ZWO EAF Electronic Focuser Review

ZWO – EAF 5v focuser

ZWO – EAF 5V (Electronic Automatic Focuser)

$199 as of the time of this review (accessories sold separately). See current price

Price $248 with accessories See current price

Manufacturer: ZWO


When is comes to astrophotography equipment and achieving the best images, experienced astrophotographers know that precise telescope focusing is critical. You could spend an entire night taking slightly out-of-focus images only to discover that even small errors in focusing can result in very poor image quality. Manual focusing can be tricky since moving the focuser with your fingers can cause vibrations or “rocking” in the equipment, making perfect focus look slightly blurred until the vibrations settle down. One of the most useful telescope accessories is an automatic focuser. Electronic focusers can make very fine adjustments to focus without causing these vibrations. And importantly, the position of the focuser can be digitally recorded, making it possible to return the focuser to the exact same position if necessary. The technology of electronic focusers can vary. Some focusers can be inserted into the image train and move the camera in and out to achieve focus without actually adjusting the telescope’s focuser. The ZWO – EAF telescope focuser works differently. It actually attaches to the base of the telescope and turns the focuser in tiny increments to achieve focus while the image is observed either visually or with software analysis.

The beauty of this technology is that it is possible to achieve focus automatically without intervention. Some very powerful software is available (some free) that makes it feasible to just start the software focus routine and achieve near perfect focus in a matter of minutes, even better than visual adjustments could do. Without getting too technical, the software makes small adjustments, takes an image, and compares the diameter of the star images until they are as small as possible.

In Practice

A very simple installation is performed by removing the focus knob of the telescope, inserting the spindle of the telescope focuser into the ZWO – EAF, and then mounting the device to the telescope bases. Mounting hardware is included. This result in a very stable and rigid connection. It should be noted that once the ZWO – EAF is attached, manual focus will not be possible. This is actually a good thing, because you don’t want the focus to change or slip while moving the telescope.

The unit is powered by USB, making a separate power source unnecessary. I pair the focuser with free N.I.N.A software and allow the autofocus routine to work its magic. You can even have the software evaluate the focus periodically as the temperature drops overnight and make whatever adjustments are necessary to keep perfect focus during the entire imaging session.


  1. Highly integrated design
  2. Supports ASCOM platform and various ASCOM-compatible third-party software
  3. Supports INDI
  4. Supports original software such as ASIAIR and ASIStudio
  5. Supports automatic focusing for DSO imaging
  6. Supports handle controller and manual focusing
  7. Supports temperature sensor
  8. USB HID device and driver-free
  9. Stable and durable


  • Affordable
  • Makes one-touch focusing possible without further intervention
  • Mounting hardware included
  • No additional power source required
  • Responds to industry standard ASCOM commands


  • May not fit your telescope. Check with manufacturer for compatability
  • Calibration is necessary to achieve the best and most reproducible focus



For a truly automated imaging session, an electronic focuser is a necessity. ZWO is known for producing very high quality astrophotography gear at a very reasonable price. With about a year’s worth of use, this unit has worked flawlessly for me, making long imaging sessions possible without much intervention .

Leave a Comment