Alpha map problems with frosted glass

[ctz]

I'm modelling some flats which have frosted glass in the balconies. Some of these have the environment directly behind them. I plan to composite the model into a digital photo and what the digital photo slightly visible thru the glass. I render the image as a tga with an alpha channel & I can't get the effect I want.

If I tick affect alpha in the materials I get this -



If I untick affect alpha I get this -


(the red is the environment I used to create this example)

Can anyone tell me what I'm doing wrong?

[egz]

I believe affect alpha doesn't work with glossy refractions. You'd be better off rendering the glass without the glossy effect, and then blurring the background image in post to get the same effect.

[ctz]

Thanks Torgeir!