How to build an astrophotography rig: choosing parts that work together

4 November 2026 · 9 min read

An astrophotography rig is a chain. The telescope decides which cameras suit it, the camera and corrector decide the spacers, everything together decides the mount, and the mount decides how you guide and power it. Choose the parts in the wrong order and something always ends up not fitting: a camera that can't reach focus, a mount at its limit, a filter wheel that won't work with your controller.

This guide goes through the parts in the order that avoids those problems, with the rule of thumb for each one. If you'd rather start from a working example, see the best beginner astrophotography setup.

The parts of an imaging rig

Step 1: Decide what you want to photograph

Everything starts with field of view. Big nebulae and Andromeda span degrees of sky; most galaxies are a few arcminutes across. No single focal length suits both.

Your field of view in degrees is roughly 57.3 × sensor width (mm) ÷ focal length (mm). An APS-C sensor (23.5 mm wide) at 400 mm covers about 3.4°. How to calculate your telescope's field of view has worked examples, and the Targets tab previews any of 520 objects in your own field.

Rule of thumb for a first rig: 250–450 mm covers the most famous targets and is the easiest focal length to track.

Step 2: Choose the telescope

For deep-sky imaging, three things matter more than aperture:

• Focal length, from step 1.
• A flat field. Stars stay round to the corners only with a flattener or a design that has one built in. Many small astrographs (Askar SQA and FRA, William Optics RedCat and Cat, Celestron RASA) include one, which saves a whole step.
• f-ratio. Lower is faster. At f/4 you collect a given signal in about half the time it takes at f/5.6. Faster scopes are less tolerant of focus and tilt errors.

Small apochromatic refractors are the usual first choice: no collimation, quick to cool down, and sharp colour correction. Newtonian astrographs give more aperture for the money but need collimation. Schmidt-Cassegrains suit small targets and planets; at 1500–2800 mm they need a heavy mount and an off-axis guider. Choosing a first telescope for astrophotography compares them in detail.

Also check the telescope's image circle: the size of the well-corrected area at the focal plane. A full-frame sensor needs about 44 mm; APS-C needs about 28 mm.

Step 3: Choose the camera

Three numbers decide whether a camera suits a telescope.

Sensor size against the field you want and the scope's image circle. A bigger sensor gives a wider field at the same focal length, but needs bigger filters and a bigger image circle.

Pixel size against focal length and seeing. Image scale in arcseconds per pixel is:

206.265 × pixel size (µm) ÷ focal length (mm)

On a typical night the atmosphere blurs stars to 2–3″. Aim for an image scale about a third to a half of your seeing: roughly 0.8–1.5″/px for most backyards. Wide-field rigs are usually undersampled (2–4″/px), which is normal and fixed well by dithering and drizzle. Long focal lengths are often oversampled; binning 2×2 fixes that. See Image scale and sampling.

Colour or mono, cooled or not. A one-shot-colour (OSC) camera is simpler and suits a first rig. A mono camera with filters is more sensitive and better for narrowband but needs a filter wheel and more nights per target. Cooling cuts thermal noise and makes dark frames reusable. DSLR, mirrorless or astro camera? goes through the choice.

Step 4: Work out the corrector and back focus

Most flatteners and reducers need the camera's sensor at an exact distance behind them, usually 55 mm, to within about a millimetre. Everything between them counts: adapters, the filter wheel or drawer, an off-axis guider, the camera's own flange distance, plus about a third of the thickness of any filter glass in the light path.

Add up the train, subtract it from the required back focus, and the difference is the spacers you need. If the answer is negative, the train is too long, and you'll have to remove something (often the off-axis guider or a bulky filter wheel). Back focus explained walks through it with examples, and the rig builder does the sum and suggests standard spacer sizes.

DSLRs need a T-ring that brings them to the 55 mm standard. Dedicated astro cameras usually come with spacers to reach it.

Step 5: Choose a mount that has room to spare

Add up everything the mount carries: telescope, rings and dovetail, camera, filter wheel, guide scope and camera, focuser motor, dew heaters, controller and cables. Then compare it with the mount's imaging limit, not the number on the box:

• Worm-gear equatorial mounts: about 50–60% of the rated payload.
• Strain-wave mounts: up to about 80%, but plan on guiding.
• Star trackers: about 70%, and short focal lengths only.

Long focal lengths need more margin than short ones, because every error is magnified. See How much can your mount really carry? and Star tracker or equatorial mount?.

Step 6: Pick filters, and something to hold them

Most beginners need no filter, or one: a UV/IR cut for a modified DSLR or some colour cameras, or a dual-band (Hα and OIII) filter for emission nebulae from a light-polluted sky. Mono cameras need a set of filters and a wheel. See Dual-band vs narrowband filters.

