In short: Astrophotography relies on trying to let the most light into your camera before the earth rotates too much and the celestial bodies begin to leave streaks- which is typically under 30 seconds, depending on your lens.
Finding a Dark Sky
Mastery of your camera makes absolutely no difference if you aren’t shooting in an environment with very little light polution.
Shoot Without the Moon
Ideally, you shoot between sunset and moonrise.
Don’t Forget the Weather
Living in California as I do, it becomes very easy to forget that weather exists. The skies are generally clear at night here, but when travelling this isn’t the case. Additionally, wind storms in the desert (the darker spots of California) kick up quite a bit of dust, which can become a cloying haze in even simple astrophotography.
Avoid Light Pollution
This is simple, check darkskyfinder.com and find a place that is very, very dark. Interestingly, these line up with ghost towns with some frequency.
Your Camera Settings
To better understand astrophotography, you need to assess the ideal settings, and then understand why those simply won’t work. Then we can dial in actual, pragmatic settings that will work.
The Ideal Settings
You want those stars to be sharp as possible, right? And your lens likely has the best ratio of sharpness to focal depth at f7.
You want to let in as much light as possible, and with such a low ISO, you probably want to be
You want as little noise as possible, because in post, trying to differentiate between faint stars and noise may become difficult. Minimize noise by setting the ISO as low as possible, and the lowest possible is ISO100.
Try these settings, and see what you get. Blackness, with no stars. Clearly these settings don’t quite work, but we can reasonably assume that the two most important settings are the shutter speed and ISO.
Actual settings that work
Open up that aperture as much as possible. You are desperate for every bit of light, so open it up as far as the lens will allow- f2.8 or lower, if you can.
Here you’ll need to use something called the “500 Rule”. Simply put, determine your maximum shutter speed time by dividing 500 by your lens’ focal length. I like to shoot on as wide a lens as possible for this reason, and with my Rokinon 14mm, I can shoot at (500/14), or 35 seconds. I cannot recommend the Rokinon 14mm enough for astrophotography.
You very likely need to set this near your camera’s max, try around ISO3200. The lower the better, obviously, but
Try to hit an Exposure Value (EV) of -7
The exposure value is a universal number for how bright something is. There’s a formula to calculate it. You don’t need to know it. You can use a calculator, and with a more in-depth explanation of astrophotography!
Consider your foreground
You might find that shooting the dizzying expanse of the milky way gets old quickly- without capturing the environment you are experiencing it in, often these shots lack impact.
Consider tree silhouettes, models on rock outcroppings, or interesting structures.
Think about painting the environment with flashlights, or sprinting around firing your flashes during the long exposures.