Plate solving is software that looks at a photo of the night sky, identifies the star pattern by matching it to a catalogue, and works out exactly where your telescope is pointing — to the arcsecond. Your software then nudges the mount until your target sits precisely where you want it, so you can centre and frame any object, even one far too faint to see.
Plate solving is the quiet superpower of modern astrophotography, and it is really astrometry put to practical use, measuring exactly where your telescope is pointing. It turns “hunting blindly for a smudge you can’t see” into “type the name, press go, and it’s centred.” Combined with good framing, it is what lets beginners reliably capture specific deep-sky targets. This guide explains what plate solving is, how it works, the best free tools in 2026, and how to use it to frame your shots like a pro.
What this guide covers
- The problem: finding what you can’t see
- What is plate solving?
- Plate solving vs go-to alignment
- The best plate solving tools
- How to centre a target with plate solving
- Framing your target
- Common plate solving problems
- Frequently asked questions
The problem: finding what you can’t see
Most deep-sky targets are invisible in a short exposure. A faint galaxy might need several minutes of stacked light before it even appears, so you cannot simply look at the screen and centre it. Worse, a go-to mount that is a degree or two off will happily place your target near the edge of frame — or just outside it — and you will not know until you have wasted twenty minutes imaging empty sky.
Plate solving removes the guesswork entirely. Instead of trusting the mount’s idea of where it is pointing, it photographs the actual sky and reads the truth from the stars themselves.
What is plate solving?
Plate solving is a form of astrometry — the precise measurement of star positions. The software detects the stars in your image, measures the geometric pattern they form, and searches a catalogue for the one patch of sky that matches. Once it finds the match, it knows the exact coordinates, scale, and rotation of your frame.
The clever part is that it works from the star pattern alone — no go-to alignment, no knowing where you started. Give it any photo of stars and it can tell you where that photo points, which is why it is sometimes called a “blind solve.”
Plate solving vs go-to alignment
A traditional go-to alignment teaches the mount where it is by having you centre two or three named stars. It works, but it is only as accurate as your centring and it drifts as the night goes on. Plate solving is fundamentally better: every solve is an absolute, independent fix on the real sky, accurate to arcseconds, with no star-centring chore.
In practice the two combine. Many imagers do a rough go-to, then let plate solving take over to refine the pointing and centre the target perfectly. Modern controllers do this automatically — you choose a target and the software slews, solves, corrects, and re-solves until the object is dead centre.
The best plate solving tools
- ASTAP. Free, fast, and the go-to local solver for many capture programs; works entirely offline once you download a star database.
- Astrometry.net. The well-known engine that can blind-solve almost anything, available online or installed locally.
- ASIAIR. ZWO’s controller has plate solving built in — pick a target and it centres it with no PC.
- N.I.N.A. Free Windows capture software with excellent plate-solve-and-centre and framing tools.
- SharpCap and PlateSolve2. Popular solvers that integrate with many imaging workflows.
For a beginner, the solver is usually bundled with whatever capture software or controller you already use, so you rarely choose in isolation. The key point: almost every one of these is free, and a local solver like ASTAP works without internet in the field.
How to centre a target with plate solving
- Pick your target in the capture software and send a go-to slew to get roughly close.
- The software takes a short exposure and plate-solves it to learn where you actually are.
- It compares that to your target’s coordinates and calculates the error.
- It slews to correct, then solves again to confirm.
- After one or two cycles, the target is centred to within a few pixels.
The whole sequence takes under a minute and is repeatable to the pixel, which matters when you return to the same target across several nights and need every panel to line up.
Framing your target
Centring is only half the job — framing is the creative half. Framing means deciding how a target sits in your field of view: where you place it, how you rotate the camera, and whether two objects can share one frame. A galaxy pair or a wide nebula complex rewards careful composition just like any photograph.
Before you go outside, plan the shot. Our telescope field of view simulator overlays your exact camera-and-scope frame on any target so you can see whether it fits and at what rotation it looks best. Knowing your image scale also tells you how large the target will appear in pixels. Plate solving with a defined rotation angle then reproduces that planned framing on the sky automatically.
Blind solve vs hinted solve
There are two ways a solver can work. A blind solve is given nothing — no idea where the scope points or what scale the image is — and searches the whole sky for a match. It always works eventually but can be slow. A hinted solve is told roughly where you are pointing and your approximate image scale, so it only checks that small region and matches almost instantly.
For night-to-night imaging you almost always use hinted solves, because your capture software already knows your focal length, pixel size, and rough pointing. Keep a blind solver like Astrometry.net in reserve for the rare case when your mount has lost its position entirely — point anywhere, blind-solve, and you instantly know where you are again. Entering the correct pixel scale is the single biggest factor in fast, reliable solves.
