I wonder if someone out there could help me, please, with the following question.

suppose you have a 100mm, a 200mm and a 300mm lens.

Suppose these lenses have minimum focusing distances of approximately 1metre, 2 metres and 4 metres apiece.

Now you interpose a 50mm extension tube between each lens and the camera.

You should be able to get a maximum magnification of 1:2, 1:4 and 1:6, respectively, OK?

Well, how does this affect the minimum focusing distance in each case?