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DomeSynchronization.csNINA can slave your dome to your telescope, but only if it knows precisely where your mount sits relative to the dome's center. Getting those numbers right by hand is easy to get wrong. This tool converts either a physical measurement or values you already have into the exact signed fields NINA's Options → Dome tab expects, then shows you live whether your shutter will actually clear the OTA at any given pointing.
Save Setup / Load Setup exports everything as a JSON file, or restores it. Reset to Defaults reloads with every field back to its starting value. The status banner just below the title tells you at a glance whether the current pointing is valid: green for everything clears, amber for "pointing was adjusted," red for a real problem.
The same page rearranges rather than hiding anything. On a tablet the rail moves above the 3D view instead of beside it; on a phone everything becomes a single column and the measurement fields, the reasoning and the sky notes each drop to one column of their own.
Nothing is removed at any width, and there is no sideways scrolling — the page simply gets taller.
Drag the grip along the bottom edge of the 3D view — the chevrons above and below it show which way it moves, and it turns green while you are dragging to make it taller or shorter, trading height with the figures below it. Double-click the bar to go back to the default. With the bar focused, the arrow keys nudge it and Home resets it.
Whatever height you settle on is saved with your setup. On a phone the control is hidden, since the layout stacks and the page scrolls instead.
The five park positions Astro-Physics define are on the pointing bar as AP PARK 1–5. They are taken from Astro-Physics’ own published sheet, and three of them depend on your latitude, so they are computed rather than fixed.
Two points worth knowing. Astro-Physics describe Parks 2 and 3 as having the “RA axis vertical”, but a German equatorial’s counterweight shaft can only reach 90° minus your latitude below horizontal — 49.8° at latitude 40, and less further north. It is only truly vertical at the equator, and their photographs are taken at their own latitude. And Astro-Physics now consider Park 1 obsolete, recommending Park 4 in its place and Park 5 where the position must be accurately levelled.
The RA field is degrees of hour angle, zero on the meridian, positive to the west. Fifteen degrees is one hour. The slider is deliberately fine near the meridian and coarse towards the ends, so the crossing is easy to sit in.
Two checks you can make by eye: with the field at 0 and declination equal to your latitude the telescope should read altitude 90°, and with the field at 0 and declination 0 it should read due south at an altitude of 90° minus your latitude.
The pier side is not really a free choice. At a given hour angle only one side is reachable; the other puts the mount through the pole with the counterweight above the tube, which is not a pose a mount adopts. The side therefore follows the hour angle, and the change is animated so you can see which way the tube sweeps.
The chip at the top right shows the version and a four-character build stamp. The version says what changed; the stamp identifies the exact file, and changes whenever the file does. If you are reporting something, quote both.
Everything sits on one screen; there is nothing to scroll past.
The values NINA needs are the first thing in the rail and stay open, since they are usually what you came for. Copy puts them on the clipboard in the order NINA's own fields appear.
Every value can be clicked for a short explanation of what NINA does with it — worth reading once for the GEM axis in particular, which is measured to the optical axis you image through and so includes your rings.
If you already have working figures, tick I already have my NINA values. The three offsets, the dome radius and the GEM axis become editable, and the rest of the tool follows what you type. Formulas opens a note at the foot of the rail describing how each is derived.
"I'll measure my dome" — plumb-bob the dome's true center and the mount's RA/Dec intersection down to the floor, mark them, then measure heights and the straight-line N/S and E/W distance between the marks (true north, not magnetic).
"I already have my NINA values" — type in the signed values directly.
Dome radius (center to rim), shutter width (straight-line, not arc), rotator precision / Azimuth Tolerance, and wall height (affects 3D view only, not the NINA math).
GEM — GEM Axis Length, measured with the mount slewed 90° from the meridian. Alt/Az or Fork — Dec Horizontal Offset. Dual saddle reveals the Lateral Axis Length field and lets you choose which OTA NINA tracks.
A measured horizon profile is saved with the rest of your setup, not just the flat limit. Loading that file brings back the profile, the custom mode, and the name of the .hrz file it came from — so the status line tells you which horizon was restored rather than just how many points it found.
Flat minimum altitude, or a full custom profile loaded from a .hrz file (same format as Stellarium). Shown in the 3D view as a wireframe skyline.