Plate solving beyond centring: flips and alignment
Centring a target is only the first use of plate solving. The same technology powers two other jobs that used to be fiddly. The first is the meridian flip: when a target crosses the meridian, a German equatorial mount must swap sides, which leaves the target re-framed slightly differently. Plate solving re-centres it perfectly after the flip, so your panels still align and the run continues unattended.
The second is polar alignment. Routines like the one in N.I.N.A. use a sequence of plate solves to measure how far your mount’s axis is from the pole and guide you to correct it — no view of Polaris required. If you have read our polar alignment guide, this is the plate-solve method in action. One technology quietly underpins centring, flips, and alignment alike.
Camera rotation and matching past sessions
Plate solving also reads your camera’s rotation angle, which matters in two ways. When planning, it lets you set a deliberate composition — tilting the camera so an elongated galaxy runs diagonally, or so two objects both fit. When returning to a target across several nights, it lets you reproduce the exact same rotation so every night’s data stacks cleanly without cropping away the edges.
Many imagers note the solved rotation angle from a good night and dial the camera to match it next time. Software with a framing assistant makes this visual: you rotate the overlay on screen, and it tells you the exact angle to set on the sky.
Shooting mosaics of large targets
Some targets are simply too big for one frame — the Andromeda Galaxy, the Veil Nebula, or a sweeping region of the Milky Way. The answer is a mosaic: several overlapping frames stitched into one large image. Mosaics are only practical because of plate solving, which places each panel at precisely the right coordinates so the overlaps line up for stitching software.
Plan a mosaic the same way you plan a single shot — work out how many panels your target needs with the field of view simulator, leave a generous overlap, and let your capture software solve and centre each panel in turn. It is an advanced move, but plate solving makes it achievable even for a patient beginner.
Common plate solving problems
- It won’t solve. Usually too few stars (exposure too short), bad focus, or the wrong pixel scale entered — give the solver a correct focal length and pixel size.
- Wrong scale hint. If you tell the solver the wrong image scale it can fail or solve slowly; a correct hint makes solves near-instant.
- Clouds or trailing. A trailed or cloud-fogged frame has no clean star pattern to match.
- No internet for an online solver. Install a local solver like ASTAP so you are never dependent on a connection in the field.
- Solves but won’t centre. Check the mount is connected for pointing corrections, not just the camera.
From star-hopping to plate solving
Before plate solving, finding a faint target meant “star-hopping” — manually nudging the scope from one recognisable star to the next using a chart, hop by hop, until you arrived in the right neighbourhood. It is a genuine skill and still worth learning for visual observing, but for imaging it is slow, error-prone, and nearly impossible for objects too dim to see in the eyepiece.
Plate solving replaced that hunt with certainty. Instead of guessing whether the smudge in your frame is the right galaxy, the software tells you precisely what you are looking at and how far you are from where you want to be. For a beginner, this is the difference between a frustrating night of fruitless searching and a productive one spent actually collecting data on a centred, well-framed target.
That certainty also makes your time efficient. A single solve confirms your pointing, your scale, and your rotation in one short exposure, so you spend the clear hours imaging rather than troubleshooting where the scope is aimed.
Frequently asked questions
Is plate solving necessary for astrophotography?
It is not strictly required, but it is so much faster and more accurate than manual star-hopping that almost every deep-sky imager uses it. For faint targets you cannot see, it is close to essential.
What is the best free plate solving software?
ASTAP is the most popular free local solver because it is fast and works offline. Astrometry.net is excellent for blind solving, and N.I.N.A. bundles plate solving with strong framing tools at no cost.
Does plate solving replace polar alignment?
No. Plate solving tells you where you are pointing, but you still need good polar alignment for tracking. In fact, some software uses plate solving to help you polar align faster.
How long does a plate solve take?
With a correct scale hint and a local solver, usually one to a few seconds. A blind solve with no hints can take longer but still finishes in well under a minute on modern hardware.
Why does my plate solve keep failing?
The usual causes are too few stars from a short or out-of-focus exposure, or an incorrect pixel scale. Lengthen the exposure slightly, confirm focus, and enter the correct focal length and pixel size.
Can you plate solve with a DSLR?
Yes. Plate solving works with any camera that produces a star image, including a DSLR or mirrorless camera. As long as the frame shows enough stars and you give the solver your focal length and pixel size, it solves just as well as a dedicated astronomy camera.
Next steps
Plate solving and framing are the last setup skills before you are imaging targets with intent rather than luck. With polar alignment, focus, and autoguiding all dialled in, you have the complete beginner workflow. See how it all fits together in our essential astrophotography fundamentals guide, and plan your next target in the field of view simulator.
Written by Hamza Touhami, an astrophotographer since 2008 who operates a remote imaging rig under the dark skies of Deepsky Chile.
