posts fading

hello, how can I switch off the post thumbnails fading (when mouse over a post in the post-loop, the post picture fades and shows post-information)

I just want to use the instant fading like:

post-info: opacity = 0;
post-info -> mousover: opacity = 1;

///// and I don’t want to fade them like animation.
how can I do it? digging style.css hasn’t shown any timing;