We actually measured the focal distance of the wide conversion lens on ZV-1 and found that you can photograph with the focal length of 18mm. However, changing the aspect ratio or setting the hand-shake correction function ON on ZV-1 will change the focal length.
Regarding other cameras, the focal length will differ according to its sensor size and lens configuration. Also, the focal length will change depending on the step-up and step-down ring used.
Please understand that the focal distance shown in the specification is an approximate amount.