I've tried to do that myself with varying degrees of success. Turns out that you need a pretty fast film to do it well, and TMax 400 seems to have worked out the best for me. A full, or nearly full moon on a clear night comes in at around EV 13 or 14. With ISO 400 film, and with an aperture of around f/14 (that's the approximate "f" number of your "lens" if the focal length is 1250 mm with a 90 mm aperture), you'll need a shutter speed of between 1/250 to 1/125 second for a good exposure. Maybe a little over exposed at 1/125 and a little under at 1/250, but close enough unless you're being really anal about it. Even with a lens that long, the moon will only occupy a very small portion of the frame, so forget what your in-camera meter tells you. It will be unduly influenced by the expanse of black sky in the frame. And you do want to use a fast shutter for couple of reasons. First, and this is not to be overlooked, is the fact that the moon is moving across the sky more quickly that you'd think. Exposures longer than 1/60 second will show motion blur due to sidereal motion unless you have one of those mounts that can accurately track celestial objects as they move across the sky. You also need to allow for any other minor vibrations that can ruin your shot. Wind, camera induced mechanical vibrations, even passing vehicles can all induce vibrations that will show up when using a lens this long. Now if that's not bad enough, realize that because the moon will only be a small part of the frame, a high degree of enlargement will be necessary to fill a modest 8x10 print, further magnifying even the tiniest bit of motion blur and camera shake. Don't even think about slow, fine grained films. It won't work, unless of course, you have one of those fancy motorized tracking mounts. Then you might have a chance. Otherwise, go for something fast and don't worry about the grain. That's the least of the challenges you'll face. Sorry to burst your bubble, but that's the way it is.
