I was out today shooting a cattle roundup / vaccination / branding on a friends ranch. I was using the above mentioned cameras, the DF with 24-120 f 4 G ED, the D 750 with 28-300 3.5-5.6 G. Both were set to P, full sun, Vivid, -.3 ev, 400 auto iso. The action was fast and furious. When I was not helping with the work, I was shooting. I shot about 190 shots between the two cameras in four and a half hours. The D 750 battery reads as new, the DF battery is about a year old, both were fully charged when I started. I was shooting some fast sequences, but with shutter set for single frame, so doing it manually as I have always done. I had 3 scattered black frames on the DF, five on the D 750, with one group of 3 in a row where I had landscape, portrait, landscape orientation. On my last trip a had a couple, didn't pay much attention to which camera. I do shoot from the hip sometimes, but as soon as the camera comes out of the bag, the lens cap is off and stays off till I put the gear away. I have quality clear filters on both lenses. I bought the DF New Summer '14, the D 750 used with low exposure count last fall. Neither is anywhere near rated shutter usage. Though I haven't recognized problems, I was already thinking of sending the DF back to Nikon for general servicing. The D 750 is Gray market. I cleverly deleted the photos, but may be able to dig them out of the Trash. Any ideas, similar experiences, suggestions?