I have a L 100mm f2.8 macro, which I have been using for my macro photos, however as we all know these lenses have a very narrow depth of field when used at close range, eg at 30cm,unless stopped down to very small apertures.
On this particular lens for instance on the 7D at 30cm the depth of field is 0.25cm.
As I have a 70-300mmL lens I was considering using this with extension tubes so that I could be further away from some subjects, but I do not know what happens to depth of field when using these with long focal length lenses. Can it be calculated?
Can anyone enlighten me?