how do i calculate wxposure on a manual ringflash?

[Michael_I]

Is the usual guide number/distance=f stop applies in usual photography and how does it work with macro?

How do other(then 50) focal lenghts affect exposure?

thank you
Mike

[OleTj]

the usual rule still applies. BUT: with macro, you have to take light loss from extension into account, the so-called "bellows factor".

Focal length makes no difference, only the magnification.