Explainer
Charlotte Daniels introduces them and recommends the most suitable types of imaging
Astrophotography has become increasingly popular and thanks to modern technology, these days we don’t need enormous budgets to get great images; even smartphone cameras can give impressive results. The main consideration when selecting your astro camera is whether you wish to pursue wide-field, planetary, or deep-sky imaging. Typically, any device used for night-sky imaging will need to perform long exposures, have remote shutter capability and ISO control (to alter sensitivity to light).
Here we’re going to run through the most popular cameras for astro imaging, pointing out strengths and considerations. We begin with a type of camera that many people will have with them most of the time.
1 Smartphones
Many smartphones can perform entry-level astrophotography, while some offer the ability to take long exposures, meaning you can pick up Milky Way details or star trails. You can also hold smartphones up to a telescope eyepiece to take pictures, or use a smartphone adaptor (see boxout, right). This enables lunar and planetary imaging, but it’s difficult to get sharp images. Although some smartphones have multiple cameras installed, these are tricky to line up to eyepieces. In a nutshell, smartphones are not dedicated astrophotography products and don’t offer the exposure control of a DSLR camera.
Best suited for: Star trails, Milky Way and general wide-field imaging
Limitations: Deep-sky photography
Accessories: Tripod; telescope adaptor
2 DSLRs
DSLRs (Digital single-lens reflex cameras) are good all-rounders. Because you can alter the ISO level and manage exposure lengths, these cameras are easily adapted for many astronomy targets. Increasing the ISO setting ensures a DSLR can pick up details from deep-sky objects, including nebulae, but if this is coupled with a long exposure time there can be an issue with noise (unwanted artefacts) creeping in, which can be because the ISO is too high (the best ISO varies between cameras) or because the exposure time is causing the sensor to warm up.
DSLRs with ‘Live View’ or video capability can be used for planetary imaging, although they’re less efficient at cutting through atmospheric distortion than a planetary camera.
Some astro imagers modify a DSLR by removing the infrared (IR) filter, which makes it more sensitive to nebulae. A modified DSLR also allows narrowband filters to be used, which improve image details.
Best suited for: Wide-field, lunar and deep-sky imaging
Limitations: Exposures lasting over ~5 minutes, planetary imaging
Accessories: Tracking mount; intervalometer (remote shutter release cable)
3 Planetary cameras & webcams
Planetary imaging requires a telescope and you’ll find that reflectors are most suitable because of their long focal lengths. If a planetary camera is also coupled with a 2x Barlow lens you’ll be able to achieve the magnification required for planetary detail, while the camera’s high frame rate will allow you to cut through atmospheric turbulence.
You’ll require a laptop to run these cameras and, as you’re viewing an object up close, a solid tracking mount is also needed, which allows you to keep the planet central in the field of view. When it comes to deep-sky imaging, planetary cameras have small sensors which means they’re not always suited.
It’s also possible to modify an off-the-shelf webcam for planetary imaging, so that it fits into the eyepiece holder of your telescope (see the box below for more details).
Best suited for: Lunar and planetary imaging Limitations: Deep-sky objects and wide-field imaging Accessories: Laptop; 2x Barlow lens; processing software (eg RegiStax)
4 CMOS & CCD cameras
CMOS and CCDs are ‘dedicated astrocams’, which are designed to be fitted to a telescope. Each comes in ‘colour’ – for RGB (Red, Green and Blue) imaging
– or ‘mono’ variants. Mono cameras require the use of colour or narrowband filters.
CCD (charge-coupled device) cameras are suited for long-exposure photography (10-plus minutes per frame) because they have ‘set-point’ cooling systems that keep the sensor temperature constant, which is known as ‘active’ cooling. CMOS sensors perform better with shorter exposures and come as either actively or ‘passively’ cooled.
Laptops are needed to run either device. To maximise CCD exposure times, additional accessories – including guiding equipment and software – are often required. Using these cameras can be a steep learning curve, so it’s best to build up to it gradually.
There are adaptors available that fit these ‘astro cams’ to DSLR camera lenses, which allows you to use them for wide-field deep-sky imaging.
Best suited for: Deep-sky imaging
Limitations: Milky Way and wide-field imaging Accessories: Laptop; telescope; guide equipment and software