You can't get decent results but aiming a lens at the moon and triggering the shutter.. Stack a 1 stop and a 2 stop ND filter in front of your glass. Use a 400 with a doubler, manual focus, fire some frames. You get the picture.. There is one I shot of the moon tonight on my blog.
the Iconic Image
There is absolutely NO reason to put any type of filter in front of your lens when shooting the moon. If your shot is overexposed, shorten the exposure time. The moon is never any brighter than an earth scene in the middle of the day. They are both lit by the sun and are both the same distance from said sun.
Some basics:
Get the longest lens you have. Sometimes a slightly shorter focal length prime is sharper than a longer zoom, so keep this in mind. Experiment.
Set the aperture to its sharpest setting (usually 2 stops slower than wide open).
Depending on how sharp your lens is, you can put a teleconverter on it too. Keep in mind this greatly reduces the light and sharpness, so if you can already see the softness of your lens at max zoom, there's no reason to amplify the softness with the teleconverter.
Now choose ISO and shutter speed. It's somewhat of a balancing act if you're handholding the shot, but if it's a tripod shot and you have some kind of remote, timer, and/or mirror lock up, then go with ISO 100 and adjust shutter speed accordingly. If handheld, make sure your shutter speed isn't slower than 1/F.L. In other words if you have a 300mm lens, shutter speed shouldn't be slower than 1/300th of a second. Adjust ISO accordingly.
It's very basic stuff with exposure. If you have a white ball, it's overexposed. If you have a black screen, it's underexposed. The histogram is your friend, but it's easy to see visually too.
It's best to shoot the moon when it's at least 45 degrees above the horizon - less atmosphere to shoot through and therefore less risk of distortion at higher focal lengths. Happy shooting.