Astronomers drove digital imaging sensitivity, so I reckon they’ve got it worked out. Skimming http://arxiv.org/pdf/0709.4281v1 , it looks like Ralph, the main visible-light camera, can distinguish between true blackness and a mere 3k photons per pixel, and at the margin can detect objects of magnitude 14. Coincidentally, that’s about the magnitude of Pluto from earth, and you can’t see it even with a small backyard telescope. So this instrument is less like a consumer camera and more like, say, night-vision goggles.

This paragraph originally did the math for Pluto’s brightness wrong (thanks to atakan_gurkan below for pointing that out), so instead let me refer you to a short but interesting Metafilter thread on exactly this question: http://ask.metafilter.com/23197/Darkness-at-the-edge-of-town .

One more factor – Pluto’s albedo is quite high. It reflects 0.5 to 0.66 of the light falling on it, as opposed to e.g. 0.14 for the moon (which is fairly dark in the scheme of things, but not at all hard to photograph; you can easily overexpose it in a grainless photo with a recent consumer DSLR).

So: dim, yes, but still clearly visible.

Brightness drops off inversely proportional to the square of the distance, not square root.

Still, I think there will be plenty to see. I am quite excited about this actually.

Fantastic replies. Thanks all. Very excited to see what's out there.

My understanding (which I got from an astronomer looking for moons) is that it'll be enough to get a clear look at major features on most (not all!) of Pluto's surface, but nothing spectacular. Realize that even today, we don't really know what Pluto looks like, so any knowledge is big knowledge.

There are some images from Hubble:

http://en.wikipedia.org/wiki/File:Pluto_animiert.gif

Pluto only fills up a few pixels on Hubble's camera, but it's possible over time to generate a rough image:

http://www.boulder.swri.edu/~buie/pluto/mapstory.html