How to make a transparent flow

I wonder: is there an easy way to giveone side of an object another opacity then another side. There should also be a flow between the 2 opacity's. The only way I can think of is doing it "manualy": by cutting it in slices with different opacity or using the gum-tool with a low opacity... But I think it's very hard to get good results that way...
Grtz, Doody!

Not quite sure what you want to do, but a gradient mask should work just fine. Or at least if you wanted to do it manually, then grab a big fuzzy brush and paint on the mask.

Layer > Add Layer mask and then either use a brush or the gradient tool (set to black-white).

Thx, man. Exactly what I needed :D