PiFinder™ User Manual
Note
This documentation covers rev4, v3 and v2.5 PiFinders running software 2.2.0 or above. You can see which version you’re running in the upper right of the welcome screen.
Not sure which you have? See Which PiFinder do I have? in the Quick Start.
For docs covering a previous version, see 1.x.x, 2.0.x or 2.1.x.
Thanks for your interest in the PiFinder! This guide describes how to use one. To build one, see the Build Guide and the Bill of Materials.
The manual has sections you can reach from the links to the left. Let’s dig into what the PiFinder can do.
How It Works
The PiFinder is a self-contained telescope positioning device. It tells you where your telescope is pointed, lets you select an object such as a galaxy or another deep-sky object, and directs you on how to move the telescope to find it. It has other useful features alongside these core functions, but its main purpose is to get interesting objects into your eyepiece for a look.
To direct you, the PiFinder needs to know where your telescope is pointed. It works this out directly. It photographs the night sky and examines the star patterns to determine which section of sky it sees. It does this quickly, up to 20 times per second, and very accurately. This only works while the telescope is still, so the PiFinder pairs the camera with an accelerometer that estimates how far the telescope has moved since the last solve. The Status screen and the Settings menu call this sensor the IMU. The estimate carries some error, but the moment you stop, a fresh photo corrects it. The PiFinder works out its own orientation as it solves, so you can mount it at any angle. It does not need to sit upright, as long as the camera points the same way as your telescope.
The PiFinder knows where your telescope points and where thousands of interesting objects sit, so it can show you how to move the telescope to bring any of those objects into your eyepiece. Because it measures where the telescope actually points, you can trust its guidance.
Note
For a general overview of using the PiFinder, read the Quick Start. This manual goes deeper but doesn’t cover the first-time set-up steps in the Quick Start.
The Menu System
You reach all of the PiFinder’s functions through its menu system:
Each menu is a list of items. A menu item leads to a submenu, a screen, or a set of options. Scroll through a menu and select items with these keys:
The UP and DOWN arrows scroll the current menu
The RIGHT arrow selects the current menu item, which either sets an option or opens another menu
The LEFT arrow takes you back to the previous menu or screen
Press and hold LEFT for more than a second to jump back to the TOP of the menus
The arrows are the four directions of the joystick. Pressing the joystick straight in does the same as the SQUARE key.
Note
On v3 and v2.5 PiFinders the arrows are four separate buttons in a row along the bottom of the keypad rather than a joystick. The key names are the same on both. The v3 manual covers that hardware throughout.
The status bar at the top of the screen shows the name of the menu you’re viewing.
For a bird’s-eye view of every menu and what each menu item does, see the PiFinder™ Menu Map.
Screens
Some menu items, like Camera, lead to a specific screen: a camera preview, a star chart, or details about a catalog object. The sections below cover each screen in more detail.
Options
Some menus present a list of options where you select one or more items to control how the PiFinder operates. For instance, the Set Filters menu item takes you to a sub-menu of ways to filter your object lists:
Select Type to see the deep-sky object types you can use to control which objects appear in your object lists.
Lists that offer selections show a check-mark next to each selected option. Press RIGHT with an option highlighted to select or de-select it.
In menus that allow only a single selection, such as Altitude, selecting one option de-selects any others. Multi-Select menus offer options to select or de-select all items at once.
When you’re done, press LEFT to go back to your last menu or screen.
With this simple set of scroll-and-select tools you can reach all of the PiFinder’s features.
Quick Menu
You can reach everything through the menu system. A secondary quick-menu brings some functions into easier reach.
Press and hold SQUARE to open the Quick Menu.
This menu presents up to four options, one per arrow button. Press an arrow to select its item. The menu changes with the screen you’re on, but it often has HELP at the UP option.
Some Quick Menus have a second layer. The Object List’s Quick Menu, for example, offers Sort and Filter. Press LEFT for Sort to open a ring of sort orders, with subtle shading marking the current one.
Select a sort order to apply it. To exit the Quick Menu at any time, press SQUARE again.
Help System
Many screens offer help with their button functions, and with other details about how things work or what a screen is for.
When available, HELP is the UP option in the Quick Menu
Press UP to select help. Help opens one or more pages. A prompt at the top or bottom of the screen shows when more pages are available. Press UP or DOWN to scroll through them.
Observing with PiFinder
Out under the stars, you do four basic things in various combinations:
Curating a list of objects you’re interested in
Viewing details about those objects
Pushing the telescope to bring them into your eyepiece
Logging your observations
Everyone observes their own way, so use the features you want and skip the rest.
Object List
The Object List is one of the PiFinder’s main features. It presents a collection of objects you’ve selected using catalogs, filters, observing lists, and text search.
To start a list, select Objects from the main PiFinder menu, then select one of five menu items:
All Filtered: All objects across all catalogs that meet your filter criteria. This could be thousands of objects, and it is most useful with strict filters, such as globulars above 30 degrees altitude and brighter than magnitude 10.
By Catalog: All objects from a specific catalog that meet your filter criteria. Great for observing projects and finding the nearest objects in a particular catalog.
Recent: Starts empty and builds a history of the objects you’ve looked at during the current session.
