Another thing I've been wanting to try for quite a while... catch the thinnest of moons setting on a far horizon. This was done with the 500mm and really pushes the limits of low-light photography. You could not see the moon at this point, or for quite a while! Only visible in the shot, high ISO to cut down the exposure time which needed to be fairly short or the moon blurs from movement. Not a good "picture" by any means, but a lot of fun and does show where the lines are drawn.