Gary Fong colored gels, used with Whale Tail?

I have a Gary Fong Whale Tail and so far I've really been satisfied with the results it's given - I decided to purchase another one to test out using the colored gels to change the color of a simple white backdrop -

I watched the video that came with the gels regarding creating that effect but it didn't work for me - my background stayed white, no color cast.



I used two sb800 speedlights on stands - one with the whaletale w/ colored gel pretty close to the back drop, camera left - and the other camera right back of the room with a shoot thru umbrella.



My room is small, 12X10 I think so I'm thinking that maybe the left light was overpowering the one with the colored gel? I tinkered with the settings on both lights, lowering the power and so forth, still no luck. Not really sure what I'm doing wrong - anyone have any experience with this product that can %26quot;shed some light%26quot; to me on how to create this effect? I would so appreciate it!Gary Fong colored gels, used with Whale Tail?
This is a pretty typical studio lighting problem.



First I suggest you turn off your main light and get your backdrop exposure right - they should show you the gel filter effect. A flash meter will be useful at this stage.



Once you have that exposure right you need to sort out the fall off on your main light... To do this you need to have the subject close to the light source. The closer the light source to the subject the more rapidly the lighting will fall off as it heads towards the backdrop. (This applies the 'rule of inverse squares' principle.)



Hopefully that alone will resolve the problem but if not (because your studio space is too small for example) you need to consider some kind of French flag to shield the backdrop from the light source, or simply 'feathering' the light so it still spills onto the subject, but not on the backdrop.



Once you get it right, by metering your settings you now have a ratio... by changing all the settings equally you can get the overall level of lighting right for the particular DOF you want. So let's say you now have an aperture of F11, you can drop the power down on all the units by 2 or 3 stops, until you get to something more appropriate for your needs such as F4 or F5.6.