Non linear gradients?

[sams]

I am trying to use a large image as a bg for poster and want to have a gradient that will go from 0-30% opacity over the first 3/4 of the image and then from 31-100% opacity over the last 1/4.

I tried to move the midppint in my gradient editor to 85% in order to acheive this affect, but, it made no change in the image. I have tried this with both raterized and smart images and watched every video on youtube. What am I missing?

sam

 

[Hoogle]

create a new layer select the gradient tool with black to transparent and then play with it until you get it right from where you start and finish