Understanding Auto Focus

Focusing ›› Auto Focus ››
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Description: Auto focus is highly useful for keeping you in focus through the night; however, auto focus can often be difficult to understand what's going on "under the covers".  This should help to demystify those issues.  The purpose of the Auto Focus implementation in Sequence Generator Pro is to maintain focus through an imaging session.  It is not designed to handle large focus swings.  Because of this you will need to start out fairly well focused before you begin an imaging run with Auto Focus enabled.  

How Auto Focus Works

SGPro auto focus works off a notion of "whole image HFR".  Under normal circumstances, this will allow you to focus where you are imaging and avoid a costly move to a bright star and then back to target.  When auto focus is triggered, it will begin by moving the focuser "out" by ((data points * step size) / 2) steps.  It will then begin taking AF frames, averaging HFR and then moving in by "step size" until the focus point is recognized.  While "Data Points" is user defined it really only defines the number of steps used in the initial outward movement of the AF routine.  SGPro is smart enough to recognize trends and automatically extend the number of points you need in order to find proper focus (when "smart focus" is not disabled).  

In order to find the focus point SGPro will perform trend analysis (best fit lines) and use the intersection of those lines as the focus position.  When SGPro receives data that cannot provide best fit lines, it will default to using the weighted average of the lowest 3 points (this will issue a warning if you are using the notification system).

Auto Focus Variables

Unfortunately, SGPro does not have a "one size fits all" approach to auto focus and some targets will need to be tuned a bit before they can be let loose.  Fortunately, SGPro's AF routine only requires a few settings to get working properly.  The values that define auto focus are seen above and defined here.  The process by which one actually uses them to achieve focus is better described below.

So... How do you set it up for your rig?

Setup and tuning of Auto Focus should not take a long time and, fortunately, once you are able to capture a few key parameters, future adjustments can come quickly.  The first time, you use auto focus, however, all these things may seem a bit overwhelming.  This small guide should add some clarity to the process and get you going.

The general process for starting out requires the following:

Once you are setup and have your scope point at a bunch of stars, you are ready to go: