So, here's my rule for picking ISO in the studio: THE F-STOP YOU REQUIRE FROM YOUR WEAKEST LIGHT DETERMINES YOUR ISO IN THE STUDIO--PERIOD.
In my studio the ceiling mounted "hair-light", which shares my Norman pack, with two other heads that are lighting my background, is my weakest light. To get f11.0 from that light at full power requires ISO 200. It's that simple; my starting studio ISO is 200.
As an example of creative use of ISO in the studio I decided to do something different with an image of one of my older cameras I had up for sale. I placed the camera in front of one of the art prints that had been done with that camera. I loved the wild red sunset as the camera's background.
|f22.0 @ 1/5th second ISO 800 - Lens at 82mm
The basic rule here is that the shutter speed exposes for the continuous light (the flashlight) and the f-stop exposes for the flash; simple. Anyway, I did sell the camera! And I ended up with this nice image to illustrate high ISO and mixed lighting in the studio.
As always, should you have questions please don't hesitate to drop me a note.
Author: Jerry W. Venz, Master Photographer, Certified
Training site web address: http://www.LightAtTheEdge.com