When you do a studio portrait, you usually want to use your portrait lighting alone – the room light should not interfere. Room light should be invisible.

Does this mean the room has to be dark?

No. It just means  the room has to look dark to the camera.

So for a studio shot, first do a test. Disable the flash, and set your camera to:

• Manual exposure mode
• 100 ISO (or 200 ISO if 100 is impossible on your camera)
• f/8
• 1/125th second

Fire off a test shot:

Bingo. Now the flash will light your subject – and only the flash.

Was that room dark? No. To you or me (or to a caerma with different settings) the room looked like this: quite bright, what with the room lights and the flashes’ modeling lights!