Focal Length (FL): The focal length of the telescope, usually in millimeter (mm).
Aperture: The diameter of the telescope opening often in inches or millimeter.
Lens: Did you ever wonder what made a low-end refractor telescope look so bad. It is the lens which for astrophotography they are made of glass. The better the glass, the lest light absorption and less scattering.
Lens or lenses: Hopefully more than one. The other thing that makes or breaks a refractor telescope is the number of lenses. A single lens will create a chromatic aberration. Light of different colors (frequencies) bend at different angles (speeds) so the different colors focus on different locations which will cause a purple haze around objects (chromatic aberration). This is bad for not just astrophotography, but for observational. Good telescopes will not only have good lens (good glass), but have two to multiple lens.
This is a Petzval design (our Takahashi on top of the Borr telescope has this design) with four lens and provides outstanding images. Other telescopes might have two or three lens design that provide excellent images. Known as doublets and triplets they may require correction add-ons or post processing to remove affects, but these are excellent designs.
The above telescope is not a refractor, but a reflector. It does have a correction plate to fix a problem that reflectors have, but since the light bounces off the mirror as apposed to going through a lens, it doesn’t suffer from the same chromatic aberration.
Finder Scope: The finder scope has a greater field of view than the telescope has and aides in finding objects. It needs to be aligned to the main scope.
Guide Scope: Often guiding is done with a guide scope which is often a finder scope with a camera mounted on it.
Off axis guiding (OAG): With the Astro rig above it is using OAG. The OAG device places a small 45-degree mirror in the light path of the main telescope which is captured by the guide camera. This removes the need for a separate guide scope, but is more complicated to set up.
Main Camera: Are generally broken down into two categories. Deep sky objects (DSO) and planetary. DSO tend to have larger sensors and cooled. Planetary tend to be much smaller, usually 1-2 mega-pixel and are not cooled.
Planetary vs DSO: When imaging planets most techniques do not require long exposures, so no cooling is required and the planet is tiny and bright so big sensors are a waste. This makes for a less expensive camera. DSO are larger and tend to be very dim. Techniques for imaging DSO usually require multiple long exposures to capture as much light as possible. This will cause the camera sensor to heat up and can create noise in the image. Cooling the camera (often using thermal electric cooling (TEC)) cuts down on that noise significantly.
Above: Dobsonian Telescope
DSLR or Full Frame Handheld cameras: These are often the first cameras people use to Astro image as they may already have one on hand. Many companies make adapters to connect camera bodies to telescopes. Although the above rig might seem complicated, some astro-imagers' first experiences with imaging were with a Dobsonian with a DSLR connected to it.
Controller: A controller is a computerized device that is connected to the cameras, the mount and automated devices that sends commands to the camera, mount and devices during a capture session. It can be a IOT device like you see above or a computer, mounted with the scope or just connected or can be as simple as a intervalometer to control just the camera. It also stores the images taken and can even stack (we’ll get to that) images.
Mount: Although not all astro-imagers start with this, it is the main component to a good astrophotography rig. A steady mount with good tracking is key to capturing images of a thing millions of light years away.
Power supply: When imaging can be done close to a power outlet, you should use it; but when you are more remote, or you don’t want to dangle a cord to the building a good power supply can run your rig. Most have 12-volt outlets along with USB and 110-volt AC. Most mounts and equipment run off of 12 volts systems.
