Question about AutoFocus @ Actual Position

I’m trying to diagnose some tilt in my setup. To collect data for this, I’m looking for a reliable way to focus in specific areas of the image frame (top left, top right, etc.) If possible, I’d like to use Voyager’s VCurve to do this.

I don’t see an obvious way to ask Voyager to focus on a subframe, but I’m wondering if I can still achieve what I want by using the “AutoFocus @ Actual Position” action under the “On The Fly” tab.

The wiki says that AutoFocus @ Actual Position uses a “suitable star” at the current scope position. How does Voyager determine the “suitable star”? Does it pick the brightest star in the field? If yes, I can just achieve what I want by moving the scope until there’s a single bright star at the position that I want to focus on.


  • Rajeev

Hello Rajeev, in Voyager you can define area % for LocalField or ROI % but only centered. When you think to Voyager you cannot think like the other automation system. Voyager use AI so … if you choose the whole frame for focus in RoboStar (percentage to 100%) the AI will choose the best star according the recognized shape and mag in his deep learning but related to center frame. I cannot predict for you where will be this place. For sure not in the corner you need.

About tilt , LocalField focus help you to flattned the field lost some performance in best FWHM.

All the best

Hi, Leo,

No worries, thank you for clarifying. I’ve written a dragscript to take a series of images, starting on one side of focus and going to the other side, and then analyzing them to find the best focus point in each corner. By keeping the focuser movement small (approx the CFZ), I can get a pretty good idea by doing that too.

And, yes, I often use LocalField for exactly the reason you suggest.

Thanks again for the clarification,


  • Rajeev