Why do my tomatoes dry up prematurely?

Question

Do they have a blight?

Answer 1

Is it the tomato fruits or the tomato vine and leaves which are drying up?

Check this article for fruit problems:
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/visual-guides/tomato-fruit-problems.aspx

Check these articles for vine and leaf problems:
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-diseases.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-plant-problems.htm