Triggering Focus using History Metrics
The other triggers available for auto focus are relatively self-explanatory and are described here. This focus trigger, however, deserves a small explainer so that, if you want to use it, you can understand its limitations. At face value, this trigger seems ideal and, in certain cases can actually be beneficial. That said, you should understand that, in certain conditions, it may result in triggering focus runs when they are not required. Read on to understand when and why this may happen.
HFR Trigger for Auto Focus
The trigger settings:
The top-level “on / off” setting… worded “Auto focus as Image History degrades”. There are more settings to be found for this trigger by clicking on the gear icon.
Why is there a little warning icon next to this trigger?
This trigger may result in unnecessary focus runs. Even in perfect focus, the HFR metric for your light frames will degrade naturally when the target is on the West. SGPro is not able to differentiate this normal degradation from actual poor focus and it is possible to trigger auto focus more often than needed. As such, if you will be running auto focus on the West over a significant drop in altitude, you may want to consider allowing this trigger to be active on the East only (click the setting icon to the right).
Here are the trigger settings:
You can also enable or disable the trigger from here. Hopefully self explanatory-ish. Choose a degradation threshold as a percent of your “in-focus” marker (reference), then choose how to average those numbers in order to avoid focus runs triggered by outliers. Finally, you can choose to use one of 4 metric combinations as input to the trigger:
- HFR and Star Count
- HFR or Star Count
- HFR Only
- Star Count Only
Finally, the 2 options at the bottom:
- Disable trigger when target is in the West. As explained above.
- Trigger focus when baseline reference is missing. In order for this trigger to function, there must be a reference frame. Any auto focus run from any any trigger can produce this baseline reference so it may come from a different trigger. In the case where no other trigger has caused auto focus, this trigger will run auto focus in order to establish the baseline.
Note: Every Event has (needs) its own baseline reference
You can check on the current baseline reference for this trigger:
- In the Image History graph. If you are viewing the history graph for an event where at least one focus run has completed successfully, the baseline history mark will be notated.
- In the Focus Module. The Focus Module will display the baseline focus metrics for the current event (if they exist)
- In Event Settings. The Event's Settings will display its own Image History graph that shows history for that event only. If at least one focus run has completed successfully during the execution of this event, the baseline history mark will be notated.
Here is an example baseline marker as shown in Event Settings: