SCTune is a collimation-assistance app for SCT imaging workflows. It helps you evaluate and visually align a star pattern using either:
Tri-Bahtinov mode
For spike-based analysis and overlay guidance
Normal Star mode
For manual concentric-circle alignment on a defocused star
This guide is written for the current simplified SCTune interface, where the main controls are focused on:
starting and stopping the preview
loading a test image
using a synthetic source
capturing an external app window such as ASIAIR
adjusting the overlay
calculating and reviewing collimation results
Open the ASIAIR app on your Mac and make sure its preview window is visible.
In SCTune, go to the Camera section on the right.
Under Window Capture, make sure the text box contains:
ASIAIR
Click Use external window.
If needed, adjust Crop X, Crop Y, Crop Width, and Crop Height until the preview shows the correct area.
Use Refresh Detection to update the analysis. It may take a few seconds until the detection finds the centre and diffraction spikes.
If the center looks wrong, click Auto Find Centre.
Fine-tune the overlay manually if needed.
Open the target app on your Mac.
Make sure the correct preview window is visible on screen.
In SCTune, go to Window Capture.
In the text box, type the exact app name or a distinctive part of that window’s title.
Click Use external window.
Adjust crop if needed.
Use Refresh Detection.
Click Load Test Image or drag an image directly onto the preview.
Choose the correct mode:
Tri-Bahtinov for spike-based patterns
Normal Star for concentric diffraction rings
Adjust the overlay if needed.
Use Calculate Collimation Error to review the current result.
The app window is divided into three main areas.
This is the large preview area on the left. It shows:
the current image source
the collimation overlay
guidance text
the star pattern you are analyzing
This is also the area where you manually adjust the overlay.
This panel appears below the preview and contains:
Preview Zoom
Reset View
This section controls how the preview is displayed on screen. It does not change the underlying image itself.
This contains the main control panels, including:
Camera
Tri-Bahtinov Status or Normal Star Status
The status panel changes depending on the selected focus mode.
Below the preview, SCTune shows a summary panel with:
guidance
error values
estimated magnitude
most offset sector or circle
a Calculate Collimation Error button
This panel helps you interpret the current result.
For best results:
use a reasonably bright star
make sure the star is clearly visible
keep the star fairly close to the center of the frame
avoid heavy shaking or large focus changes while adjusting the overlay
use enough defocus for the pattern you want to analyze to be visible
If you are using external window capture:
the target app must already be open
the target window must be visible on screen
SCTune needs macOS Screen Recording permission
you may need to adjust the crop after capture starts
The Camera section is where you choose and control the image source.
Starts or stops the live preview stream.
Click Start Preview to begin previewing the current source.
Once preview is running, the button changes to Stop Preview.
Click Stop Preview to stop the preview.
In this simplified build, the older camera device dropdown and manual discover/connect buttons are no longer shown.
Loads a still image file from disk and uses it as the preview source.
Click Load Test Image
Choose an image file
SCTune loads the image into the preview
You can drag an image file directly onto the preview area.
Use this when:
testing the overlay
reviewing a screenshot
comparing saved frames
Switches the preview to SCTune’s internal synthetic test source.
Click Use Synthetic.
Useful for:
testing the interface
testing overlay behavior
learning the app without a real image source
The Window Capture section is used to capture a live view from another app window on your Mac.
This is the feature you use for:
ASIAIR
other astronomy apps
any other app whose visible window contains the star image you want SCTune to analyze
The button is called Use external window because the feature is generic, but it works for ASIAIR as well.
This text box is very important.
It tells SCTune what window to look for when you click Use external window.
SCTune tries to find an open window whose:
application name matches what you typed, or
window title matches what you typed
Use the exact app name whenever possible.
Examples:
ASIAIR
Safari
Preview
Photos
If the exact app name does not work, try a distinctive part of the window title.
Type:
ASIAIR
Type the exact name of the app or a distinctive window title.
Examples:
Safari
Preview
Photos
If the box is left blank, SCTune falls back to:
ASIAIR
So for ASIAIR, leaving it blank may still work, but it is better to type ASIAIR explicitly.
Starts using the window named in the text box as the preview source.
Open the ASIAIR app on your Mac
Make sure the ASIAIR preview window is visible
In the text box, type:
ASIAIR
Click Use external window
Wait for the preview to switch
Adjust crop if needed
Open the target app
Make sure the desired window is visible
Type the exact app name or a distinctive window title into the text box
Click Use external window
Adjust crop if needed
Check:
the app is open
the window is visible
Screen Recording permission is enabled for SCTune in macOS
the name in the text box is correct
These sliders control what portion of the external window SCTune captures.
Moves the capture area left or right.
Moves the capture area up or down.
Changes how wide the captured region is.
Changes how tall the captured region is.
Start external window capture
Look at the preview
If too much of the app UI is visible, reduce Crop Width and/or Crop Height
If the star area is off-center, adjust Crop X and Crop Y
Continue until the preview mainly shows the image area you want SCTune to analyze
These controls only change what part of the external app window SCTune reads. They do not change anything in the external app itself.
