Astrophotography Lense

I'm looking to upgrade to a good Astrophotography lens but I don't know anything about them. I've read a few things...
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Dark Horse

Here's my first go at using a star tracker to shoot the core of the MW. This was shot at 70mm, with an exposure time of...

Rustic Fence

Shot in New Zealand.
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Crashing Waves

Santa Cruz, 2017