Then check the size. At a given f-ratio, a bigger sensor needs bigger filters, or the corners vignette:

• 1.25″ filters suit small sensors (up to about 4/3).
• 36 mm unmounted filters suit APS-C.
• 2″ or 50 mm filters suit full frame.

A filter drawer holds one filter and adds little to the back focus. A filter wheel holds five to eight but adds 15–25 mm, which has to fit within the back focus from step 4.

Step 7: Decide on guiding

Unguided, most mounts manage a minute or two at short focal lengths. Autoguiding uses a second small camera to watch a star and correct the mount many times a minute, which makes five- to ten-minute subs routine.

• Guide scope: a small 30–60 mm scope on top of the main one. Simple, and right for focal lengths up to about 800 mm.
• Off-axis guider (OAG): a small prism inside the imaging train. Best for long focal lengths and SCTs, but it uses back focus.

What matters is the guiding ratio: guide-camera image scale ÷ imaging scale. Up to about 4× is comfortable. See Guide scope or off-axis guider?. Beyond about 300 mm, plan on guiding from the start.

Step 8: Choose something to run it all

A modern rig is run by a computer: it controls the camera, focuser, filter wheel and mount, plate-solves to frame the target, guides, dithers and saves the files.

• Laptop running N.I.N.A., SharpCap or APT. Flexible, but power-hungry and vulnerable to dew.
• Mini PC on the mount, controlled from a laptop or tablet over Wi-Fi. The usual N.I.N.A. setup.
• Raspberry Pi running KStars/Ekos (for example via Astroberry or StellarMate). Cheap and frugal with power.
• Dedicated controllers such as the ZWO ASIAIR. Easiest to set up, but the ASIAIR only drives ZWO cameras and focusers (plus some Canon and Nikon DSLRs).

Check that your choice supports every camera, the mount and the filter wheel before buying them. This is one of the most common surprises.

Step 9: Plan power and dew

Add up the average draw of the camera's cooler, the mount, the controller and dew heaters, then compare it with your battery's usable watt-hours. A cooled camera and two dew heaters can draw 30–50 W on a cold night, which empties a small power station before dawn. See Powering your rig in the field and How to stop dew ruining your night.

An example, step by step

Say you live in a suburb (Bortle 6), want the big winter and summer nebulae plus a few large galaxies, and need to carry the rig out of a garage.

1. Targets: M42, the Heart and Soul, North America, M31, M33. A field of 1.5–3° → 300–450 mm.
2. Telescope: a 72 mm f/5.6 astrograph with a built-in flattener, 400 mm, back focus 55 mm.
3. Camera: a cooled colour camera with a square 11 mm sensor and 3.76 µm pixels → 1.9″/px and a 1.6° square field. Slightly undersampled for 2.5″ seeing, which is fine.
4. Back focus: the camera's sensor sits about 17 mm behind its front thread, so about 38 mm of spacers, including a third of the filter's thickness.
5. Filters: a dual-band filter for nebulae from the suburbs, screwed into the flattener.
6. Mount: the rig weighs about 4.6 kg; a mount rated 12.7 kg gives a 7.6 kg imaging limit. Comfortable.
7. Guiding: a 32 mm guide scope with a small mono camera → ratio 2.4×. Good.
8. Control: a Raspberry Pi running Ekos, which supports the camera and mount.
9. Power: about 31 W average → around 18 hours on a 640 Wh LiFePO4 battery.

The full equipment checklist

The imaging train: telescope or lens · reducer or flattener (unless built in) · adapters and spacers · filters and a drawer or wheel · camera · T-ring for a DSLR.

Tracking: mount and tripod · counterweights · dovetail and rings · guide scope or OAG · guide camera.

Control: controller or laptop · USB cables and a powered hub · electronic focuser (optional, very useful) · capture, guiding and plate-solving software.

Power and comfort: battery or mains supply · power distribution box · dew heaters and controller · dew shield · red torch · warm clothes.

Small things that save nights: a Bahtinov mask for focusing · a flat panel or white T-shirt for flats · cable ties or a cable sleeve · spare USB cables · a compass or polar-alignment routine · a printed or offline checklist.

Common combinations that don't work

• A full-frame camera on a scope with a 30 mm image circle (dark, distorted corners).
• An off-axis guider plus a filter wheel behind a 55 mm corrector (no room left).
• 1.25″ filters in front of an APS-C sensor at f/4 (vignetting).
• An 8″ SCT on a mount rated for 10 kg (it can carry it, but it can't image with it).
• A dedicated controller that doesn't support your camera brand.
• A guide scope at 120 mm on a 2000 mm telescope (ratio around 8×).

The rig builder checks every one of these as you pick parts, and if something you own isn't in the catalog, you can add it as your own part with the numbers from its manual.