|Click on photo to see it larger|
By just changing your ISO when using your flash you can change the look of the background. With the camera on a tripod and using Aperture priority mode all I did between these three photos was change the ISO from ISO 100 [far left], ISO 400 [center] and ISO 2000 [far right].
I have the flash off camera to the left as you see in the diagram below. The flash setting is normal mode. The flash is in TTL model so that it is adjusting as needed to the scene.
|Click on the photo to see it larger|
As the ISO goes higher the odds of you blowing out the subject with the flash will go up. As you lower the ISO the darker the background.
As you change the ISO the only other setting changing since I am in Aperture mode is shutter speed. Now unless you want a blurred image you need to keep that shutter speed close to the focal length of the lens. If you have a 35mm lens then try to shoot at 1/30 or faster. If you are shooting with a 200mm lens then you need to be at 1/200 or 1/250.
For these photos I have the flash on the camera with white dome and bounced. The reason the photos are so similar is the shutter speed adjusts to make the background match the foreground subject.
If these were not on a tripod you would see much more blur with the first on shot at 1/6 shutter speed.
|ISO 100, ƒ/1.8, 1/6|
|ISO 400, ƒ/1.8, 1/25|
|ISO 6400, ƒ/1.8, 1/500|
Are you controlling your camera or is it controlling you? The more you understand how the camera works the more creative you can be and decide yourself what the look will be in the final product.