Collapsed by default. Sweeps the entire sky for both pier sides side by side.
| 🟢 Green | Shutter clears |
| 🔴 Red | Vignettes or misses the dome |
| 🟤 Brown | Below your local horizon |
| ⚪ Grey | Mount geometry invalid there |
Below the plots, Why this coverage accounts for the sky you cannot reach. Your local horizon is reported first and set aside, since no dome recovers it. What remains is attributed either to the shutter — with the compass sectors and altitudes affected — or to the mount, where the optical axis misses the dome entirely.
If the aperture is wider than the slit, no pointing can clear and the panel says so. If the slit is wider and you are still losing sky, the cause is the aperture swinging off the dome centre line, and moving the mount toward the centre is the fix rather than a larger slit.
Enter the dome's diameter — rim to rim across the base, which is what manufacturers quote and what you can measure directly. The radius every calculation works from is shown immediately beneath it, so you can check the halving rather than take it on trust.
The Options → Dome panel is always in millimetres, whichever units you are working in, because that is what NINA's fields expect. Copy them across unaltered. Your measurement inputs still follow the unit toggle as normal.
This is your own limit, not an obstruction: how low you are willing to observe. It starts at 0, which applies no limit, so a pointing is only reported as blocked when the building or dome actually blocks it.
Raise it if you would rather not observe close to the ground, or switch to a measured horizon profile if terrain is the real constraint. Either way the tool will tell you which of the two is stopping you.
Beneath the status banner, a four-point summary explains why the setup does or does not hold together: the pointing model, the pier height, what your walls cost you at the horizon, and how far off centre the mount sits. Each line states the reason rather than just a verdict, and the heading takes the worst of the four. Every figure is one the tool has already computed elsewhere, so the summary and the detail cannot disagree.
The Mount System card judges your pier against the target the classic pier-height worksheets use: the declination axis level with the dome's centre height. At that height the volume your tube sweeps is concentric with the hemisphere, which is the condition that needs the smallest dome.
The verdict says how far off you are and which way, gives the pier height that would centre it, and states what the miss costs in dome radius. If the optics will not fit the dome at any pier height, it says that too.
The tube is usually balanced so its centre sits on the declination axis, but not always. OTA offset is the distance between the centre of the whole assembly — tube plus dew shield — and that axis, measured along the tube. Positive slides it toward the aperture, negative toward the focuser. Leave it at 0 if the assembly is balanced on the axis.
It drives how far the tube reaches when it swings, so an unbalanced tube is no longer assumed to be a typical one.
The Optical System card takes a dew shield length. It is added to the tube and drawn ahead of it in a lighter tone. It counts toward the swept reach, because a shield is the part most likely to catch a wall or a shutter edge. Leave it at 0 if you do not use one.
Some library mounts show only their declination-axis offset and counterweight shaft. For these, the manufacturer publishes the declination-axis height only as a figure that varies with latitude, which cannot be separated into the two constants this tool needs from a single reading. Selecting one of these leaves your mount head height untouched and says so, rather than filling it with a guess. Measure it, or take the manufacturer's figure at two different latitudes and solve for the pair.
The counterweight sweeps its own circle about the RA axis, and on a short optical tube it is the widest thing on the mount. Enter the distance from the RA axis to the far end of the shaft. Choosing a library mount fills this in from that mount's published shaft length; set it to 0 if you run a harmonic mount without a counterweight.
Whichever reaches further — telescope or counterweight — sets the swept radius, and the clearance line tells you which one it is.
What sweeps past a wall or a shutter edge is the widest part of the tube, which is normally the rings and dovetail rather than the tube itself. Enter that measurement as the OTA outer diameter. Left at 0 it is estimated at 1.3× the clear aperture, which suits a closed tube in rings but is only a guess. The 3D view draws the rings at whichever figure is in force, so if they look wrong against your tube, that is the cue to measure.
Rings matter a second time. They raise the tube above the saddle, so the optical axis sits further from the declination axis than the mount's own published figure. A library preset gives dimension C for the bare mount; measure C to the optical axis you actually image through and enter that instead.
If your mount is not in the list, or is listed without dimensions, measure it against the diagram, tick Use my own values, and press Save this mount. It is added to the list under Your mounts and stays there next time you open the tool.
Export my mounts writes them to a file you can keep or pass to someone else; Import mounts reads one back. Anyone who owns a mount the manufacturer does not publish figures for can measure it once and share it.
Show swept volume in the 3D view draws the space the telescope and counterweight sweep through as they turn. It is the shape the clearance figures describe, so you can see it against the walls or the dome shell rather than working from the numbers alone.