Custom: Enter a right ascension and declination by hand to make a one-off Custom Target. See Custom Targets.
Name Search: Search for objects by name with the number keypad. The Snowball planetary? Cat’s Eye? This is the way to find them.
However you build the list, it always displays the same information and offers the same sorting and selection.
A symbol along the left shows each object’s type. Next to it is the designation, usually the catalog abbreviation and index number, then the distance from your current telescope position. Each entry’s brightness hints at its magnitude.
Press SQUARE to cycle through additional information for the objects on the list.
You can see a scrolling list of common names for each object.
The next press shows the magnitude and size of each object, with a check mark to indicate whether you’ve observed and logged it before.
Press and hold SQUARE to open the Quick Menu, where you can sort and filter this list.
Press LEFT to select SORT
By default, lists use STANDARD order. That is usually the order the objects appear in the catalogs. Press the indicated arrow to select another order such as NEAREST, which puts the object closest to your current telescope position at the top.
If you start typing a number, the Object List jumps to the next object with that index number. Press the UP/DOWN arrows to step to the next or previous match. Press SQUARE to exit jump mode and select an object.
Press RIGHT to open the details for the selected object.
Object Details
Press RIGHT from the Object List to open the Object Details screen for the highlighted object. This screen shows large Push-To instructions, object images, and catalog details.
Press SQUARE to cycle through the object’s information. Press UP/DOWN to move to the next or previous object in the list. LEFT goes back to the full list, and RIGHT opens the Logging interface for the current object.
The Push-To information shows which way, and how far, to move your telescope to put the object in your eyepiece. As you move the telescope the numbers dim, which means the PiFinder is using the accelerometer to estimate where the telescope points. When you stop, or move slowly enough, the camera plate solves to give an absolute position and the numbers brighten again.
When the numbers are near 0.00 the object should be in your eyepiece. The numbers are the distance to the object in degrees, so with an eyepiece offering a 0.5 degree true field of view, getting them below 0.25 (half the true field) should put the object in view.
Closer to zero means more centered. For a very dim object, knowing it’s dead center and consulting the object image can make all the difference.
Note
By default the Push-To arrows guide you in altitude and azimuth, the way an Alt/Az or Dobsonian mount moves. On an equatorial mount, set Mount Type to Equatorial in the Settings Menu. The guidance then switches to right ascension and declination to match your mount’s axes.
Leave Mount Type on Alt/Az if you use an alt-az telescope on an equatorial tracking platform. You still move the telescope in altitude and azimuth, and the PiFinder corrects for the platform’s rotation on its own.
The number in the upper right is the object’s contrast reserve. It estimates how easily the object should show in your eyepiece tonight.
The PiFinder can show images of all the extended objects in its catalogs. See the section on object images below for more.
Depending on the catalog, the PiFinder may have detailed notes alongside the object’s type, constellation, magnitude, and size. It gives the size in degrees, arcminutes, or arcseconds, whichever best suits the object. Use the +/- keys to scroll the notes.
Many objects carry more than one catalog designation, and the notes can gather a description from each. A bright horizontal rule labelled with the catalog and number, for example NGC 6543, separates one catalog’s notes from the next, so you can see at a glance where each note comes from. The notes finish with a count of how many times you’ve logged the object, marked by its own rule (it reads Not Logged until your first sighting).
What each part of the screen shows
The Object Details screen packs a lot in. These two views label every part. The first is the Push-To screen. The second is the catalog details you reach by pressing SQUARE.
Contrast Reserve
The number in the upper right of the Object Details screen is the contrast reserve. It estimates how easily an object should stand out in your eyepiece. It weighs the object’s brightness and size against your sky brightness, your telescope’s aperture, and the magnification of your active eyepiece, then compares the result to what the eye can detect. A higher number means the object should be easier to see.
Keep pressing SQUARE to reach the Contrast Reserve page, which shows the value on its own with a plain-language reading of what to expect:
Contrast reserve |
What to expect |
|---|---|
Below −0.2 |
Object is not visible |
−0.2 to 0.1 |
Questionable detection |
0.1 to 0.35 |
Difficult to see |
0.35 to 0.5 |
Quite difficult to see |
0.5 to 1.0 |
Easy to see |
1.0 and above |
Very easy to see |
The contrast reserve appears only when the PiFinder has everything it needs to work it out: an active telescope and eyepiece, a sky-brightness reading, and an object with a known magnitude and size. If any of these is missing, the PiFinder leaves the number off. A double star has no single magnitude, for example, and the sky brightness is unknown until the camera has estimated it.
Note
The sky-brightness figure comes from the PiFinder’s Sky Quality Meter (SQM), its camera-based estimate of how dark your sky is. The contrast reserve therefore tracks your real conditions: the same object reads higher under a dark sky than from town. Treat it as a guide rather than a guarantee. Averted vision, transparency, and how dark-adapted you are all play their part at the eyepiece.
Sky Quality Meter
The PiFinder measures how dark your sky is from its own camera. It reports the result in magnitudes per square arcsecond, where higher numbers mean darker skies. To see the reading, select SQM from the main menu.
The screen shows the current figure in large digits, along with the Bortle class that describes the same sky in words. Press SQUARE for a plain-language description of what you can expect to see under a sky of that class.
