The author captured the Rosette Nebula under Bortle 2 skies with a ZWO ASI2600MC Pro camera on an Astro-Tech 72ED refractor on an iOptron CEM40 mount. This image includes 104 three-minute exposures. Credit: Molly Wakeling
Getting into astrophotography can be daunting. With so many different telescopes, cameras and mounts and all their variations, where to start?
The first piece of equipment to choose is the mount, the mechanical base to which the telescope is connected. For astrophotography, the mount must be motorized and ideally computer controllable. It might seem absurd, but the quality of the mount is more important than the quality of the telescope! Even the best quadruplet refractor will not produce good images if the stars are streaked by poor tracking.
While it is possible to perform astrophotography on an altitude-azimuth (alt-az) mount, they are limited; an equatorial mount will serve you much better. Equatorial mounts are aligned with the celestial pole so that only the right ascension axis follows the sky, while the declination axis is used only for small corrections. To get the best use out of a mount, it should be able to communicate with a computer, usually via USB, so that software can command it where to rotate and send fine-tuning commands using a process called autoguiding.
Expect to spend at least $2,000 on a mount with a reasonable load capacity: I recommend at least 25 pounds (11.3 kilograms) for use with small refractors. Don’t forget the weight of other gear you may possibly use, such as the camera, focuser, filter wheel, and guide scope, as well as the dovetail and rings or clamps you use to secure the scope.
Nowadays, the listed payload capacity of many mounts matches its true capacity for astrophotography; For some manufacturers and older mounts the rule of thumb of using 50% capacity for astrophotography applies. Almost all capacities listed by manufacturers take counterweights into account, so don’t worry about adding them to your weight calculation.
In my opinion, the iOptron CEM40 is a great place to start if you want to get serious about astrophotography. It is small and lightweight with a load capacity of 40 pounds (18 kg) and has excellent long exposure tracking when used with an autoguider.
Now we come to the telescope itself. I highly recommend starting with a small refractor, with an aperture between 60mm and 90mm. Their short focal lengths (400–700 mm) and relatively fast focal ratios (f/5 or f/6) make them very tolerant to tracking errors. This means you can start photography without the complication of autoguiding, while still gathering enough light to create a beautiful image. Refractors vary greatly in quality and price; you can do quite well with some doublets but you will get less chromatic aberration (blue halo around stars) with a triplet or apochromatic telescope. I was impressed with the Astro-Tech AT72ED I purchased last year from a friend (the newer AT72EDII retails for $519), and many people I know love their William Optics refractors; their Zenithstar apochromatic line ranges from about $600 to $1,000.
Finally, the camera. For the beginning astrophotographer, a one-shot color camera (OSC) is the way to go. You can also just start with a DSLR, preferably a mid-range computer-controlled one, but you’ll get better results and have more functionality with a cooled astrophotography camera. Although monochrome cameras provide images with higher resolution and signal-to-noise ratio, the additional complication and cost of four filters (luminance, red, green, and blue) and a filter wheel, as well as the additional image processing required , make them a difficult place to start.
A cooled OSC camera will provide excellent images and can be used with both multi-narrowband filters and light pollution filters, which are especially useful when taking images from the city. I love my ZWO ASI2600MC Pro ($1,499), and I’ve also gotten nice images from my ZWO ASI294MC Pro ($999). Be sure to use a luminance filter or UV/IR filter with an OSC camera on a refractor to avoid UV/IR halos.
Ultimately, start with everything you already own and know how to use. I took my first astronomical images with an 8 inch f/10 Schmidt-Cassegrain on an alt-az mount with a DSLR, which is the hardest possible starting point! But a high-quality equatorial tracking mount, a small refractor, and an OSC camera are a great way to get into astrophotography.