Resets the crop sliders back to SCTune’s default window-capture crop values.
Use this when:
the crop has become messy
you want to return to the default capture area
you want to start the crop adjustment over
Below the Window Capture section you will see status lines such as:
State
Source
Shows the current preview or connection state.
Shows the current image source, such as:
synthetic
test image
window capture
The large preview area is where you view and adjust the overlay.
the current image source
the collimation overlay
guidance text
detected center or crosshair
spikes or circles depending on the selected mode
You may see messages such as:
No preview running
Waiting for first frame
If so:
start the preview
load a test image
use the synthetic source
or capture an external window
This section appears below the preview.
Zooms the preview in or out.
move the slider to zoom in for fine adjustments
move it back toward 1.00x to zoom out
Resets:
preview zoom
preview pan position
Use this if:
you have zoomed in and panned around
the image is off-center
you want to return to the default view
When the preview is zoomed in above 1.00x, you can drag the image to pan it, as long as you are not currently dragging an overlay control.
SCTune has two main working modes.
Use this for spike-based analysis and overlay alignment.
Use this for manual concentric-circle alignment on a defocused star.
You choose the mode using the Focus Mode picker in the right-side status panel.
This mode is used when you are working with a Tri-Bahtinov pattern and want to analyze or manually adjust the spike overlay.
In this mode, SCTune can show:
the detected automatic spike overlay
the detected center crosshair
overlay labels
the symmetric manual guide
guidance text and summary data
Runs detection again using the current frame and current settings.
Use it when:
the image source changed
the crop changed
the overlay is stale
the star moved
you want a fresh result
Requests a fresh automatic center find and refreshes detection.
Use it when:
the center looks wrong
the overlay is anchored incorrectly
the star has shifted
you want SCTune to try finding the center again automatically
This button appears when SCTune has a processed frame.
Moves the manual guide center to the currently detected star position.
It does not:
move the telescope
move the focuser
change the camera
re-run detection by itself
It only repositions the manual guide overlay inside SCTune.
Use it when:
you are showing the manual guide
you want the guide centered on the detected star quickly
Shows or hides sector labels on the overlay.
Turn this on if you want to see sector labels clearly.
Turn it off if you want a cleaner view.
Shows or hides the automatic detected overlay.
When enabled, SCTune draws the detected center and spike overlay.
When disabled, the automatic overlay is hidden.
If you want to manually drag the detected center or a detected spike ray, Show Auto Overlay must be enabled.
Changes the visible size of the crosshair.
Use it when:
the center marker is too small to see clearly
you want a larger or smaller visual target
This changes the display size only.
Controls how transparent or solid the automatic overlay appears.
lower values make the automatic overlay fainter
higher values make it more visible
Use this when the overlay is:
too bright and hides the image
too faint to see well
Changes the thickness of the automatic overlay lines.
Use this when:
the detected spike lines are too thin
you want a bolder or finer overlay
This is one of the main controls for automatic overlay line width.
Shows a manually controlled, idealized reference guide that you can position and rotate yourself.
This guide is separate from the automatic overlay.
Use it when:
you want a clean visual reference
you want to compare the real spikes against an idealized symmetric guide
you want more manual control over the overlay
These controls appear when Show Symmetric Manual Guide is enabled.
Move the center of the manual guide.
You can also move the manual guide by dragging in the preview when the manual guide is shown. If you click directly on the detected center or an auto-detected spike ray, those auto-overlay controls take priority instead.
Rotates the manual guide.
Use this to align the guide with the visible spike orientation.
Changes the overall size of the manual guide.
Changes the separation of the triplet lines in the guide.
Changes the color of the manual guide.
Changes how transparent or solid the manual guide appears.
Changes the thickness of the manual guide lines.
These are the main controls for manual guide appearance.
There are two main manual adjustments you can make to the auto overlay.
Use this if the center crosshair is not exactly on the star center.
Make sure Show Auto Overlay is enabled
Move your mouse over the detected center crosshair
Click and drag the crosshair to the correct center
Release the mouse
When you release, SCTune recalculates using the adjusted center position.
Use this if one of the detected spike rays does not line up with the visible diffraction spike.
Make sure Show Auto Overlay is enabled
Move your mouse over the spike ray you want to correct
Click and drag that ray so it lines up better with the actual spike
Release the mouse
When you release, SCTune recalculates using the adjusted ray position.
zoom in first for finer control
make small adjustments
correct the most obviously wrong ray first
if the overlay becomes messy, use Refresh Detection or Auto Find Centre to get a fresh starting point
You are not changing the underlying image. You are changing SCTune’s overlay interpretation.
If the overlay is hard to compare against the star pattern, adjust these controls:
Auto Overlay Opacity = transparency of the detected overlay
Auto Line Thickness = line width of the detected overlay
Guide Opacity = transparency of the manual guide
Guide Thickness = line width of the manual guide
Crosshair Size = visible size of the crosshair
A good workflow is to slightly reduce opacity and increase thickness until the overlay is visible without hiding the star pattern.
