Focusing

Establish sharp focus with the physical eclipse rig, prepare SharpCap Focus Assistant, and optionally let HelioMaker request one SharpCap refocus before the central phase.

Focus the Sun before you arm

Focus on the filtered Sun and confirm sharpness before you start the run. Use a clear feature, such as the limb, a sunspot, or the crisp edge of the partial crescent, and refine focus until it is as sharp as the seeing allows. Use the same telescope, camera, solar filter, optical train and motorized focuser that will image the eclipse. The preflight checklist has a Focusing gate that reflects whether you have a confirmed focus baseline.

Thermal drift Focus drifts as the tube and air cool through the partial phases. That is exactly what the automatic refocus is for. If you do not have a motorized focuser, plan to nudge focus manually during the partials and lock it well before C2. You do not want to be touching the focuser as the diamond ring appears.

Prepare SharpCap Focus Assistant first

HelioMaker does not calculate the focus curve itself. When Automatically refocus before totality is enabled, HelioMaker asks SharpCap Focus Assistant to repeat SharpCap's last successful focus scan. SharpCap saves the method and scan settings only after a successful scan, then its Refocus command reuses them. You must therefore complete at least one successful solar focus scan in SharpCap before enabling automatic refocus in the eclipse plan.

Choose a solar focus method

Contrast (Edge) Detection is the recommended starting point for the Sun. It uses surface contrast and the solar limb, and SharpCap identifies it as suitable for planetary and surface targets.
Fourier Detail Detection is a valid alternative. Try it with your own rig and use whichever of the two methods produces the most repeatable sharp focus.
Do not prepare the eclipse refocus with an FWHM, Bahtinov or other star based method. Those methods expect stellar point sources, not the solar disk, and HelioMaker will not accept a saved scan that uses one.

SharpCap Focus Assistant using Contrast Edge Detection on a
full solar disk with a motorized focuser connected. — Prepare Focus Assistant with the physical eclipse rig. Contrast (Edge) Detection is a useful starting method for the solar disk.

Configure and prove the scan

Connect the eclipse camera and motorized focuser to SharpCap, point the filtered rig at the Sun, and bring the image close to focus manually.
Open SharpCap Focus Assistant from the focus tool menu and select Contrast (Edge) Detection or Fourier Detail Detection. If a measurement area is used, make it large enough to contain the full solar disk with margin.
Open the scan options and set Scan Step Size, the focuser movement between measurements, and Max Step Count, the maximum number of those steps in the scan. SharpCap also lets you set how many samples are collected at each step.
Run a focus scan that passes through best focus and collects measurements on both sides of the peak. Adjust the step size and count until SharpCap can identify a convincing best focus position and return to it.
Inspect the solar image and confirm that the result is genuinely sharp. Then manually launch SharpCap's Refocus command at least once to confirm that it can repeat the result using the saved scan.
Only after that test succeeds, enable the automatic refocus option in HelioMaker Plan preferences. Its exact label names the phase it precedes, and so follows the eclipse type: see the list below.

SharpCap Focus Assistant scan options showing Scan Step Size,
Max Step Count and Samples to collect at each Step. — Tune Scan Step Size, Max Step Count and the sample count until the scan crosses best focus and measures both sides of the focus curve reliably.

For SharpCap's description of the focus tools and graphs, see SharpCap Focus Assistance.

A successful SharpCap focusing scan is required Enabling automatic refocus in HelioMaker does not configure SharpCap and cannot create the first focus scan. Without a previous successful SharpCap focus scan and saved solar method, automatic refocus will not work. Configure and prove SharpCap first; enable the plan option only after SharpCap can refocus the physical rig successfully.

Automatic refocus before the central phase

After SharpCap has a successful saved solar focus scan, HelioMaker can request one SharpCap refocus shortly before the central phase, so the most important frames are taken at fresh focus. It is deliberately a single operation timed a few minutes ahead, with a hard cutoff so it always finishes before the central capture window opens. On a total eclipse that cutoff is what keeps it clear of the diamond ring. Periodic refocus during the partials is intentionally not done.

