3.5 or 150mm f/2.8 Macro"
- Phil
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