Astronomy Specialist

ZWO EFW 8 x 1.25" / 31mm



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The ZWO Electronic Filter Wheel weighs only 400 grams, it is CNC machined and the optical thickness is only 20mm. This model can take 8 x 1.25″ mounted or 31mm unmounted filters.

The power absorption of the EFW is only 120mAh @ 5V so any USB cable can power it up.

The distance between the filter and sensor of the Pro cameras like the ASI1600 is circa 10mm. This close distance prevents any vignetting with 1.25″ filters for telescopes up to f/5. For f/2 lenses/telescopes it is necessary to use 31mm filters.


How to install the filters?

The EFW fits 1.25″ filters with a maximum thickness of 7mm + 3mm for the thread. To install 1.25" filters:

  1. Take the back cover off
  2. Lay the wheel down flat
  3. Screw on the filters
  4. Put the back cover on

To install 31mm and 36mm filters:

  1. Take the back cover off
  2. Lay the wheel down flat
  3. Hold the filters by the very edges and lay them on the filter wheel slots
  4. Lock each filter with a "mask" and a set of M2 screws
  5. