Guiding

The Guiding screen controls your autoguider, which monitors a star through a guide camera and sends corrections to the mount to maintain accurate tracking. ARIS integrates with PHD2-compatible guiding backends and provides a full guide interface with star selection, guide graph, star profile, and aggressiveness tuning.

Guide Camera Setup

Star Selection

When you open the Guiding screen, the guide camera view displays the field with detected stars. ARIS auto-selects a suitable guide star near the center of the frame based on brightness and isolation.

To select a different star, tap it directly in the camera view. A good guide star is:

• Bright but not saturated — Check the star profile (see below) to confirm the peak is not clipped.
• Isolated — No nearby stars that could confuse the centroid calculation.
• Away from the edge — Edge stars may move out of frame during dithering.

Exposure and Gain

• Exposure — Set the guide camera exposure using the wheel picker. 1-3 seconds is typical. Shorter exposures give faster correction response but may not have enough signal for faint guide stars. Longer exposures smooth out seeing but slow down the correction loop.
• Gain — Set high enough to clearly see guide stars without saturating them. The guide camera usually runs at higher gain than the imaging camera.

Tip

Aim for a guide star SNR of 10 or higher. The SNR readout appears in the star profile panel. If SNR is low, increase exposure or gain.

Zoom

Tap the zoom button to cycle through 1x, 2x, and 4x magnification on the guide camera view. Higher zoom helps verify star selection and check for elongation or double stars.

Calibration and Guiding

Starting Calibration

Before guiding can begin, the system must calibrate by moving the mount in each axis and measuring the response.

1. Select your guide star.
2. Tap Guide. If the system has not been calibrated (or calibration has been cleared), it runs calibration automatically before starting to guide.
3. During calibration, you will see the mount make small moves in RA and Dec while the system measures the guide star displacement. This takes 30-60 seconds depending on your settings.
4. Once calibration completes, guiding begins immediately.

Note

Calibration is stored per-side for German equatorial mounts. After a meridian flip, ARIS automatically applies the flipped calibration. You do not need to recalibrate unless you change the guide camera orientation or optical path.

Stopping Guiding

Tap the Stop button to halt guiding. The guide camera continues looping frames so you can monitor the field, but no corrections are sent to the mount.

Guide Graph

The guide graph is the primary tool for evaluating tracking performance. It plots correction errors over time for both axes.

• RA (blue line) — Right Ascension tracking error in arcseconds. Periodic error from the mount shows as a repeating sine wave. Wind appears as irregular spikes.
• Dec (red line) — Declination error in arcseconds. Should be relatively flat for a well-aligned mount. Persistent drift indicates polar alignment error.
• RMS values — Displayed above the graph for each axis and combined total. Lower is better. Sub-arcsecond total RMS is good; sub-0.5” is excellent for long focal lengths.
• Scale — The graph auto-scales based on the error range. The dither bounds are shown as dashed horizontal lines.

Toggle the graph visibility from the toolbar. The graph can be dragged to reposition it on screen.

Tip

Watch for patterns in the guide graph. A regular sine wave in RA suggests periodic error that may benefit from PEC training. A steady drift in Dec means your polar alignment needs adjustment. Random scatter in both axes usually points to seeing.

Star Profile

The star profile panel shows a 3D surface plot of the guide star’s intensity distribution. Use it to verify:

• Symmetry — A well-focused, round guide star produces a symmetrical bell curve. Asymmetry may indicate optical issues or a double star.
• Saturation — A flat-topped profile means the star is saturated. Reduce exposure or gain, or pick a dimmer star.
• SNR — The signal-to-noise ratio is displayed in the panel. Higher SNR means more reliable centroid measurements and smoother guiding.

Aggressiveness

Aggressiveness controls how strongly the guider corrects for measured errors. These settings are accessible from the guider settings screen (gear icon).

RA Aggressiveness

Controls the correction strength for Right Ascension errors. Range: 0-100%.

• Higher values — Correct errors more aggressively. Faster response but can cause oscillation if set too high.
• Lower values — Gentler corrections. More stable but allows errors to persist longer.
• Recommended starting point — 70-80% for most mounts. Reduce if you see oscillation in the RA guide graph.

Dec Aggressiveness

Controls correction strength for Declination. Often set lower than RA because Dec errors tend to be slower-moving drift rather than periodic oscillation.

• Recommended starting point — 60-70%. Increase if you see persistent Dec drift that is not being corrected.

Dec Guide Mode

Determines when Dec corrections are applied:

• Auto — Corrects in both directions. Suitable for most situations.
• North only / South only — Only corrects in one direction. Useful when backlash in the Dec axis causes overcorrection. Set this to the direction of your polar alignment drift.
• Off — No Dec guiding. Only use this if Dec is stable and you want to avoid backlash-induced oscillation entirely.

Dithering

Dithering shifts the guide star position slightly between exposures, which helps average out hot pixels, fixed-pattern noise, and walking noise during image stacking. Configure dithering in the guider settings.

• Dither distance — How far to shift in pixels. 3-5 pixels is typical. Larger values give more effective noise reduction but require longer settle times.
• Dither interval — Dither every N frames. Set to 1 to dither between every exposure, or higher to dither less frequently.
• Settle time — How long to wait (in seconds) after a dither move before resuming capture. The guider must return to stable tracking before the next exposure starts. 10-15 seconds is common.
• RA-only dithering — When enabled, dither moves only happen in RA. This avoids Dec backlash issues and is recommended if your Dec axis has noticeable backlash.

Caution

If dither settling takes too long or never completes, reduce the dither distance or increase the settle tolerance. Check the guide graph after each dither to verify the guider returns to stable tracking.

OAG vs Guide Scope

ARIS supports two guide camera configurations, selectable in the guider settings:

Off-Axis Guider (OAG)

An OAG picks off light from the main optical path using a small prism near the sensor. Advantages:

• No differential flexure — the guide camera sees the same optical path as the imaging camera.
• More accurate guiding at long focal lengths.

Trade-offs:

• Smaller field of view makes guide star selection harder.
• Guide stars may be dimmer depending on prism position and vignetting.

Guide Scope

A separate small telescope mounted on top of or alongside the main scope. Advantages:

• Wider field of view with more guide star options.
• Easier to set up and focus independently.

Trade-offs:

• Differential flexure between the guide scope and main scope can introduce errors, especially at long focal lengths.
• The guide image may shift relative to the main camera over the course of a session.

Note

The OAG/Guide Scope setting affects how ARIS handles calibration and guide star brightness expectations. Set it to match your actual hardware configuration for the most accurate behavior.

Quick Reference

Metric	Good	Marginal	Poor
Total RMS	< 1.0”	1.0-2.0”	> 2.0”
Guide star SNR	> 15	10-15	< 10
RA aggressiveness	70-80%	—	—
Dec aggressiveness	60-70%	—	—
Dither distance	3-5 px	—	—
Settle time	10-15s	—	—