If you want to take a good picture, you need a solid mount. Here's some considerations to keep in mind.
How a Mount Works
I use a Sky-Watcher EQ6R Pro mount to hold my time machine. This is a German Equatorial Mount (GEM) that looks a little wonky when you first see it, but makes more sense when you understand how the Earth rotates and how we describe where things are in the night sky. Another type of mount is called an Alt-Az mount (short for Altitude-Azimuth) and might seem, at first glance, to be easier to move around, but for taking pictures, you'll want a GEM. Let's delve more deeply into what a mount does besides keep your telescope from lying on the ground.
How the Earth Turns
The Earth spins approximately 360 degrees every 24 hours. We call this one day. In reality, the number is a little different, but we're not concerned with that right now. For our purposes, it's fine to say "the Earth turns 360 degrees in 24 hours." We often think that the stars and planets above us are moving throughout the night, but in reality, they're motionless and we're moving as the Earth turns under our feet. In 1 hour, the Earth will rotate 15 degrees. That's about the length of your outstretched hand from fingertip to fingertip, according to this great chart from timeanddate.com.
In six hours, something that was on the eastern horizon is now overhead, and something that was overhead is now sinking below the western horizon. We think we're standing still while those things move, but in reality, it's the other way around. Either way, if you're going to take a picture of something that appears to move, you need to counter that movement to make sure that the object stays still in your picture.
That's where mounts come in.
Alt-Az Mounts
Any kind of mount can track an object so that it stays in the field of view of a camera or binocular or other Time Machine. An Alt-Az mount is the easiest to think about because it basically rotates left and right, and then up and down. That's essentially how we view the world. We look left and right by turning our heads, and then we look up and down by moving our neck or leaning backwards. If you have a pair of binoculars attached to your hands, then you become the mount as your body moves. You are countering the apparent rotation of the night sky, and you are keeping the object in your field of view by moving your body. A mount has to do it with motors and electronics.
While an Alt-Az mount can track, it can't really do it well for a long period of time due to something called field rotation. In short, this is an apparent rotation of the field of view of an object being tracked in an Alt-Az manner because the sky isn't moving in a left-right/up-down fashion; it's actually a rotating sphere. So over time, an object will appear to rotate in the field of view of a camera on an Alt-Az mount if you let it track over a long period of time. It's also complicated by a number of other factors such as how high up the object is and where you are on the planet. In short, Alt-Az makes a great visual astronomy mount if you're going to be there to move, adapt, and adjust, but if you want to take pictures, you really need a GEM.
German Equatorial Mounts
GEMs are designed to sit at an angle that matches your latitude on the planet. If you're in New York, for instance, you're at approximately 40 degrees North latitude. If you set up your GEM there, you would have it set such that it's angled up 40 degrees from horizontal. This one small change allows you to aim the mount at the North Celestial Pole and now the mount can rotate just like the Earth does, and keep everything in line. If you want to find out more about GEMs and the celestial sphere, there are other resources. I want to talk specifically about my GEM mounts and why I use them.
Picture This - GEMs in the Sky!
The EQ6R Pro is a great mount for just about any kind of astrophotography. It can hold up to 40 pounds of equipment, it is well designed, it has a great hand controller if you don't want to connect a computer, and it's well supported by many pieces of software if you do want to connect a computer. Ask any Time Traveler and they'll probably tell you that they use (or used to use) one of these mounts. By putting your telescope and camera (or just your camera with a lens) on a GEM mount, your camera can take long exposures while the mount tracks the sky as it rotates. Without tracking, you can take exposures of about five seconds before the motion of the stars will make them start to look like tiny footballs on your image. With tracking, you might be able to go as long as 20 or even 30 seconds depending on how good your initial setup and calibration is.
And it's that setup and calibration that we're going to talk about now.