I can't keep my backgrounds white!

[Scurra]

I'm going to be shooting a series of fashion shots tomorrow however I can't keep my background white, at the moment the set up is 2 interfit halogen hot lights with one diffuser brolly and one reflector brolly to light the subject and 2 smaller workmans halogen lights to light the background which in this case is a white sheet stretched over a custom built frame. I tried intentionally overexposing the images by a couple of stops and it results in a still slightly off white background and a blown out subject. I have set the white balance according to the manufacturers spec Kelvin for the lights we have also.

These are full length model shots by the way and i'm shooting on my Canon 20D, i'd like to be able to avoid a lot of photoshopping as i'll be shooting in excess of 100 images. Any ideas on what I can do to sort this out would be much appreciated.

 

[ferny]

Sounds like there simply isn't enough light on the background. The only answer is to over light the background and metre for the models or Photoshop.
Speaking as someone who knows sod-all, you understand.

 

[Big Mike]

As far as I know....ferny has it. You have to have more light on the background. You want at least 2 stops brighter than the model.