How to get a thicker soup from watery tomatoes? I want to make a tomato soup, but my girlfriend tells me that, from the tomato we have, the soup will be too watery. Now I've read that one could use tomato paste/puree as a thickener, and still keep a rich tomato flavour. But what would be the right dosage of paste? Is there any other advice/method to make a good tomato soup from my watery tomatoes?

UPDATE: Thanks for all your answers, unfortunately the most accepted answer seems to be quite time consuming, and I won't have that much time before tomorrow, the big day. It's my fault really, as I should have told that I had some time constraint. However, I want to try @Michael's solution another time, as it seems really interesting. In any event, I'll give a further update the day after tomorrow.
One thing you can do is dry off much of the water by slow-roasting the tomatoes in the oven first, similar to what I do in this risotto. I think you will get a more complex flavor than if you boil the heck out of them in a pot to reduce. I was also going to suggest pureeing them and then hanging them in a cheesecloth bag to drain the water, but you'll lose too much flavor that way.