I posted this on FM and thought I'd share here too...
It was kinda slow today so I decided to compare my D.I.Y. light modifiers. It wasn't exaclty a formal test, but it shows the difference. Distance to subject was appx 5 feet.
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Flash (580EX) was mounted on camera and rotated 90 degrees to facilitate fast changes from horizontal to vertical orientation, except for the mini softbox which was held off to camera left and slightly above the subject.