Flashgun Question

[petrolveins]

Another question for all you decent photographers who are forever pestered by us morons .

I've been happily playing away with my two jessops flashguns and the poverty wizards I have for them, using trial and error in order to get the aperture correct on the camera. Now that I've sort of got to grips with that and choosing the power and zoom, I noticed that sometimes my flash guns give me the option of choosing both the iso and f/stop for the flash.

Now this may be a really stupid question, but should the f/stop and iso be set to the same as the camera or does it affect the flash output in some way? What does it actually do in terms of the light produced? It's odd because despite using the manual flash mode all the time, it only sometimes asks for this. I did resort to reading the manual which didn't help, and so far nor has google.

Can anyone help me out here?

[Simpo Two]

Flashguns don't have an ISO or an aperture - all they do is emit light, to a greater or lesser extent, and sometimes with a varying beam width.

What I think the settings are doing is changing the flash output according to what you set on the camera. In other words, if you change the camera from ISO 100 to ISO 200, you tell this to the flashgun so it knows to give half as much light. The flashgun has to be told manually by you because it can't 'talk' to the camera to find out for itself what's going on at the business end.