Alpha on transmission

Hi, I’m new to blender, and when I’m using a transmissive material like glass or water I can’t find an option to make the material output affect the final render’s alpha channel, like when a ray doesn’t collide with anythig after being refracted it would return black, for reflections it would return white, for absorptions and volumetrics, it would return the appropiated gray value.
Right now it always returns a solid white for the alpha.
Is there a way to work around this?

Thanks.

AFAIK any refractive shader is regarded as opaque as far as alpha is concerned - to capture the refraction. Use a transparent/glossy mix instead.

Yeah, that’s what I’d figured.
Thanks so much fur the quick response.