Hello fellow Ekos users,

Differential phabricator.kde.org/D18510 presents a tweak to the Full Field focusing method. It is available in the Focus tab as two percentage edit boxes when option "Full Field" is enabled.
With the default percentage values 0%/100%, the original full-field focusing procedure consolidates the mean HFR of stars detected in the whole frame.
With any other percentage values, the focusing procedure only considers stars located in a ring surface defined by the inner/outer percentages of the largest dimension of the frame.

The Full-Field and Ring-Field methods require more system resources and are generally slower than the subframe method.
However, they are more robust against detection of out-of-focus star agglomerations or galaxy cores because they average HFR values over more star samples.

The Ring-Field method improves focus quality compared to the Full-Field method:

• When capturing centered galaxy objects, by disregarding stars in the center of the frame.
• When the optical field is not flat enough and produces elongated stars on frame borders, by disregarding stars in the outer part of the frame.

The Ring-Field method also offers better control on which part of the frame to focus on.

Note that Jasem added further fixes to the differential code shown at phabricator.kde.org/D18510.

SUMMARY

Adds inner and outer limits to filter stars when running a full-frame focus procedure.
When option "Full Field" is enabled in the Focus tab, the procedure will first detect stars that are visible on the frame, using either the SEP method (if selected) or the Centroid method, and remove stars not in the ring surface bounded by the inner and outer radius values before calculating the mean HFR.

TEST PLAN

Use case: execute the Full-Field focus procedure

In the focus tab, tick the checkbox "Full Field".
As a result, the "Subframe" checkbox is unticked and the two edit boxes on the right of the "Full Field" checkbox shift to the enabled state.

Those left-hand and right-hand boxes respectively define the inner and outer radii as percentages of the largest dimension of the frame (usually the width).
If needed, change those inner and outer values to the default 0% and 100% respectively.

Click button "Capture" to capture a frame from the registered CCD.
After the exposure duration elapses and data is downloaded, the frame appears in the FITS view.

The Full-Field procedure is used to consolidate the mean HFR of detected stars in the whole frame.
The algorithm selected for detection of stars is SEP if explicit, else is Centroid. Different algorithms may pre-filter the frame differently, and as a result may consider a different amount of stars.
Stars considered for HFR calculation are marked in red on the FITS view if the "Detect Stars in Image" overlay option is enabled.
The mean HFR resulting from the calculation is displayed at the bottom of the V-Curve under the FITS view.

If your setup has an automated focuser, click the button "Auto Focus" to automatically iterate the procedure with the same settings until a minimal HFR value is obtained.
Alternately, adjust the focus manually on your setup, and click the button "Capture" again to continue the procedure with the same settings.
Alternately, click the button "Framing" to repeatedly execute the procedure with the same settings while you adjust the focus manually.

Use case: execute the Ring-Field focus procedure

In the focus tab, tick the checkbox "Full Field".
As a result, the "Subframe" checkbox is unticked and the two edit boxes on the right of the "Full Field" checkbox shift to the enabled state.

The Ring-Field procedure is used to consolidate the mean HFR of detected stars in a subframe in the shape of a ring, defined by the inner and outer radii.
The left-hand and right-hand boxes respectively define the inner and outer radii as percentages of the largest dimension of the frame (usually the width).
The default inner and outer values are 0% and 100% respectively, but Ekos will remember the values last entered, even from a previous session.
Change the default values 0% and 100% to 20% and 80%. You may use any non-default percentage value you require.

Click button "Capture" to capture a frame from the registered CCD.
After the exposure duration elapses and data is downloaded, the frame appears in the FITS view.
The algorithm selected for detection of stars is SEP if explicit, else is Centroid. Different algorithms may pre-filter the frame differently, and as a result may consider a different amount of stars.
Two blue dashed circles are drawn, one for the inner radius, one for the outer radius, to help you find the best ring surface for the target you plan to capture.
Stars considered for HFR calculation are marked in red on the FITS view if the "Detect Stars in Image" overlay option is enabled, and only appear between the two blue circles because of the specific selection.
The mean HFR resulting from the calculation is displayed at the bottom of the V-Curve under the FITS view.

If your setup has an automated focuser, click the button "Auto Focus" to automatically iterate the procedure with the same settings until a minimal HFR value is obtained.
Alternately, adjust the focus manually on your setup, and click the button "Capture" again to continue the procedure with the same settings.
Alternately, click the button "Framing" to repeatedly execute the procedure with the same settings while you adjust the focus manually.

Use case: restore the Subframe focus method

In the focus tab, click the "Subframe" method.
As a result, the "Full Field" checkbox is unticked and the two edit boxes on its right shift to the disabled state. Note they retain their value nonetheless.

In that situation, the Full-Field and Ring-Field methods are not used when running the focus procedure.

-Eric