Help with the 420 EX in non-TTL use
The 420EX always works in E-TTL.
In order to always work in E-TTL, it always has a preflash.
And I do not know how you set the preflash off BEFORE the shutter opens, and then set the "real" flash off WHEN the shutter opens.
If you had a 430EX, which has a manual switch, you could probably use it.
420EX also works in traditional TTL without pre-flash on older EOS models. Mounted on non-EOS, it won't receive the communication it expects for E-TTL or TTL and will probably (I could be wrong) simply fire a single flash at full output at shutter open.
IMHO-- hide signature --
Unapologetic Canon Apologist
Thanks for responding. The flash does fire, and I think you are correct, at full power. If that is the case, I assume the GN is 138.