D800 - Not much better then my D300s, what am I doing wrong?I received my D800 but th

mrwilkins wrote:

Looking at those two photos side by side scaled to the same size, I can see a distinct overall softness in the D800 photo that's not in the D300s photo.

There are multiple things going on here -- your lens is at a different focal length between the two images, which wide open might cause a difference in sharpness. The larger FX sensor has a shallower depth of field at a given aperture. There may be vibration going on, and as others have pointed out, 1/8 second is just about the worst shutter speed for vibration when using a tripod.

That said, the fact that I can see a difference in sharpness at even at a reasonable screen viewing size for each full image tells me that one of those issues is causing you problems in this comparison. Mirror lock-up, using a higher ISO to get your shutter speed up, or shooting a test scene in brighter light that gives you a fast shutter speed at f/8 or so all would give you a test that's less susceptible to issues with technique or performance of your specific lens at different focal lengths.

Edit: One other factor is that you have to go 50% longer on your focal length to get about the same FOV on the D800. This in itself amplifies the effect of vibration, by magnifying it when you zoom in.