There is nothing to set up. The PiFinder recognises its own camera and starts measuring when you turn it on. The reading needs no plate solve, so it keeps updating through thin cloud and through frames with too few stars to solve.
The Sky Quality Meter page covers the screen in full, explains what the number means, and describes the optional calibration wizard: when you need it, how to run it, and what it changes.
Star Chart
The Star Chart, reached from the main PiFinder menu, draws a live map of the sky around where your telescope points, with constellation lines and markers for nearby objects. It redraws as you move the telescope, so it is a quick way to see what is around you and confirm your aim. Zoom in and out with the +/- keys.
Deep-sky objects show as small symbols, one shape per object type. Near where you point, the chart marks the objects your filters allow. It reveals fainter ones as you zoom in and keeps only the brightest as you zoom out, so the field never crowds. The chart also marks objects on a loaded observing list. To dim these markers, or switch them off, use the DSO Display setting under Chart… in the Settings Menu.
A brighter cross marks the object you last opened in Object Details, wherever you steer. It is a quick way to see where that object sits relative to your aim. On the chart the cross carries the object’s designation, “M 57” for example. Once the object drifts off the edge, an arrow at the rim points the way instead. The cross stays bright even with DSO Display turned off.
You decide how the chart is turned. Select Coordinate Sys. under Chart… in the Settings Menu:
Horizontal (the default) keeps the horizon level and the zenith up, matching what you see with the naked eye.
EQ (Auto) lines the chart up with the celestial pole: north-up in the northern hemisphere, south-up in the southern.
EQ (North-up) and EQ (South-up) force north-up or south-up wherever you are.
The chart labels what is currently at the top, so you always know how it is oriented. The labels are “Zenith up”, “NCP up” (north celestial pole), and “SCP up” (south celestial pole). The same orientation applies to the Align screen.
Note
The chart works before the PiFinder has a GPS fix. The Horizontal and EQ (Auto) modes need to know where you are to orient themselves. Until GPS locks, or you enter your location by hand, the chart falls back to north-celestial-pole-up. It marks the label with a leading “!”, for example “!NCP up”, to show that the orientation is temporary and settles once your location is known.
Filters
Every object list aside from Name Search and Recent shows only objects that meet the filter criteria you’ve set. View and adjust your filters from the Set Filters menu, the last item in the Objects menu.
You can also reach the filter options from the Quick Menu on the Object List screen.
The Set Filters menu offers several ways to limit which objects appear, plus a Reset All option to clear every filter.
With no filters set, every available object appears. The All Filtered list then shows over 18,000 objects.
Some filter types take a single value, like Altitude, and some allow multiple selections, like Object type. Here’s a brief explanation of each:
Catalogs: Limit which catalogs the All Filtered list includes. This is distinct from the catalog-specific object lists, which are a shortcut to one catalog. Using the Catalogs filter, the All Filtered list can show globular clusters across multiple catalogs at once.
Type: Limit by object type. You can select multiple types to include.
Altitude: The current apparent altitude of an object from your observing location.
Magnitude: Limit to objects at least as bright as the selected magnitude.
Observed: Include only objects you’ve logged, never logged, or any logged state.
Catalogs Filter
The PiFinder has many catalogs, so this menu groups them by category.
Common catalogs appear at the top level for quick reference. Less common ones sit in sub-categories marked with an ellipsis (…).
Here’s the DSO… category as an example:
Selected catalogs show a check box, and you may see the same catalog, like Messier, in multiple spots. Selecting or de-selecting anywhere changes its state everywhere.
Name Search
Name Search is a powerful way to search the PiFinder’s large object database. It finds objects by their common name, like the Cat’s Eye nebula. To reach the Name Search screen, select it from the Objects menu:
It uses multi-tap text input, like the cellphones from the dawn of text messaging. The on-screen keypad shows the letters you get by pressing each number key several times in a row.
Each number key generates its number, then the three or four letters shown, in turn. Pause long enough between presses, or press a different key, and the cursor moves to the next position.
To press each key just once, switch the search input to T9. Every press enters its digit,
and the PiFinder matches the digit sequence against the letters of each object name, so
1897 finds Vega. Select Multi-Tap or T9 under Search Input in the
Settings Menu. You can also press and hold SQUARE here and select
Input from the Quick Menu to reach the setting directly.
As you type, the PiFinder shows how many objects match your search term, to the far right of your text.
The count drops as you add more text.
Once you’ve narrowed the list enough, press RIGHT to see the full list of matches.
Custom Targets
Sometimes the object you’re after isn’t in any catalog: a newly discovered comet, or a position from a chart or article. Select Custom from the Objects menu to enter a right ascension and declination by hand, then push to it like any other object.
Type the coordinates with the number keys. The UP/DOWN arrows move between fields, and - deletes the last digit. Press SQUARE to cycle the entry format: full hours/minutes/seconds (shown above), decimal hours and degrees, or decimal degrees for both. The title bar names the active format. With the declination degrees selected, + flips its sign. On the EPOCH field, + cycles between J2000, JNOW, and B1950.
When the numbers look right, press RIGHT to create the target. The PiFinder makes a one-off object, opens its Object Details screen with Push-To guidance, and adds it to the Recent list so you can return to it during the session. Press LEFT to go back without creating anything.
