Flash: Which ISO-setting ?

[CGNKlaus]

Which setting do you use when you take pictures with flash ? Do you leave it to 100 ISO or do you change it to f.e. 400 ?

[RichardtheSane]

What ISO I use for flash depends on what I am shooting, the lighting conditions and what I wish to achieve with the shot.

WHen there is plenty of light and I am doing fill flash only I use ISO 100, but if there is less light and I wasn the same result I up the ISO.

If I want the background darker I lower the ISO.

SO I don;t use one setting, I change it as the shot requires.

[scottbergerphoto]

Just to add to Richard:
The ISO controls the available shutter speeds and the noise level. Use the Lowest ISO to acheive the results you want. This comes into play when you need more distance from your flash, or trying to capture ambient light and still be able to hand hold the camera.
A handy formula:
Flash Distance = Guide Number / F stop at ISO 100
For ISO 200 multiply by 1.4
For ISO 400 multiply by 2

Scott

[tomasil]

Just to add to Richard:
The ISO controls the available shutter speeds and the noise level. Use the Lowest ISO to acheive the results you want. This comes into play when you need more distance from your flash, or trying to capture ambient light and still be able to hand hold the camera.
A handy formula:
Flash Distance = Guide Number / F stop at ISO 100
For ISO 200 multiply by 1.4
For ISO 400 multiply by 2

Scott

Hi,
Not sure I'm understanding this thread. The flashes I use (420EX, 550EX) are auto-exposure in that they adjust to the camera's settings, etc., which are or may be auto-exposure. Could you be implying a situation in which the camera is in Manual mode?
Please explain. :o
Thanks,
Tony

[rodbunn]

It's been my experience that the photos look more
natural with the flash at Iso's greater than 100. More like
400 looks better to me.... JMHO.

Later, Rod

[scottbergerphoto]

Just to add to Richard:
The ISO controls the available shutter speeds and the noise level. Use the Lowest ISO to acheive the results you want. This comes into play when you need more distance from your flash, or trying to capture ambient light and still be able to hand hold the camera.
A handy formula:
Flash Distance = Guide Number / F stop at ISO 100
For ISO 200 multiply by 1.4
For ISO 400 multiply by 2

Scott

Hi,
Not sure I'm understanding this thread. The flashes I use (420EX, 550EX) are auto-exposure in that they adjust to the camera's settings, etc., which are or may be auto-exposure. Could you be implying a situation in which the camera is in Manual mode?
Please explain. :o
Thanks,
Tony
1. If you are in ISO 100, a 550EX in ETTL can travel a maximum of 55 Meters and still properly expose a subject at f/1.0. If your subject is farther away, you need to increase your ISO for the flash to be able to do its job.

2. You are using flash to capture a picture and want to capture some ambient light so the background doesn't go black. At ISO 100 you find that the shutter speed for the ambient exposure is 1/30 sec. This is to slow to hand hold. You'll get a blurry shot, particularly the background. If you increase the ISO to 200, you can increase your shutter speed to 1/60. (Note: In P mode, the camera won't go below 1/60 by design in flash mode. You need to check the required shutter speed for the ambient light by going into M mode orAv to see if the ambient light will be recorded at the shutter speed selected by P mode. In other words if the required shutter speed is 1/30 the background will be dark in P mode due to its 1/60 floor unless you raise the ISO.)

In neither of these situations is the camera in Manual Mode. You are just changing the ISO and letting the camera and flash do the rest.
Scott