How to Take Photos of the Night Sky Through a Telescope
You may have made your first steps in astrophotography by using only a camera, now you want to try to photograph the night sky with a telescope. Or perhaps you’ve just got a telescope and want to know if you can also use it for astrophotography.
Types of telescopes
First, we have to acknowledge that not all telescopes are the same. Some are better suited to astrophotography than others. Usually, if a telescope is suited for astrophotography it might not be the best visual telescope, and unfortunately, there’s no universal instrument.
We can divide telescopes into reflectors and refractors.
Reflectors use a system of mirrors to collect light but are often quite bulky and not very portable. They are more suited for visual observations or more advanced astrophotography.
Refractors use lenses as their objective. They are more compact but also more expensive per unit of aperture than reflectors.
Apochromatic (or APO) refractors use lenses built from special low-dispersion glass. APOs offer almost perfect chromatic and spherical correction for sharp imaging. They are more expensive than their achromatic counterparts, but they are worth every penny.
APO telescopes use 3 or 4 lenses in the objective. There is also a class of refractors called semi-APO or ED. They are less expensive than real apochromats and are probably the best choice for your first astrophotography telescope.
Good instruments to start with are the SkyWatcher 80ED or the Explore Scientific 80ED. Actually, almost any 80ED telescope out there is a good option. If you are looking for exquisite optical quality check out brands like Takahashi, TeleVue or CFF Telescopes.
We can also divide telescopes by the type of mount they are placed on. We can have alt-azimuthal telescopes (with Dobsonians as a sub-division) and equatorial telescopes.
Alt-azimuthal telescopes have a simpler way of moving (think about the way a cannon barrel moves) and are better suited for visual observations. Equatorially mounted telescopes will be able to track the apparent motion of the night sky and are the best choice for astrophotography.
In terms of equatorial mounts, you can get a super portable mount like the Fornax Mounts LighTrack II, the Sky-Watcher Star Adventurer or the AstroTrac. These small mounts will be able to carry a small refractor, using a special counterweight kit supplied by their manufacturer. If you want a more advanced and capable equatorial mount, look at Sky-Watcher EQ5, iOptron CEM26, or Losmandy GM8.
Ways of shooting through a telescope
The easiest way of shooting through a telescope is by using the afocal method. For this, we need a telescope with the eyepiece on and a camera with a normal lens attached. This was the first step in telescopic astrophotography during the days of film photography.
Nowadays, it’s easier to replace a camera with a smartphone. The photos might turn out better and it will be a lot easier to set up everything. You just focus the telescope so that you can see a sharp image in the eyepiece and then place the smartphone on top of the eyepiece. The only tricky thing here is to perfectly align the lens of your smartphone camera with the lens of the eyepiece.
With telescopes larger than 30cm in diameter, you can even try shooting brighter deep sky objects like The Great Orion Nebula. For shooting the Moon, you don’t need any fancy apps. The default photo app of your phone will be able to take some pretty impressive photos.
If you want to do deep sky photos with a large telescope, you need an app that allows for manual control of the camera in your smartphone.
As a general rule, don’t use very high magnification on your telescope. This will result in a fast-moving object in the field of view and blurry photos – unless you have a good equatorial mount.
Afocal imaging is easy and will allow for some beautiful photos of the Moon but, if you want to do ‘real’ astrophotography through a telescope, you need to connect your camera to your telescope. Basically, the telescope will be the lens of the camera.
This type of astrophotography through the telescope is called prime focus. As it would not be feasible to build telescope focusers with couplings for every camera bayonet out there, you will need an adapter from your camera to the focuser of the telescope, but more on this below.
If you want to shoot objects with a large apparent size in the sky, like The Great Orion Nebula, The Andromeda Galaxy or The Eta Carinae Nebula, a short focal length refractor will be the best. Such a telescope will also be the best choice for shooting total solar or lunar eclipses.
For planets or globular clusters, think about long focal length refractors (and large aperture as this will make them expensive) or Schmidt-Cassegrain type telescopes.
Read more: The Best Equipment for Star Photography
Telescope camera adapters
There are lots of adapters that allow your camera to be connected to a telescope. As we did before, let’s look at such adapters based on what kind of setup you will use.
For smartphone afocal astrophotography, you have a few options; from straightforward ones that will not allow any precise adjustments to very advanced ones with geared movements on three axes.