It draws blue when everything clears and red when something fouls the pier, matching the pier-strike line in the setup check.
Switching pier side rotates the mount through the pole: the tube and the counterweight change sides, and the tube rolls 180° about its own axis. It looks upside down because it is — that is what a German equatorial does, and it is why a meridian flip rotates your field of view and needs re-framing.
The pointing does not change. What does change is the required dome azimuth, because the optical axis sits off the dome centre: the same target needs the shutter in a different place depending on which side the telescope is on. That difference is the reason this tool exists.
The setup check reports whether the counterweight clears the pier as the mount turns, and by how much. A margin under about six inches is flagged as worth confirming on the real thing. On a harmonic mount, which carries no counterweight, the same line reports the back of the tube instead — that is what comes closest to the pier on those.
The list is grouped by how much is actually known about each mount, because more mounts are named than dimensioned:
A partial entry fills in what is known and deliberately leaves the rest alone rather than inventing a figure. If your mount is in one of the lower groups, measure it and enter the figures under Use my own values; the tool then treats it exactly like a full entry.
Setups and exported horizon files carry the date and time they were saved — dome-geometry-setup_2026-07-28_1432.json. Year first, so a folder of them sorts into order by name, and local time so the stamp matches the clock you were looking at.
The solid wall below the springline blocks low pointings, exactly as the walls of a roll-off roof do. Wall height, floor to springline therefore affects clearance and not just the preview.
If the wall top sits below your optical axis it takes no sky at all. If it rises above, the tool reports the altitude it cuts you off at and says plainly that it is the wall rather than the shutter opening standing in the way — a lower wall, or a taller pier, buys back the difference.
The Mount System card carries a small library of common mounts. Choosing one fills in its geometry — the mount head height and, for an equatorial, the declination-axis offset — and switches the mount type to match. Generic is the default and changes nothing, so measured values are never overwritten unless you ask for a preset.
An equatorial's declination axis sits at A + B × sin(latitude) above the pier flange, since dimension B runs along the polar axis. Presets re-apply when you change latitude so the figure stays right for your site.
Preset dimensions are community measurements, not manufacturer specifications, and every field they fill remains editable. Where sources disagree the card says so. Measure your own mount before building to tight clearances.
Select Measure my own and the card lets you type into the dimension boxes beside the labelled diagram. Generic equatorial is a plausible mid-size mount for getting started; picking any library mount fills the same boxes, read-only. Tick Use my own values to unlock them and adjust from there; untick to put the published figures back. Measure A vertically from the pier flange to the RA pivot, B from that pivot to the declination axis along the polar axis, and C from the declination axis across to the optical axis. I, the counterweight shaft, is optional. For an alt/az mount there is a single measurement, H, from the pier flange to the altitude axis.
Because B runs along the polar axis, the declination axis sits at A + B × sin(latitude) above the flange, so the figure follows your site. Any box left at 0 leaves the corresponding value alone.
Selecting Alt/Az sets the pier height to 6″. The L-500 carries its altitude axis 32.3″ above the pier flange, so a 6″ pier puts that axis level with the 38″ dome springline — the swing sphere then sits concentric with the hemisphere, which needs the smallest dome. Your equatorial pier height is restored if you switch back.
Equatorial (GEM) draws a German equatorial with a latitude-tilted RA axis and counterweight shaft. Alt/Az or Fork draws a PlaneWave L-500 direct drive instead — wide base drum, single offset arm and altitude drive drum. Both are driven from the same calculated sky position, so the picture always agrees with the numbers.
The pier and telescope are drawn as a real German equatorial mount: the head tilts to the site latitude so the RA axis points at the celestial pole, the RA rotor turns with Right Ascension, and the Dec rotor swings the tube about the declination axis. At RA 0h / Dec 90° the mount sits in the park position — counterweight hanging down, tube along the polar axis.
With dual saddle enabled, both tubes are drawn side by side, separated by the lateral axis length you enter. The ghost aperture circles projected on the dome surface, the shutter clearance checks and the hit markers all continue to work for each tube independently.
The pier base always rests on the floor; changing the pier height, diameter or mount-head height rebuilds the model to match.
Drag to orbit, scroll to zoom. The shutter turns red whenever it doesn't clear. Toggle the local horizon and celestial equator from the preview header.
The final answer — Copy NINA Settings copies all eight values to your clipboard as clean, pasteable text.