Observing Lists
You can bring a session you planned ahead of time to the eyepiece, whether you built it in
SkySafari or a spreadsheet, or a fellow observer shared it with you. Copy the list file
into the obslists/ folder of the PiFinder’s shared data
folder, then load it from Obs Lists in the Objects
menu.
The PiFinder reads observing lists in all of these formats. It recognizes each by its file
extension and, for .txt files, by the content itself:
Format |
Extension |
|---|---|
|
|
PiFinder native |
|
CSV |
|
|
|
|
|
|
|
|
|
|
|
Plain text, one object name per line |
|
The Obs Lists screen shows every list it finds, along with any folders. Folder names appear
in [brackets], so you can organize lists into subfolders by trip, season, or source.
Scroll with the UP/DOWN arrows and press RIGHT to open a folder or load a list.
When two lists share a name, such as Messier Marathon.skylist and
Messier Marathon.csv, the PiFinder appends the format to tell them apart, as in the
image above.
Loading a list matches each entry against the PiFinder’s catalogs, briefly reports how many objects matched, and opens the result as a regular Object List you can sort, browse, and push to.
Entries that match a catalog behave exactly like objects you find by browsing. Images, descriptions, and your observation logs all come along. An entry the PiFinder cannot match, but that includes coordinates, becomes a one-off object under the code OBS, so nothing on your list is left behind.
Note
The .pifinder format is the PiFinder’s own JSON list format. Use it when a planning
tool offers it, because it carries catalog references, magnitudes, object sizes, and
coordinate epochs that the other formats drop. The observing-list formats reference
documents its fields, JSON schema, and a worked example.
Importing a CSV list
CSV is the format to reach for when another tool gives you a list as plain columns: a
spreadsheet, an observing planner, or a sky atlas. The first line is a header naming the
columns. The PiFinder reads them by name, so their order does not matter and the case is
ignored. Only Name is required, plus coordinates so the PiFinder knows where to point:
Column |
Holds |
|---|---|
|
A label for the row, e.g. |
|
Right ascension and declination (see the coordinate forms below). |
|
Brightness, optional. |
|
Object type such as |
The PiFinder accepts common spellings of those headers too. ra, dec, mag,
RA_deg and Dec_deg all work. The RA header can also carry the unit: the PiFinder
reads a decimal under RA_h or RA_hours as hours, and one under RA or RA_deg
as degrees. Write coordinates in any of three forms:
Form |
RA example |
Dec example |
|---|---|---|
Decimal degrees |
|
|
Colon-separated |
|
|
Sexagesimal |
|
|
The PiFinder reads a decimal right ascension as degrees (0–360) unless its header names hours. A small list looks like this:
Name,RA,Dec,Magnitude
My target,205.8583,28.2442,6.3
Comet 2024X,250.667,36.411,11.0
Each row resolves the same way as any other observing list. If its name matches a catalog
object, you get that object with its images, descriptions, and your logs. Matching ignores
spacing and capitalisation, so M 13, M13 and NGC 224 all work. If the name
matches nothing, the PiFinder uses the row’s own coordinates as an OBS target. To keep your
exact coordinates for an object the catalog would otherwise recognize, give the row a name
the catalog does not match. A prefix, as in _M 3, is enough.
For the complete column reference, see the observing-list formats reference. It covers every accepted header spelling, the coordinate forms, and the import notes.
Object Images
If you used the prebuilt PiFinder image, or have downloaded the set of catalog images, you can see what the selected object looks like in sky-survey images. These appear in the background of the Object Details screen. Press the SQUARE key to cycle through the pages of information about each object and view the images in full detail.
The PiFinder rotates each image to match the view through your eyepiece at your position and time, which helps you identify the faintest objects.
Zoom in and out with the +/- keys. The FOV appears at the bottom of the image, so you can match it to your eyepiece.
As an example, here are the images available for M57
These images match the view through your eyepiece for the telescope you’re using, pointing at a specific area of sky from your current location. By default they are oriented for a Newtonian reflector. If you use a refractor, or an SCT with a star diagonal, set the orientation options for your telescope as described in Equipment. Use the + and - keys to switch between the fields of view of the eyepieces you configured in the Web Interface.
Two overlays help you read the image. Letters near the edge of the field mark the cardinal directions, so you can relate the view to a chart. You see two of N, S, E, and W, depending on how the image is rotated. A thin outline traces the object’s cataloged size and orientation. When only the bright core shows in the eyepiece, that outline gives you a feel for the object’s full extent. You can switch both overlays off under Image… in the Settings Menu.
The bottom left of the screen shows the source of the current image, and the left side shows the current FOV information.
Logging Observations
Press the RIGHT arrow while viewing any object’s details to open the logging interface. There you add context about your observation and save it to your log.
Use the UP/DOWN arrows to select one of the four context items to change:
Observability: How easy is it to spot and recognize this object
Appeal: Your overall rating. Would you recommend it to a friend?
Set these first two with a number key from 1 to 5, or press the RIGHT arrow to cycle through the stars.
Conditions…
Transparency: A relative measure of contrast.
Seeing: The stillness of the atmosphere.
