How do you do astrophotography with a telescope?

Many people, like myself, when I began this journey into astrophotography, started with a telescope and find that it would be a great idea to photograph what they see. The reality of moving from observing to photographing the images from a telescope involves a lot of time and experimenting to get right. It is a steep learning curve!

Let’s suppose that you have got yourself a telescope and made your first observations with it. You are probably wondering what you need to do to set up your telescope for astrophotography. Well, stick with me here and I will explain how you can get started with your equipment and set everything up so you can take your first images in this amazing hobby of astrophotography.

To set up a telescope for astrophotography, you first need to attach a camera to it and check if it is possible to focus on stars or the Moon. Your telescope may need modifying to allow you to use a DSLR. You’ll need a sturdy tripod or mount and set your camera correctly for night photography.

The above sounds quite straight forward but believe me it is not if this is your first time trying to do astrophotography. You’ll really only learn how to do this by following what I explain here, by doing research online, and by trying this yourself with your equipment.

So keep reading as I explain each of these steps and guide you along so that you can begin imaging in the shortest time possible and avoid any serious difficulties. It’ll be like having me alongside you as you try to solve the next challenge.

How to Attach your Camera to your Telescope

This was one of the most tricky things to solve for me at the start because my Canon DSLR did not connect to any of the parts of my telescope. The solution was to buy an adaptor that screws to the camera face where normally you would attach the lens. This allowed the camera to correctly interface with the wide opening of my focuser where I could attach the camera to my Newtonian reflector (Celestron 130slt) telescope.

You might be wondering about what kind of camera you can use for astrophotography, so go visit this page I’ve written to answer this: do you need a special camera for astrophotography?

Once I attached the camera, I found that I could not reach focus. I needed to modify my telescope because, like many scopes, it is designed for visual use rather than astrophotography. The modification needed is to move the larger primary mirror physically about an inch or so forward. The primary mirror in a reflector telescope is the one at the back of the telescope. Rather than saw the telescope tube and move the mirror I found a simple and reversible solution for this here.

If your telescope is already designed for astrophotography then when you attach a DSLR you should be able to focus. Remember the best way to connect your camera is to use prime focus. This way the camera will not be at the end of a long tube and adding extra weight to your telescope. See the diagram below for a quick explanation of what prime focus is.

What Kind of Mount Do You Have?

There are two main kinds of telescope mounts, but it is important to know which kind you have as this will change how you need to set it up.

The first kind of telescope mount is Alt-Az and the second kind, which is more complex to set up is the equatorial mount. I started with an Alt-Az and then upgraded to an equatorial one.

Celestron 130slt az-alt mount
My first az-alt mount with DSLR

The basic difference between an Alt-Az mount and an equatorial one is that the first has a mount that can move in two directions, horizontal and vertical. Therefore it can go to any point in the sky but cannot follow the same exact path that the stars and other celestial objects follow.

An equatorial mount rotates around a point that needs to be set parallel to the earth’s celestial north pole. The rotation of the mount is opposite to the rotation of the objects in the sky such as the stars and other deep sky objects and therefore counteracts this movement. In essence, the equatorial mount freezes the sky and enables us to image objects for many minutes at a time with no star trails visible in the image.

By using an Equatorial mount I have managed to take sub-exposures of up to 15 minutes or more with nice round stars. When I used my alt-az mount, (Celestron 130slt goto telescope), I could only manage 30-45 second sub-exposures and therefore had to take many more photos to image my object. Longer sub-exposures make it possible to save space on computer storage because you have fewer photos for the same total integration time. Longer sub-exposures can also bring out more detail in the final image when all the photos are stacked together.

How to Setup an ALT-AZ Mount

This kind of mount is one that beginners often start with as it is simpler to set up. The only thing you need to do to set it up is to align the telescope with two or three stars so that the internal computer has a map of the sky and knows where it is pointing. This alignment normally involves placing the star in the eyepiece centre and then using the Goto hand control to enter each alignment point.

This is all that needs to be done to set up an alt-az mount.

How to Setup an Equatorial Mount

This kind of mount is usually more expensive because it is designed to track the motion of the stars more accurately than an Alt-Az mount and can help you to achieve longer exposures without star trailing.

The setup of this kind of mount involves first setting good Polar Alignment so the mount is set to be parallel with the celestial north pole around which all the stars rotate. This can be done using a small polar alignment scope on the mount or by using a program such as Sharpcap Pro. This is currently the method I use and enables me to align to within a few arc minutes.

The mount must also be set to a zero point where it is facing celestial north. This is done after Polar Alignment. The mount software needs to know the GPS coordinates of the location where you are and the Equatorial mount is correctly Polar Aligned when the latitude angle is correctly set on the mount (part of polar alignment).

Taking a test shot of your target will quickly confirm that everything is set up correctly as you should see no visible star trailing.

How to Setup Your Camera

The main setup for your camera once it is correctly attached, is to choose the appropriate settings ie. ISO, exposure time, pause between shots, and set manual focus and bulb mode. Sounds quite a lot, doesn’t it? But don’t worry! It gets much easier with time.

If you use a DSLR camera, you’ll need to set Manual Focus, White Balance to auto or daylight, ISO should be set to the best value for your camera which you can find by looking this up online. For my Canon 600D this is 800 ISO, but could be 1600 ISO or some other value for the camera you have. Set the camera to Bulb mode so you can shoot longer than 30 seconds. I’ve written this helpful page with more detailed information about the correct settings for exposure.

Focus is one of the most important settings to master and did give me a number of problems. First, find a bright star to focus on and do your best to get it as small as you can using the Live View Screen on your DSLR. A Bahtinov mask is also helpful for really pinpointing focus. You may need to check focus again after a few hours, depending on your equipment and conditions.

What Else You’ll Need to Setup for Imaging

intervalometer
An intervalometer

You’ll also need to set up something to help monitor and plan the images that you intend to take. This could involve an intervalometer or software such as Astrophotography Tool.

As you progress in your journey, you may also wish to start using guiding to extend your exposure time to many minutes at a time and this will require further setup of a guide scope, guide camera, and software such as PHD2.

In Conclusion

There are a number of things to get right before you can start to image astrophotgraphy targets successfully. Basically, this involves understanding the equipment you have and the basics of photography. This will enable you to set up your telescope and attached equipment so that you can begin to take photos of deep sky objects, and as you learn more your images will improve step by step.