Quick Start Guide Part 1 for Beginner Digital Astrophotography
If you have a digital camera and want to try your hand at astrophotography, but don’t really know where to start, you’ve come to the right place!
I’ll try to give you a little bit of basic information here on these Quick Start web pages to get you started. You’ll find more on the rest of the web, and in any number of books if you really want to learn all about it.
You can get started taking astronomical pictures with almost any kind of camera. You’ll be able to shoot beautiful twilight pictures of the Moon and planets and constellations with just a camera on a tripod.
If you have a telescope, you’ll also be able to shoot the Moon, and even close-ups of craters on the Moon.
To shoot deep-sky objects like galaxies and nebulae, you will need a telescope on an equatorial mount to track the stars so you can use the long exposures required for these faint objects. You can use a computerised Alt-Azimuth mount to shoot brighter deep-sky objects, but you really need something like a German Equatorial mounting with motor drives on both axes to do any kind of serious long-exposure deep-sky astrophotography.
You can get started taking simple astrophotos with almost any kind of digital camera. A tripod helps, but you don’t really even need one of those.
First lets go over some quick facts and terms about digital cameras.
Shutter Speeds, Aperture, ISO
Except for the moon, the stuff we want to shoot in the night sky is pretty faint. That means we need to record as much light as we can. Cameras control the amount of light taken in a picture by two basic ways. There is a shutter that opens and lets light hit the digital sensor in the camera, and there is a variable-sized hole, called the aperture or diaphragm, in the camera lens. If we leave the shutter open longer, we record more light. If we use a larger hole, we let more light in. Nothing complicated here.
Shutter speeds run in fractions of a second, usually around 1/1,000th of a second at the shortest exposure to many seconds at the longest. Most DSLRs also have a setting called “bulb” that keeps the shutter open as long as you press the shutter button down.
Aperture settings run in a crazy series of numbers like f/2.8, f/4, f/5.6, and f/8. Confusingly, the smaller the number, the larger the hole in the diaphragm. So, f/4 is a bigger hole than f/8.
Most cameras also have a way to change their “sensitivity“. This is kind of a trick setting though. You can’t really change the sensitivity of the sensor in the camera, but you can adjust a setting called the ISO, which is sort of like a multiplier factor. ISO settings may run from 100 to 400 in simple cameras, or up to 800, 1600 or 3200 or higher in more expensive cameras. The higher the ISO number, the brighter the resulting image will be if you keep the shutter speed fixed. Unfortunately, the electronic noise gets worse at the higher ISO settings, but we won’t worry about that for now.
To get started, you will have to figure out how to get your camera to use as long a shutter speed as possible, at as wide an aperture as possible, and at as high an ISO (that doesn’t generate too much noise) as you can. Unfortunately, you may have to read the manual to learn how to do this. Sorry. Your other option is to just dig around in the camera’s menus looking for these settings, but sometimes they can be hard to find and not labelled very clearly.
Set the camera on manual exposure if it has that setting. Then set the lens to its widest opening, usually f/2.8. Set the ISO to the optimum setting, usually 400 for simple point and shoot cameras. If the camera doesn’t have a manual exposure setting, set it to night mode.
The next thing you will have to worry about is the focus. Once again, dig through the camera manual, or menus, and see if you can figure out how to turn off the autofocus, and manually focus the camera on infinity (the farthest away that the camera will focus).
For more sophisticated digital cameras like DSLRs, you can pre-focus the camera in the daytime on something very far away, and then turn the auto-focus off. If you have a DSLR with a lens that you can manually focus, focus it on infinity and tape it down. Beware, many of these lenses actually will go past infinity, so you can’t just trust the markings on the lens.
Experiment with this in the daytime. If you have a point and shoot camera, it may have a setting for shooting at infinity and may have some type of icon of mountains to indicate this. Try shooting something very far away to be sure the setting works.
Many cameras also allow the white balance to be selected by the user. Once again, this setting will usually be buried in a menu somewhere.
Most will be set to auto white balance by default. This usually doesn’t give great results for nighttime photography, especially if you are shooting anywhere that has light pollution. This will usually make the sky a brown/red colour. A “Daylight” or “Sunny” white balance will accurately record the true colour of the sky, which under light pollution is usually brown/red. You might not be able to see this colour visually, but this is the sky’s real colour.
To get the pleasing colour for the sky, you can do one of two things:
Set a custom white balance on the sky itself before you take your pictures. Read the manual to learn how to do this! Note that you should only do this for dark night skies, not for sunsets or twilight colours. Also note that if you are only shooting JPEG file format in the camera, you really should use this method.
Set a custom white balance on the sky background when you open your raw file in Photoshop, or your camera manufacturer’s image processing program.
- Canon supplies Digital Photo Professional for free with your camera. Nikon supplies Nikon NX-D for free with your camera.
- Try them!
Take the Picture
- Shoot Raw file format.
- Set the camera to manual exposure mode.
- Set camera lens to widest aperture (f/2.8 is better than f/4 or f/5.6).
- Set the shutter to the 5 seconds.
- Set the ISO to 800 or 1600.
- Set the White Balance to Daylight or Sunny or use a Custom White Balance.
- Focus on infinity and lock the focus there.
- Use the self-timer or a remote release to open the shutter.
- Try different exposures.
Just put the camera on a tripod and aim it at a nice constellation and take the longest exposure at the widest aperture that you can, at ISO 800 or 1600 that you can. Heck, you don’t really even need a tripod. Just use a beanbag and place it on a solid object, like the hood of your car.
Use the camera’s self timer to open the shutter, and try not to move the camera during the exposure.
Take a series of exposures, and double the exposure for each. Start at 1 second, then try 2 seconds, 4 seconds, 8 seconds, 15 seconds and 30 seconds. Now you can examine the results on the back of the camera. See how easy that was!
Evaluate Your Images
Transfer the images from your camera to your computer.
The longer exposures will naturally record the most stars, but after a while when they get too long, the stars will start to trail. Really long star trails can make interesting photos in themselves and we will cover this in a later post. Look through your series of different exposures and pick the frame that is the longest without unacceptable trailing.
If you have even some software like Photoshop, Photoshop Elements or GIMP, you can adjust and tweak the colour balance to make the image more aesthetically pleasing. You can also adjust the brightness, contrast and colour saturation with these programs.
In-camera noise reduction is also offered in some cameras. This works by taking a “dark frame” (an exposure of the same length as your picture, but with no light reaching the sensor) and subtracting it from the image. This removes some of the thermal signal that looks like noise in long exposures. Just note that it will take twice as long to take a picture, so don’t freak out when the shutter closes after the exposure you have set, and you can’t take another picture immediately!
Turn off in-camera sharpening if your are shooting at high ISO and high ambient temperatures and long exposures.
The Next Levels
Taking your astrophotography to the next level usually means putting your camera on a telescope with a motorised mounting that is tracking the stars. You can put your camera with a lens on it riding “piggyback” of top of the scope. Or, if you have a DSLR, you can take the lens off the camera and hook it up to a telescope and use the scope as a camera lens.
If you only have a scope with an alt azimuth mounting to track the stars and compensate for the Earth’s rotation, then you will be limited to exposures of about 30 seconds maximum. Any exposures longer than this will suffer from “field rotation“, in which the stars rotate around the centre of the frame.
To shoot exposures longer than this, you really will need an equatorial mounting that is correctly polar aligned.
For really advanced astrophotography, you can shoot Raw file-format images and also shoot separate dark, flat-field and bias frames that you can use to calibrate your light images and greatly improve them.
We’ll talk more about these subjects in subsequent posts.