Pillé sur le site de nikon us :
What is the difference between the SB-28 and SB28DX?
The SB-28DX is designed to provide fully dedicated TTL operation with the Nikon D1, D1H, D1X, and D100 SLR digital cameras. The SB-28DX is also fully functional with film-based cameras like the N90s, F100, and F5. There are no advantages to using the SB-28DX instead of the SB-28 with film-based cameras.
Salut. Avec ton F5, que tu utilises le sb-28 ou le sb-28dx ne change rien, les deux flashes fonctionneront de la même manière sans avantage ni inconvénient pour l'un ou pour l'autre. 8)