Eyepiece: Note which of your eyepieces you’re using.
When you’re done, use the UP/DOWN arrows to select SAVE LOG and record your observation. You can also save straight away, with no context, just to note that you observed an object.
Observing Projects
If you’re like me, you may enjoy observing projects, such as working through all the Messier or Herschel objects. The PiFinder makes these long-term efforts easy. Log each object, and it then shows you only the objects you have left that are visible during a session.
Combine a filter on observation status with an object list sorted by NEAREST to work through a collection easily.
Power & Charging
Every rev4 PiFinder has an internal battery, good for a full night on a single charge. You can also keep one running indefinitely from any USB-C power source. This section covers the power button, how charging behaves, what the battery indicator tells you, how long a charge lasts, and how to look after the cell. For the first time you turn one on, the Powering the PiFinder section of the Quick Start walks through it step by step.
Power button and shutdown
To turn the PiFinder on, press and hold the button marked PWR, on the front below the keypad, for about two seconds. The PWR label lights while the PiFinder starts up, and goes out once the screen and keypad come up.
To shut down, press and hold the button again for about a second. The screen goes straight to the shutdown confirmation. A second press confirms it, a tone plays, and the PiFinder turns itself off once it has closed everything down safely. In normal use you never need to cut the power by hand. If the software ever hangs and will not shut down, press and hold PWR for more than 14 seconds to reset the power system. See The PiFinder won’t turn on.
The menus get you to the same place if your hands are already on the keypad. See Shutdown.
Note
On v3 and v2.5 PiFinders power is a small white slide switch above the screen: facing the screen, slide it right for on and left for off. Shut down from the menus first, then slide the switch off. The v3 manual covers that hardware throughout.
Charging
Two USB-C ports sit on top of the case, each named on the faceplate just below it:
POWER runs the PiFinder and charges the battery. This is the one to plug a charger or a power bank into.
DATA is for connecting accessories, such as the PiFinder remote or other USB devices.
From empty, a full charge takes about six hours with the PiFinder turned off. Charging draws up to 1.5A, so use a supply that can deliver it. A weaker source charges proportionally slower.
You can carry on observing while the battery charges. There is no need to turn the PiFinder off first. Expect the charge to take considerably longer that way, because the PiFinder consumes much of what the charger supplies. A long charge that leaves the battery still low almost always means the PiFinder was running the whole time.
A charge indicator labelled CHG lights while the battery is charging and goes out once it’s full. It is red, but bright enough to be distracting once your eyes are dark adapted, so it’s worth knowing what it is before it appears beside you at the eyepiece.
Note
The last stretch of charging is slow. As the cell approaches full the charging current tapers off, so the CHG light can stay on for a while after the battery is nearly there. That’s normal, not a fault.
Note
v3 PiFinders charge through the optional PiSugar S Plus board rather than an on-board charger. Charge a v3 with the slide switch off, because one left running barely fills at all. Use the port nearest the back of the case. Its indicator glows blue while charging and green when full, and a full charge takes roughly three hours. The port nearest the keypad runs the PiFinder without charging. It is wired ahead of the slide switch, so plugging into it turns a v3 on regardless of the switch position. The v3 manual covers that hardware throughout.
The battery indicator
The title bar carries a battery glyph, just left of the GPS and solver icons.
It estimates how much longer the PiFinder will run, not how much charge is left in the cell. Take it as a guide to the rest of the evening rather than a precise figure, and expect it to err on the cautious side.
The glyph empties in coarse steps rather than counting down smoothly, and shows a hollow outline for the last stretch.
While the battery is charging, a bolt appears in place of the usual glyph.
Note
v3 and v2.5 PiFinders have no battery indicator. The PiSugar board’s charge state isn’t visible to the PiFinder software, so nothing appears in the title bar. The v3 manual covers that hardware throughout.
Low-battery warnings and automatic shutdown
The PiFinder warns you twice as the battery runs down: once when the estimate reaches 10%, and again at 5%. Each is a brief message on screen with a sound to match.
Measured on the bench under a continuously solving load, the 10% warning arrives about an hour and a half before the end, and the 5% warning about half an hour before it. Lighter use stretches both. Each warning appears once per discharge rather than repeating, so it does not nag you for the rest of the night. Plugging in re-arms them for next time.
When the battery is nearly flat, the PiFinder shows a final warning, plays the shutdown tone and shuts itself down cleanly. It stops deliberately rather than letting the power cut out on its own.
Battery life
A full charge of the 8,000mAh cell runs the PiFinder for about ten hours. Treat that as a floor rather than an average. It was measured with the camera solving continuously, the screen at full brightness and the screen sleep turned off, which is harder work than a real night at the eyepiece. Sitting on one object, or stepping away from the telescope, lets the PiFinder drop into power-save mode and stretches the time considerably. Turning the brightness down helps too. Hold SQUARE and press + or - to adjust the screen and keypad at any time.
Note
The PiFinder drops into power-save mode after it has been idle for a while. It dims the screen and slows the camera to save power. Any key press, or movement of the telescope, wakes it. You can change the idle time, or turn it off entirely, in the Settings Menu.
