Hi Rob, Unfortunately I had to make several lens changes when I was shooting this past summer in the Cripple Creek goldfields. Not only that, but the area is pretty dusty. But I'm extremely careful about lens changes, especially in the field, where I hold the body with the opening down, and blow off the back of the lens with a hand blower before I attach it. Considering its size and softness this particular spot may not be dust. Every Nikon DSLR I've had: the D100, D2x, D3, and D800 has started its life by occasionally throwing lubricant on the sensor for the first couple thousand shots. I've always thought it was oil, but I've been informed that it's a dry lubricant, maybe like powdered graphite. I suspect I'm not out of the lubricant phase yet with the D800. The D3 finally settled down and I didn't need to wet-clean its sensor for about four years. I've wet-cleaned the D800 at least 3 times, and I suspect it's time to do it again. One problem is that when I shoot a blank, blue sky at small aperture, the color version of the shot doesn't show a problem. It's only when I convert to B&W that the problem starts to show up. And even then, it's easy to miss a spot. But I should have seen the spot in this picture.
And yes, the D800 has a "shaker," but in my experience it's been almost totally useless, unlike the shaker on my Olympus E-P1, which really does the job. On the E-P1, though, I almost never change lenses. It lives with its 25mm Summilux, which is the equivalent of a 50 on a full-frame.
Yes, hairs in the gate is pretty technical stuff. I suspect someone who's never worked with film cameras might think it's obscene.
