[dylan604]

>Full frame sensors have thin depth of field.

...when they have a large aperture. Stoping down the lens will widen the DoF on that full frame sensor

>so with big DSLRs you have to do focus stacking

you don't have to. only if that is the style you are wanting to achieve. you can also stop down the aperture. it's not as obvious as non-macro, but still something doable.

[jychang]

Have you ever stopped to think about HOW MUCH wider the DOF is when you stop down on a DSLR? Because when it comes to macro, the answer is "usually not enough", even at f/22. And at such small apertures, diffraction becomes a big issue.

This is why focus stacking exists for macro on DSLRs, as when using a true macro 100mm lens you basically have only a thin sliver of usable DOF at reasonable apertures.