Running on external power
Any USB-C source rated for at least 2A runs the PiFinder: a wall charger, a USB power bank, or a portable power station’s USB output. Plug it into the POWER port. The PiFinder then runs from it and tops the battery up at the same time, and you can add external power mid-session without restarting. As a rough guide, about 1,000mAh of power-bank capacity runs the PiFinder for an hour, so a 10,000mAh bank is good for the better part of a night.
If you hit power dropouts, suspect the cable first. Some USB-C cables are unreliable at the ~2A the PiFinder draws, especially on long runs.
Note
On a v3, the port nearest the keypad runs the PiFinder without charging. That makes a useful trick for stretching a long night. Plug a power bank into that port and turn the battery off. The PiFinder then runs on external power, with the cell held in reserve for after you unplug the bank. The v3 manual covers that hardware throughout.
Warning
Feed the PiFinder 5V USB-C power only. To run it from a telescope’s 12V supply, you must use a 12V-to-5V step-down (DC-DC) converter with a USB-C output. Never connect 12V directly to the PiFinder. That will damage it.
Battery safety & care
The internal battery is a lithium-polymer (LiPo) cell. Treat it sensibly and it lasts for years, but like any lithium battery it deserves a little respect.
Warning
Stop using the battery and disconnect power if it ever becomes swollen, damaged, unusually hot, or develops an odour. A puffed-up or punctured LiPo cell can vent or catch fire. Do not continue to charge or use a cell in this condition. Contact us about a replacement.
Warning
Do not puncture, crush, drop, or open the battery, and don’t open the case to get at it. Keep the PiFinder dry. The battery and electronics are not waterproof.
A few habits keep the cell healthy:
Charge through the POWER port only. The PiFinder’s own charger looks after the cell, so just supply 5V USB-C as described above. There is no need for an external LiPo charger, and you should not connect one.
Charge where you can keep an eye on it, and not on or near anything flammable. Do not charge or leave the PiFinder in extreme heat. A closed car on a sunny day is the classic way to cook a battery.
Mind the temperature. Observers report using the PiFinder from about -15°C (5°F) to 45°C (110°F). That range describes the whole PiFinder in the field, not a separate battery rating. Capacity drops in the cold, though the computer’s own heat keeps the cell warm enough to work in most conditions. Do not charge a battery that is below freezing.
For long-term storage, leave the cell partly charged rather than full or empty and keep it somewhere cool and dry. Top it up every few months so it does not discharge completely.
Dispose of it responsibly. Take a worn-out lithium battery to a battery-recycling drop-off, not the household rubbish.
Note
On a v3, the battery and its charger are the optional PiSugar S Plus 5000mAh board, which is also the only compatible replacement part. Other PiSugar models share the I2C bus with the PiFinder’s motion sensor and cause problems, so make sure you fit the S Plus. Don’t attempt to disassemble the board itself. The v3 manual covers that hardware throughout.
Settings Menu
All user-configurable items live in the Settings Menu, near the bottom of the main PiFinder menu.
The top items collect several options under User Preferences, the Chart Screen, and the object image overlays. An ellipsis (…) indicates more options below.
Below the general UI options are settings for which WiFi mode your PiFinder is in, and for its physical configuration.
The Advanced submenu, near the bottom of the Settings Menu, holds the hardware setup you normally configure once: PiFinder Type, Camera Type, and GPS Settings (type and baud rate). Opening it shows a brief “Options for DIY PiFinders” reminder, because on a fully built PiFinder these already match your hardware.
Sounds
A rev4 PiFinder has a small buzzer. It plays a short tone on each key press, at startup and shutdown, and with every low-battery warning. The Volume menu item, in User Preferences, sets how loud they are. Its options are Off, or 1 through 5. Selecting a level plays a sample tone at that level, so you can set it by ear.
The tones vary in loudness by design: the buzzer is far louder at some pitches than others, so a cue pitched away from its loudest note sounds softer. Set Volume to Off if you’d rather observe in silence.
Note
v3 and v2.5 PiFinders have no buzzer. The Volume setting appears on those PiFinders too, but nothing sounds. The v3 manual covers that hardware throughout.
Connectivity
The PiFinder hosts its own WiFi network, PiFinderAP (no password), so your phone or
tablet can join it anywhere. It can also join your home network instead. Switch between
the two modes from the Settings Menu, and check the current mode and
address on the Status Screen. From a connected device the PiFinder
answers at http://pifinder.local. The Connecting to Your PiFinder page covers the web
interface, SkySafari and other planetarium apps, and the shared data folder.
Tools
Near the bottom of the main PiFinder menu, the Tools menu item leads to a set of screens that aren’t observing-related but provide useful information or let you perform actions: checking the PiFinder’s status, selecting your active telescope and eyepiece, setting your place and time by hand, updating the software, and shutting down or restarting.
For the full tree and a note on what every item does, see the Tools section of the Menu Map. The sections below cover the screens you reach for most often.
Status Screen
The Status Screen is the central place to check the PiFinder’s current state and operation.
Some of the key information shown:
The current solver state, as LAST SLV on the top line. It shows the seconds since the last plate solve, the solve type (i for IMU or C for camera), and, for a camera solve, the number of stars matched.
WiFi information a bit further down, including the current WiFi mode, network name, and IP address.