Normal Star mode is used for manual concentric-circle alignment on a defocused star.
In this mode, automatic detection is paused and you manually position a crosshair and circles over the star pattern.
The goal is to make the circles line up with the diffraction rings as evenly and concentrically as possible.
In Normal Star mode, the right panel includes:
Crosshair Size
Circle Count
Selected Circle
Radius
Reset Circles
Calculate Collimation Error
Changes the visible size of the crosshair so it is easier to place on the star center.
Sets how many circles are available.
1 to 8 circles
Use fewer circles if only a few rings are clearly visible.
Use more circles only if you can place them confidently.
When a circle is selected, SCTune shows:
which circle is selected
a Radius slider for that circle
In the current build, a circle is resized using the Radius slider.
Do not expect a resize handle in the preview.
This is one of the most important parts of the app.
Move the mouse over the crosshair
Click and drag it to the center of the star
Release
Move the mouse over the ring itself
Click near the ring line
Drag to reposition that circle
Release
When you click a circle, SCTune selects it so that its radius can be adjusted with the slider.
Click the circle you want to edit
In the right panel, find Selected Circle
Use the Radius slider to change that circle’s size
In the current build, resizing is done with the Radius slider, not by dragging a resize handle in the preview.
Center the crosshair first
Start with the most obvious diffraction ring
Move the ring into place
Resize it with the Radius slider
Continue with the next ring
Use only as many circles as you can place confidently
It is better to fit fewer circles accurately than many circles poorly.
Restores the circles to their default arrangement.
Use it when:
the circles have become messy
you want to start over cleanly
you are not happy with the current layout
You may see this button in two places depending on what is currently shown:
in the right-side panel in Normal Star mode
in the Collimation Data panel below the preview
Calculates the current collimation result using the overlay as it is currently positioned.
Use it after:
positioning the circles in Normal Star mode
adjusting the detected center or spike rays
making manual overlay changes and wanting updated results
The Collimation Data panel below the preview summarizes the current result.
Depending on the mode, it may show:
confidence
estimated collimation magnitude
max delta
average error
asymmetry
most offset sector or circle
guidance text
Use this panel to judge whether your changes are improving the pattern.
Typical questions it helps answer:
is collimation improving?
which sector or circle appears most off?
is the pattern becoming more symmetric?
Open ASIAIR on your Mac
Make sure the ASIAIR preview window is visible
In the text box, enter:
ASIAIR
Click Use external window
Adjust crop until the correct image area is captured
Use Tri-Bahtinov mode
Click Refresh Detection
If needed, click Auto Find Centre
Manually drag the center or a spike ray if necessary
Adjust opacity and thickness so the overlay is easy to compare with the image
Save a frame from ASIAIR or another app
Click Load Test Image or drag the image onto the preview
Choose the correct focus mode
Adjust the overlay
Review the guidance and summary data
Switch Focus Mode to Normal Star
Move the crosshair to the star center
Select and move circles one at a time
Resize the selected circle with the Radius slider
Click Calculate Collimation Error
Review which circle is most offset
Check:
the target app is open
the target window is visible
Screen Recording permission is enabled for SCTune
the correct app name is in the text box
Adjust:
Crop X
Crop Y
Crop Width
Crop Height
Try this order:
Refresh Detection
Auto Find Centre
zoom in
drag the center crosshair if needed
drag a spike ray if needed
Adjust:
Auto Overlay Opacity
Auto Line Thickness
Guide Opacity
Guide Thickness
Crosshair Size
Remember:
move the crosshair by dragging the crosshair
move a circle by clicking near the ring and dragging it
resize the selected circle with the Radius slider
Use Reset View.
Start Preview / Stop Preview: starts or stops the preview
Load Test Image: loads a still image from disk
Use Synthetic: switches to the synthetic test source
Use external window: captures a live app window such as ASIAIR
Reset Crop: resets external window crop to default values
Refresh Detection: reruns detection
Auto Find Centre: asks SCTune to automatically find the center again
Center Guide on Detected Star: moves the manual guide center to the detected star
Reset Circles: restores circles to default positions
Calculate Collimation Error: calculates the current result from your current circle placement
Reset View: resets preview zoom and pan
Calculate Collimation Error: recalculates the current error and summary using the currently displayed overlay
For the smoothest learning curve:
Start with ASIAIR or a saved test image
Learn Tri-Bahtinov mode first
Practice:
refreshing detection
auto-finding center
dragging the center crosshair
dragging a spike ray
adjusting opacity and thickness
Then move to Normal Star mode and practice:
centering the crosshair
moving circles
resizing the selected circle with the Radius slider
Once those two workflows feel natural, SCTune becomes much faster and easier to use in real collimation sessions.
For support, feature requests, or bug reports, contact:
Email: LedgerSlip@gmail.com