Nothing wrong with using off camera flash. Here are two coins, I used off camera flash with an Omni.
One word.....SCANNERIt shows a lot of detail But NO luster,
I just go by the idea that it's digital, take lots of pics and one or two will surely turn out nice. Delete the rest. I use outdoor light for some, flourescents for others. That just depends on the coin.Oh, and my camera is a Sony DSC-H5 with 7 or 8 megapixels, can't remember. It has a built-in macro, so that helps.