Struggling with white backgrounds

[noz03]

I do quite a lot of white backgrounds but somehow still feel like I am struggling with them... I don't have enough lights to put 1 each side so usually put just 1 speedlight in the center with a diffusion dome on it to spread the light out, I know it is not ideal but it's what I have to work with for now. Then I take a shot and try to get the background ALMOST pure white on the histogram and take it down to pure white in photoshop later. There are mostly two problems I keep coming up against though, I of course lose a lot of contrast, although I know how to fix that in post, and the biggest problem is the edges become a bit weird, especially around peoples hair.

Here is an example without any editing:


So I would like to ask...

Is there anything I could do to get this better in the camera with my equipment? I don't mind doing some editing but I'm sure I can do better than this in the camera...

Secondly... What can be done in post for the edges? I don't even know how to describe them but as you can see they look horrible

 

[Garry Edwards]

Just move your subject further from the background, the distance is inadequate and this is the cause of the problem.

 

[Faldrax]

Hopefully one of the experts will be on to give a definitive answer, but from my limited understanding your problem is the light being reflected off the white background back onto the back of the subject.

If possible more the subject further from the background - even a relatively small change may make a noticeable difference, due to the inverse square law.

[Edit: Gary got in while I was typing - he's one of the experts I was referring to ]

 

[noz03]

Thanks for both the replies

Well she was a bit close but to soo much, I'd say 2 meters from the background but my room is only 4-5 meters long so that's about as far as I can go :/ Another time I had to take a white background in a room even half this size though! That was a nightmare... The light literally shone through their ears although the edges somehow weren't as bad as this one. Maybe I had the light on too high power? Although then I would end up with a light grey and quite dark edges.

 

[Faldrax]

If you can't move the subject further from the backdrop, can you move the light closer to it and still get the even coverage?
If you have a diffusion dome on the speedlight, is any light spilling from the speedlight direct to the back of the subject - if so, flagging that might help a bit.