Hi Ian,
Making photographs at night can be very challenging, particularly if your camera is not getting enough light to focus with. The built-in AF illuminator is usually only good up to a few metres, but even then you do have the problem of potentially scaring away the subject you are trying to photograph.
One option to get around the problem is to rely on estimating the distance from the subject to the camera, and then looking for a bright subject in an equal distance that you can focus on (usually the edge of a window that has been illuminated from inside is a good option). Once you have done this, lock the autofocus (one simple way of doing this is to turn the AF switch to MF on the lens) turn back to your subject and take the photograph.
If you are using this technique, it is helpful to close down the aperture a couple of stops (down to f11 is a good option); this way the depth-of-field will help create for any inaccuracies in the focus.
As for how to improve this image; in the example below I selected the possum using the left Lasso tool and selected the feathering option to about thirty. I then added two Curves Adjustment Layers. With the first Curves adjustment layer I have pushed the middle of the curve outward to brighten up the possum. I have then used the same selection, inverted it and then used a new curves adjustment layer to darken down the tree.
Net result: it is now easier to see the possum!
Cheers, Anthony.
Image Doctor's edited version
