Our reader Jim sent me this text:
For the latest Olympus Flash (the FL-700WR with radio control), the multi-language user’s manual can be download from:
I have studied the documentation concerning various flashes by Olympus and published two articles (in French) on:
The flash power, given as a Guide Number at 100 ISO, corresponds for Olympus to the longest corresponding zoom focal length covered, which is the most favourable (highest number).
This makes it difficult to compare different flashes that have different focal ranges.
The data for all flashes are from the Olympus documentation, except for my FL-900R where I found no data from Olympus but was able to read all the figures on the back panel with the flash set to manual and varying the focal length.
The table and graph attached here are an attempt to clarify matters: they give the Guide Numbers in metres of focal length v/s zoom length in mm of true Olympus focal length.
Hoping that helps.