DP-Rainbow

Today I found that taking a shot of a rainbow is quite difficult. I saw a rainbow over the rear of my house this evening after a rain, and thought that it would be a good opportunity for a pic or two. Well, after trying multiple settings and more shots than I'd like to admit to, the rainbow disappeared before I found the perfect shot. Each shot looks grainy, and unfocused. I would like to figure this out at some point and get a good rainbow shot. Not biggie right now, just a few minutes wasted and not much to show for it. I've wasted more time on less useful things I guess.