What does the ISO setting on the actual flash gun do?

[ajax_andy]

So on my Nissin di866 mark ii flash I can change 3 things:

Power - obvious what this does
Zoom - spread of light
ISO

No idea what the ISO option on the flash is for... it's set to 250 as standard so have always left it on this, but would like to understand why it's there and if I change it what it'll do?

 

[JonathanRyan]

Does it have a distance readout? It will affect the calculation for that.

Also if it has an automatic mode it will use it for that.

 

[Keltica]

For the basics then set your ISO on the flash to that of the camera but I just had a look and it's got TTL and I assume it syncs with the camera when it's connected through the hotshoe, so no need to set the ISO on the flash, as I'm assuming that the flash and the camera will talk to each other (not a proper conversation you understand)..

 

[gary996]

This is what it says in the manual:
As for the non-dedicated or traditional type film
cameras, the film speed (ISO) information is not
transferred from the camera.
In this case, the film speed (ISO) is to be set on the
flash unit to indicate the camera-subject distance.

 

[ajax_andy]

This is what it says in the manual:
As for the non-dedicated or traditional type film
cameras, the film speed (ISO) information is not
transferred from the camera.
In this case, the film speed (ISO) is to be set on the
flash unit to indicate the camera-subject distance.

That's quite interesting as my flash always says it's set to 22m regardless of the ISO set... any idea why that might be?