Water bubbles

Hi, I intend to photograph my boy while he enjoys / plays with water bubbles. I want to know the things, I should keep in mind to get the desired output:
- the bubbles should be sharp and clearly visible in the pictures
- the background should be completely blurred
- the bubbles should reflect the rainbow effect ...you know layers of colors on the bubbles
- there should be stark contrast between the background and the bubbles

Yes I know I can do trial n error, but for sure the kid will not allow me a second session and I will not have sufficient time to run the trial.

Please help.

That's a tough one. If you want the bubbles and your son in focus you will need a smallish aperture like 5.6 but that will increase focused on the background so you need to increase distance between subject and background. Colours in the bubbles will be hit and miss as it depends on many factors like how much soap is in them and the angle of light.

Thank you for the inputs. Is there a way I can include a flash to create the rainbow effect with it on the bubbles?

I'd go with the bubbles and your son in sharp focus and then use an adjustment brush so you can bring down the exposure or really drop the clarity on the background so you can get some subject isolation even if you have to use 5.6 or smaller to get everything in focus.

I think you must have a good camera with great shutter speed. A few clicks and it can make the bubbles sharp.