Saw a rainbow, but it was mostly obscured by the lower branches of a young fir tree. I grabbed the camera (mounted with a 300 mm lens), turned it on and checked the settings on my way up the stairs to a corner window. The settings looked OK so I focused on the tree top and got this image. Less than a minute later, the rainbow was pretty much gone.
technical:
ISO 400
aperture: f/7.1
shutter: 1/1600 sec
aperture priority
300mm 2.8 lens
These settings were initially intended for quick/stealthy wildlife photos (like the first deer on this page) out the office window. So for me at least, having the camera nearby and ready to shoot quickly in most light situations can make the difference between getting and not getting a useable shot.