Actual Step

Manual Focus Main Camera on ASIAIR Pro

updated: 2025-09-01

Purpose

Finding the correct focuser setting for best images

Previous Step

Next Step

The entire tutorial is available from ZWO Optical: How to use manual manual focusing with EAF

Required Equipment

Telescope

any

Reducer

any

Filter or Mask

Bhatinov Mask (optional)

Camera

Any ZWO ASI camera

Focuser

NONE or ZWO EAF

Session Control

ASIAIR App

Procedure:


  1. Find a bright star. Manually slew your telescope to some brighter stars, or leave the mount in the home position and use the stars near Polaris to focus.
  2. Tap the round record button in the ASIAIR app.
  3. The ASIAIR then continuously takes photos of the starry sky with this exposure time and displays them one after the other. A small square with a plus sign in the middle appears on the current image.
  4. Drag the plus sign in the green square onto a clearly visible star.
  5. Then click on the zoom tool (at the top) in the left-hand bar and the selected section will be displayed greatly enlarged.
  6. In addition, the star size (HFR - Half Flux Radius) and the Peak value are displayed. The HFR value should be as small as possible and the peak value as large as possible. 
  7. To achieve the optimum values (maximum image sharpness), the focuser must be moved in both directions using either the EAF controls or the fine tuning knob:
    1. EAF method: Use the focus controls or the hand held EAF controller to focus and fine tune on a star:
       or


  1. Monitor the HFR and peak values, and stop when optimal focus is achieved.


Additionally you can also use a Bhatinov mask to improve the focus:

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