DK-17M Magnifying Eye Piece
Many of the larger Nikon DSLRs (D700, D3, D3s, D3x) will take
the Nikon DK-17m magnifying eye piece. They cost about $40 and
simply replace the original eye piece. The DK-17M offers 1.2x
magnification which I find very helpful for close work. I put them on
all my cameras.