Semi transparent areas in cycles?

Support Lighting and Rendering
1

Hello everybody,
I am looking for a semi transparent render in cycles. I have A glas material with a slight reflection on it. I turned on transparent background and I want to composite it with another background image. I want the background image to show through a bit.
Is there any way to make something like this?

Thanks

Günter

2

Thanks everyone, I solved it with the holdout shader.