Until now, my discussions have been confined to just using one flash.

As you progress in your technical abilities, you will find you might like having a 2nd flash.

When you use a low shutter speed, you are actually using 3 lights sources: the 2 flash units and the ambient or available light. If you are working at night, you  have 2.

Cross lighting

Placing one light on the left and right of your subject by itself doesn’t make your subject stand out.

It’s the ratio of the 2 lights and the ambient light that creates the depth.

Apart from the motion blur, either because of camera shake  or a moving subject, there can be one other side effect:

Mismatch in White Balance or color temperature.

In the days of transparency film, photographers used to carry all manner of filters to correct for the differences in color temperature.

The more meticulous ones actually carried a color meter.

These days, with that LCD on the back, you can “chimp” to almost see what the color, exposure looks like.

If you look at these 2 pictures, you’ll see a mismatch in the color.

Where the flash lit the subject, skin tones look great but in the background where ambient light was allowed to be recorded because I lowered the shutter speed, the scene looks yellow.

My camera was set for the color temperature of flash or daylight but the tungsten light bulbs made things yellow.

The diagram on the left shows the placement of my lights.

Cross lighting is fairly simple to do.

If both lights are giving you the same output, you just have to  place one light half the distance closer than the other.

Then base you exposure on the light that is closer to the subject since it’s the Main or Key light.

The other light which is twice as far will be the Fill light.

A final note about cross lighting. Watch that the light from your flash doesn’t cause flare and mar your image.

If you need to, use a lens hood. If that doesn’t help then place something between you and that light, like your hand.