As students get ready for night photography workshops, they often ask the question, "If I could buy just one lens, are there any that would really help with my night photography?". On this, I smile because there definitely is. And the best part is the route I recommend doesn't break the bank.
In general, a wide-angle, bright lens with a minimum aperture of 2.8 would be ideal. Good night photographs come from lots of other lenses, but in general, the low light sensitivity of an f/2.8 lens makes capturing the starry night sky a lot easier.
Improving Low-Light Capability With A Better Lens
Just like a new camera body can gain a few stops of low light sensitivity, it's well worth taking a look at how lenses can do the same. As an example, changing from an f/4 lens (a lens with a minimum aperture of f/4) to an f/2.8 lens is equivalent to doubling the amount of light you have to work with - which is a big deal. And a lens with an even wider aperture like f/1.4 can give you even more low light sensitivity...