What's the best way to use a flash and colour gel as a back light?

Question

I want to know what is the best way of setting up a background flash with a coloured gel in a studio setting.

I had a play around with this on Saturday. I started with a white background infinity cove setup using four studio flashes. I turned off the two that were on the background and put a speedlight in front of the background with a blue colour gel. It was pointing at a slight angle from right to left.

The idea was to light the background with a gradient blue effect. I did succeed but only by modifying the saturation on the blue in post processing because originally it was not bright enough. The flash was set to high power but I only had a faint blue colour come through in the originals.

I want to know what is the best settings to use for this so I can get a nice blue background without having to edit them pictures so much.

Answer 1

My guess is that the studio lights overpowered the speedlight to the point it was barely contributing to the lighting.

Next time turn off all the studio lights, place the speedlight with the gel, take test photos and adjust the camera settings until you get the effect you want (or maybe just a bit darker then you want), then turn on the studio lights and adjust the power down until you get good exposure on the subject without changing camera settings.

Also:

1. Place the speedlight as close to the background as possible (this will both increase the light power and make the gradient more pronounced).

2. Place the subject as far from the background as possible and the studio lights close to the subject (this will reduce the amount of lights from the studio strobes hitting the background)