Sigma EF-530 DG Super Electronic Flash for Nikon DSLR Powerful Guide Number of 174 ft / 53m at 105mm Setting Designed to work with the new TTL systems of all the popular manufacturers Fully compatible with all Nikon Digital SLR cameras including the D40 and D40X Covers a focal length from 24mm to 105mm Autozoom function automatically sets the optimum illumination angle.