Hi Folks -

OK, I'm shooting the northern lights with my friends Nikon D40 with a 10mm f/2.8 lens. We're in manual mode: ISO = 1600, f/stop = 2.8. I have the shutter speed showing 8 seconds on the LCD, but when I hit the shutter release, it's much much less than that (like maybe 1/30 sec or so). We're not using any flash. It was lighter last night (there was some moon out). The only way I can get the shutter to hold open for any amount of time is to run in aperture mode (which with our current lighting is automatically hitting around 10 sec). I'm wanting to tighten up the shutter speed so that I can get better definition on the lights (with 10 sec, there's some blurring...still pretty, but they look more like amorphous stripes).

What's weird is that this same setup worked fine in manual last night; now it doesn't. I've done the patented "turn it off and turn it on again" process, to no avail.

Thoughts? Things I should be looking at?