Warren, what big, slow moving, natural objects are there that warrant taking pictures of in the dark? increase the speed of your shutter to allow more light into the camera however this may cause a blur if the very slow moving thing moves too much. Increase your aperture, this will loose depth of field so try to work out a good balance between low shutter speed and a higher aperture. The lower the ISO the less sensitive the film is to light so in light rich environments a low ISO works well, the problem you will find is the higher the ISO the more grain you will see in your final picture due to the camera adding digital gain into the picture.
But in all honesty what large, slow moving, naturally occurring, nocturnal creatures are you taking pictures of?
