Seleukid coin, with suckling foal

A coin from Ekbatana in the Seleukid Kingdom, reign of Antiochos III. (223-187 BC). Coin legend (in Greek lettering) ΒΑΣΙΛΕΩΣ ΑΝΤΙΟΧΟΥ and it shows a mare standing left, head reverted toward suckling foal with a monogram to the left. (The Seleukids were apparently famous for horse rearing). The coin is 19mm across.

Nikon D40 mounted pointing down on a Velbon CX-460 mini tripod. Micro-Nikkor 55mm f/2.8 with a close-up lens (the one from my Cosina Voigtlander 40mm f/2) attached. ISO 200, 1/40s, f/11 to get the depth of field. ML3 remote.

I don't yet have a separate flash; this was taken with the pop-up flash on the D40 plus a 'puffer' diffuser. Since the D40 does not meter with AiS lenses, exposure was by histograms and flash was manual, at 1/8 power. A mirror was used as the background.

Overall moderately pleased at this shot, except for a white halo behind the coin at 11 o'clock. Presumably this would be avoided by a better flash position?