All such adapters will attach directly to the eyepiece of your telescope and allow the smartphone to move more or less precisely so that you get the best framing and focus. Be careful with balancing your telescope as some extra weight will be added by the adaptor.
A very simple one is the Discovery DSA 10 (you will find it under different names, but it’s the same product). This adapter will not allow for the most precise movements but will do the job with a bit of work on the user’s side.
Probably the most advanced smartphone adapter is the Celestron NexYZ. It has geared movements and allows for precise alignment of your smartphone camera to the eyepiece. It is also quite heavy and you need some care when attaching it to the eyepiece, but once you have it attached, you will align everything in a matter of seconds.
(insert celestron_smartphone.jpg Caption: The Celestron NexYZ adapter allows for very precise alignment)
When it comes to prime-focus astrophotography, the adapter world suddenly becomes larger.
First, you need a T-Ring to convert the bayonet of your camera to the universal T2 mount. A T-ring will thread and lock on your camera just like a normal lens does.
You will find a plethora of T-rings suited for any camera you can imagine, from very old film cameras to the newest mirrorless systems.
When buying this piece of gear, just be careful that it doesn’t convert your camera bayonet to an M42 mount, but a T2 one. M42 adapters are pretty common too and will allow you to use old M42 lenses on modern cameras, but they are not suited for connecting the camera to a telescope.
Then you need a T-adapter, which connects the T-ring to the telescope. T-adapters come in two types. One type will go in a standard telescope focuser, while the other will screw to the back of your Shmidt-Cassegrain or Maksutov telescope. The latter allows for the eyepiece holder of the telescope to be removed so that the camera connects straight to the body of the telescope, thus having a more rigid system.
However, unless you use a catadioptric telescope, you will need a T-adapter that fits the focuser of your telescope. Before buying a T-adapter, do check the manual of your telescope and see what kind of adapter suits the focuser of your telescope. Most of the time, you will need a T-adapter with a 1.25” or 2” barrel (nose-piece).
However, some telescopes are special, and need dedicated T-adapters. One example is my beloved Pentax 75SDHF which has a specific T-adapter that screws directly into the focuser.
There’s one more way of shooting through the telescope – eyepiece projection. This kind of photography appeals to astrophotographers that shoot high-resolution images of the objects in our Solar System.
When doing eyepiece projection, you use a special adapter that allows for an eyepiece to be fitted inside it. You then connect the camera to the adapter; your camera will photograph the image projected by the eyepiece.
Astrophotography through a telescope has its specific struggles.
Focusing, as in any type of astrophotography, is critical. Use the LiveView option on your camera to focus the system or, for even more accurate results, focus using a laptop (connect the camera to a laptop and focus using a dedicated piece of software).
If your telescope is way out of focus, first use a distant object (like an antenna or distant building) to achieve rough focus, then it will be easier to properly focus your system. If you are shooting the Sun (only with proper filtration), you can use sunspots to focus the image.
If no sunspots are visible on the surface of the Sun, use the solar limb (the edge of the Sun’s disk); it will be a bit trickier, but it works.
Focusing will be a lot easier if your telescope has a precision dual-speed focuser that locks into place.
Also, don’t forget to check focus from time to time as changes in temperature affect focus. For even more precise focus, think about getting a Bahtinov mask. Don’t forget to mark (with a sharpie) the focus position on the focuser of your telescope; you will spend less time focusing next time you’re out shooting the night sky.
If you need to use filters, you have two options. You can either use clip-in filters inside your camera or use screw-in filters as most T-adapters will allow you to do this.
If you shoot from a humid place the lens of your telescope will fog out after a while. Investing (or even building; it’s quite easy) in a dew heater will allow you to shoot all night long without thinking about dew forming on your lens.
As you are shooting at long focal lengths, vibrations will be a bit of a nuisance when shooting through a telescope. Use the mirror lock-up function in your camera at the start of the exposure, if shooting with a DSLR.
Mirrorless cameras will not be affected by vibrations as they don’t have a moving mirror inside. When you use mirror lock-up, you need to press the shutter button twice to take a photo. On the first press, the mirror will go up and lock into place. When you press the shutter button again, the shutter will open.
This is a very brief article on a very vast topic. It’s a start but you will learn a lot more as you practice. You will fail, and you will even be filled with frustration, but don’t stop. It will only get easier!