Place & Time
The PiFinder needs to know where and when it is to turn the sky’s coordinates into the directions it gives you. Its built-in GPS handles this automatically. You do not have to wait for a fix, or have GPS at all, to get going. Open Tools, then Place & Time, to set everything by hand.
Set Location gathers the ways to manage your observing site:
Enter Coords lets you type your latitude, then longitude, then altitude with the number keys. The + key flips the sign for southern latitudes and western longitudes.
Load Location recalls one of your saved sites, and Save Location stores the current one so you can select it again next time.
Set Time/Date sets the clock when there’s no GPS. Enter the time, and the PiFinder moves on to a date-entry screen. The PiFinder protects a time you set by hand, so a later GPS fix does not overwrite it and your manual clock stays put. Reset Location and Reset Time/Date discard what’s set, if you’d rather start fresh or hand control back to GPS.
Note
With your location and time set by hand, the PiFinder is fully usable without a GPS signal. You can focus, align, browse objects, and push to them. The Star Chart and Align screens also work before a GPS lock.
Getting a GPS lock
The PiFinder’s GPS receiver takes a few minutes to work out where it is. This is normal, and it is the part of the first night that surprises people most. Knowing what the receiver is doing saves you from chasing a fault that isn’t there.
Before it can fix a position, the receiver has to download orbit data from the satellites themselves. That download runs at a slow, fixed rate, so it takes several minutes however good your sky is. Expect longer after the PiFinder has been off for a while, or when you have travelled a distance since the last session. Later nights at the same site are quicker, because the PiFinder still holds usable data.
Open the Start menu and select GPS Status to watch progress. That screen turns the camera off, which cuts electrical noise and helps the receiver hear more satellites. It shows Lock boost on while it does this. Leave the PiFinder on that screen and let it work.
Four things are worth knowing while you wait:
“Sats seen/used: 0/0” is not a progress bar. It reads 0/0 for most of the wait and then climbs quickly near the end. A long run of zeros does not mean the receiver has failed or that the sky is blocked.
Leave the PiFinder on. Turning it off and on again restarts the download from the beginning. Rebooting every few minutes to check on it is the one reliable way to never get a lock.
Your phone is not a fair comparison. Phones use assisted GPS. They download the same orbit data over the mobile network in seconds and already know roughly where they are. A phone showing dozens of satellites next to your PiFinder tells you nothing about conditions.
Give the receiver a clear view. It needs open sky. Indoors, under a roof, or hard up against a wall all slow it down or stop it.
Once the fix arrives, the Lock Type on the GPS Status screen tells you how good it is:
Accurate is a 2D fix. It gives latitude and longitude without altitude.
Precise is a 3D fix, which adds altitude.
Both are plenty. The PiFinder only needs a rough position on Earth to point your telescope, so a night that reads Accurate works exactly as well as one that reads Precise. Limited and Basic appear before a full fix, while the receiver is still settling.
Note
You do not have to wait. If the sky is good and you would rather start observing, enter your location and time by hand as described above. Everything works from there.
Update Software
The PiFinder can download and install software updates directly from its screen and keypad. To start, select Software Upd from the Tools menu.
Updates happen on the PiFinder itself, so there is no need to send it anywhere. New PiFinders often ship a version or two behind the latest release, so running an update is a normal part of your first night out.
The PiFinder needs internet access, so put it in Client Mode connected to a WiFi network. See Connecting to a new WiFi network for details.
The PiFinder confirms it can reach the internet, then compares the current release version to the one installed.
Note
If the release version shows as unknown, the PiFinder cannot reach the internet to check. It is either in Access Point mode, or its WiFi is not configured. Put it in Client mode on a network with internet access (see Connecting to a new WiFi network). Re-imaging the SD card is not the fix for this. If WiFi is configured but the check still fails, move closer to the router or re-enter the network details.
If a new version is available, select the option presented to start the update. This may take several minutes, and the PiFinder restarts when it’s done.
You can also download a pre-built image of any software release and write it to the PiFinder’s SD card. See our release page for information about each release and a download link.
Instructions for writing release images to an SD card are on the software setup page.
Polar Alignment
An equatorial platform or equatorial mount tracks the sky by turning your telescope around a single axis that’s meant to point at the celestial pole. That axis is the platform’s pivot, or the mount’s right ascension axis. The closer it is to the true pole, the longer objects stay put in the eyepiece. The Polar Alignment tool measures how far your axis sits from the pole and walks you through correcting it. It works from ordinary plate solves, so you need no polar scope and no sight of Polaris.
It lives near the bottom of the main menu: open Tools, scroll down to Experimental, and select Polar Align.
The tool solves the sky at two or three points while you rotate around that axis between them. You turn the platform, or slew the mount in right ascension only. The PiFinder then works out where the axis points from how the view shifts. The measurement is only as good as the solves behind it, so before you start make sure the PiFinder has a GPS lock, is focused, and is solving reliably. Turn your mount’s or platform’s sidereal tracking off as well, because the measurement assumes the telescope holds still except when you rotate it yourself.
