ISO help

[Cartman2000]

hi i need some help.. when shooting outdoors at night in a city area with flash, what range of ISOs should I be looking at? Normally i shoot at 200 in daylight, 400-800 in slightly darker settings and >1000 for night without flash.

another thing, when shooting those dark conditions of a ballroom dinner with flash, will 1600 be enough or do i have to go for the max 3200? i have heard that i should shoot at manual mode as well. thanks, appreciate the input.

 

[Octarine]

A lot depends on your camera and how much noise you can tolerate / remove with your software. To avoid noise you should use lowest possible ISO. Increase ISO only when necessary in order to get faster shutter speed. That means: stationary objects at night don't need any high ISO, they need a tripod.
For flash it's the same: adjust the ISO to get enough ambient light, then fill the rest with flash (that's why it's called "Fill Flash"). Also here: get a shutter speed that is fast enough to freeze motion. Stationary objects don't need fast shutter, ballroom will need it. Use Av to define DOF, then adjust ISO to get a shutter speed of at least 1/60. You don't need the background to be exposed properly, it's safe to leave it at EV-2 by increasing the shutter speed further. Fill in for the foreground and you'll get good results.
In addition you need to check your metering. Spot or centre weighted is more helpful for ballroom.

 

[Cartman2000]

ok thanks for the input. however im wondering if its wise to use 2 flashes, ceiling bounce.

i plan on shooting at f2.8 for the night for group photos, and about 4.0 should the stage performers start moving about

 

[Octarine]

ok thanks for the input. however im wondering if its wise to use 2 flashes, ceiling bounce.

That depends on your intended outcome. Using diffuser can be enough. 2 flashes will create also 2 shadows ...

i plan on shooting at f2.8 for the night for group photos, and about 4.0 should the stage performers start moving about

f/2.8 might not be good, the resulting DOF could be too shallow. Check this site and calculate the resulting DOF according your setup: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
Keep in mind: the output of the flash defines the exposure in such situations, aperture and ISO define how much is captured, shutter speed is less relevant.