Plus an optional item.
The first is probably obvious. You’ll need a tripod. Or a stable surface. It’s nigh impossible to hold the camera rock steady for a long period of time. If you don’t have one, don’t get just any tripod from Walmart. Those are cheap and flimsy, and a stiff wind can be enough to jostle the camera. I highly recommend the Slik Pro line. They’re pretty budget friendly, ranging from $100 to $250. If budget isn’t an issue, check into Manfrotto and Bogen.
The second? An off-camera locking shutter release. No matter how gentle you are, when you press that shutter button and release it, it’s going to jostle the camera. Get a shutter release cable with a lock on it.
Alternatively…I was reading my manual recently and discovered that my Pentax k5 has a feature where simple wireless shutter release will work similarly – press once to engage the shutter, press a second time to disengage. So if you already have a wireless shutter remote and a relatively new camera, check your manual to see if you’ve this feature.
While you’ve got your manual out, if you’re unfamiliar with the “bulb” mode, find the section in your book about that.
The bulb mode is what allows you to keep your shutter open for very long periods of time. Many minutes. An hour or two, even (though some of the older dSLRs will time out after 30 minutes or so).
Why shoot in the bulb mode?
For pictures like these.
The optional accessory is a ND filter. These filters let you take “extremely long exposures” in daylight, instead of restricting you to nighttime. If you’ve ever tried to take long exposures in daytime, you probably know what happens: stark white burnouts.
I have the ND-100 (about 6 stops); it’s perfect for gray overcast days, which we have plenty of here, or early mornings/late evenings. The ND-110 (10 stops) and ND400 (9 stops) also come highly recommended.
There are kits where you can stack filters to increase the number of stops. However, it’s my understanding that there can be distortion from so many layers of plastic/glass in between your lens and the actual subject. I wouldn’t recommend these.