Note
This aligns the rotation axis, not the PiFinder to your eyepiece. The one rule that matters: between captures, move only around that axis. On a platform, keep the telescope clamped to the platform and rotate the platform. On an equatorial mount, lock the declination axis and slew only in right ascension. During adjustment, move the axis itself with your altitude and azimuth adjusters, not by slewing the telescope.
To take a measurement, open Polar Align and press SQUARE to begin, then:
Aim the telescope near the pole and wait for the screen to report a recent solve. Press SQUARE to capture the first point. Getting a good measurement below gives the best aim and sweep for each mount.
Rotate around the axis by at least about 10°, turning the platform or slewing in right ascension only. Wait for a fresh solve, then press SQUARE for the second point.
For a stronger result, rotate farther and capture a third point. Three points let the PiFinder check how well the captures agree. To stop at two points instead, press 0 to solve now.
If the screen says ‘Rotate more’, the captures were too close together to pin down the axis. Rotate farther and capture again.
Once it has enough rotation, the PiFinder switches to a live readout showing how far the axis is from the pole, as push-to offsets in altitude and azimuth. Turn your altitude and azimuth adjusters to follow the arrows until both readings fall to zero. On a platform those are the platform’s adjusters. On a mount they are the polar-alignment bolts. The readout refreshes with each new solve. If it shows ‘No solve’, hold everything still until the PiFinder solves again.
Note
Before touching the adjusters, lock both of the mount’s axes. Right ascension is the one everyone forgets, because you unlocked it to rotate between captures. A clutch that slips while you work the adjusters quietly ruins the correction. On a platform, leave the telescope alone entirely and adjust only the platform.
Note
Turn Sleep Time off before you start. Adjuster knobs move the telescope too slowly for the motion sensor to notice, so the screen dims part way through an adjustment even though you are working. Only key presses hold the PiFinder awake, and the longest sleep delay is 2 minutes, so Off is the setting that suits this job. Sleep Time sits under User Pref in the Settings Menu.
The same applies to a motorized mount at guide speed. A slow slew may not register as motion, so the Push-To numbers appear to freeze and then jump when the PiFinder wakes.
The top line summarises the measurement: the number of points used, the total sweep, and,
for a three-point solve, a fit rating of ok, mid, or bad. A poor fit usually
means something moved between captures that shouldn’t have, so it’s worth redoing.
Press and hold SQUARE to open the Quick Menu, which gathers the advanced actions. STATS opens a read-only detail view. REDO PT drops just the last point so you can recapture it. Roll On/Off switches between a full three-axis fit and an RA/Dec-only fit that ignores camera roll, which is useful after a camera flop. Getting a good measurement covers which fit suits each mount.
The STATS view spells out the correction in both degrees and arcminutes for each axis, the fitted axis position, the fit quality, and how the captures were spaced in time. That detail helps you judge whether a measurement is trustworthy.
To start a fresh measurement at any time, press SQUARE. To exit the tool, press MINUS.
Getting a good measurement
The connection between the PiFinder and the telescope is never perfectly rigid. Small flexures grow with how much the PiFinder’s attitude changes between captures, and they show most strongly in camera roll. Wider sweeps are better in theory, but in practice the sweet spot is a moderate sweep taken close to the pole, which keeps the PiFinder’s attitude nearly constant.
On an equatorial mount:
Point the declination axis so the telescope sits roughly 7–10° off the mount’s polar axis. Measure from wherever that axis points now, not from where the true pole is.
Sweep roughly 30–45° in right ascension: take the middle capture with the PiFinder’s screen roughly vertical, and the first and last captures 15–22° either side of it.
Set Roll Off in the Quick Menu. Flexure shows up most strongly in roll, so the fit is better without it.
On an equatorial platform:
Aim the telescope close to Polaris, ideally within 5°.
Keep Roll On. Aimed this close to the axis, the pointing barely shifts between captures, so the roll change carries most of the rotation information.
Position the PiFinder so its screen is vertical at the middle of the platform’s travel. That also keeps the altitude and azimuth arrows matching the real directions while you adjust.
Expect the result to land within 20–30 arcminutes of the pole. A very rigid connection between the PiFinder and the telescope, plus a wider sweep, can bring that down to around 10. That won’t match a polar scope, or a routine that images through a rigidly mounted telescope with a much smaller field of view. It is still a solid alignment when the pole is hidden from your site or you have no polar scope, and it is close enough to put Polaris into a polar scope’s reticle.
Shutdown
You do not strictly have to shut down before you cut the power, but the PiFinder is a computer and skipping the shutdown risks file corruption. Some MicroSD cards are more sensitive than others.
The quickest route is the power button. Press and hold it for about a second, and the confirmation below appears from wherever you are.
Press the power button again, or the RIGHT arrow, to confirm. Press the LEFT arrow to go back. The screen and keypad turn off within a few seconds, and the PiFinder turns itself off.
The keypad gets you to the same screen. The Tools menu offers a Shutdown menu item under Power, and the Quick Menu is faster:
Press and hold LEFT for more than a second to jump to the main menu
Press and hold SQUARE to open the Quick Menu
Press DOWN to select the SHUTDOWN option
Note
On v3 and v2.5 PiFinders there is no power button, so use the keypad route above. Once the screen and keypad turn off it’s safe to slide the power switch off or unplug the battery. The v3 manual covers that hardware throughout.