how to blurr objects behind glass without blurring the light that falls on the glass?

How would I be able to have a crisp light falling on a glass object while objects behind the glass are blurry? I’ve tried roughness but it affects both the light and the glass. Playing around IOR but that just distorts it more and doesn’t blurr things behind the glass. Any idea how i can achieve this? Thanks!

Do you have an example (photo or else) of what you need to achieve?

Not enough information, so I have to make assumptions:

  1. I assume you use cycles
  2. I assume you use Glass Shader.

If so:
Instead of this you can use the mixture of refraction and glossy. Mix them using fresnel.
Because you have a mixture you can control them separately. Use low roughness for glossy to get sharp reflections of the lights and bigger roughness value in your refraction shader to have “blurred” background behind your glass.