The reason we need a large lens is that the Moon is tens of thousands of miles away. I know it’s large in size but it still appears small in the night sky. At 300mm we should be able to make it fill about an 8th of the frame. If you can get a 500mm lens all the better but it can be expensive to pick up these really large lenses. A way around this is to look for a place to rent Camera Lenses. There are a lot about and will do you good deals if you only need it for 24 hours. Great if you plan it around a Full Moon. It’ll probably be as cheap as $30 and no more than $50 if you go for as big as an 800mm Lens.