This is available for every eclipse type, and the option names the phase it precedes:

total: Automatically refocus before totality
annular: Automatically refocus before the annularity phase
partial: Automatically refocus before the central phase

The wording names the phase rather than the astronomical instant on purpose, because that is what the schedule is measured against. The countdown runs back from the moment the phase begins, including whatever Start before (s): that phase carries in the Phase editor, and not from annularity or maximum itself. The reason to do it at all is the same in all three cases: the tube and the air have been cooling for an hour or more by then, and the frames you care about most are the ones after that drift.

Focusing group in Plan preferences with automatic refocus enabled,
minutes before totality and refocus timeout settings. — Enable automatic refocus only after SharpCap has saved a successful solar focusing scan and its Refocus command has been tested with the physical eclipse rig.

The refocus is guarded: it manages the focuser carefully around the scan (temperature compensation is only touched around the scan and restored afterwards, and the focuser position is supervised and repaired if needed). HelioMaker also pauses PHD2 guiding corrections during the refocus scan. This prevents small mount movements commanded by guiding from introducing jitter while SharpCap measures focus, helping the scan obtain a more accurate focus result. Guiding resumes after the scan when the current eclipse phase permits it.

Planned captures continue during refocusing Refocusing does not stop the eclipse capture schedule. If a planned exposure occurs while the focuser is moving or SharpCap is measuring the focus curve, that image may be slightly blurred. This is expected; inspect frames captured during the refocus interval during post-processing. The benefit is that the imaging sequence remains on schedule while the rig establishes a sharper focus for the more important phases that follow.

The automatic refocus runs only when all of these are true:

Automatic refocus is enabled in the plan preferences;
SharpCap has a successful saved solar focus scan using Contrast (Edge) Detection or Fourier Detail Detection;
A motorized focuser is connected in SharpCap and passes the preflight connection check;
In shared-camera mode, HelioMaker has a stable solar detection and SharpCap's saved focusing region contains the complete detected solar disk;
You have manually confirmed that SharpCap can refocus the physical eclipse rig successfully;
You have not declined it in the preflight checklist; and
The eclipse is total (refocus is available only for a total eclipse).

The preflight Focusing badge The preflight checklist has a Focusing badge that checks for a connected focuser and a successful saved solar focus scan. When automatic refocus is selected, confirming that the target is focused is not enough by itself: the badge remains red until Recheck focuser verifies the live SharpCap focuser connection and saved solar focusing method. In shared-camera mode it also checks that a stable HelioMaker detection places the complete solar disk inside SharpCap's saved focusing region. If the disk or region cannot be verified, correct the framing or the Focus Assistant region and recheck. Its three buttons are Recheck focuser, Run autofocus (request SharpCap Refocus; it turns to Cancel while running), and Do not auto refocus before totality (or before the annularity phase / before the central phase, matching the plan) to opt out. You then tick a confirmation: "I've run SharpCap focusing/refocusing successfully" when refocus is on, or "The imaging target is focused" when it is off. Run autofocus is a final confirmation shortcut, not a substitute for configuring and proving Focus Assistant in advance.

Expanded Focus and auto refocus preflight item showing confirmed
focus, refocus controls and the successful SharpCap focusing confirmation. — The preflight item confirms focus separately from the live focuser and saved-scan checks. Run autofocus repeats the prepared scan; it does not configure the first scan.

If you override the focus check If you override the focus confirmation before arming, the planned refocus will not run, and the run console shows a red warning saying refocus is "in your plan but will NOT run" so you are never misled into thinking it happened. If refocus matters to you, satisfy the focus gate rather than overriding it.

Rehearse the refocus First prove the saved scan by manually requesting Refocus in SharpCap. Then use Run autofocus in preflight and rehearse the scheduled action in a simulated run with the physical rig. You should already know that SharpCap can return to sharp focus, when the scheduled scan fires, and what the badge looks like while it works.