My 8 year old daugter loves science and things having to do with space. I would like to take a really nice picture of a full moon for her birthday, which is quite a while off. Currently, my longest lens for my Fm2n is 135mm, and I'd like to get a longer lens to get a better shot of the moon. I probably won't use the lens very much for other things, and so I don't want it to be excessively expensive, and I'll have to sell other equipment to finance it. What would be some good options?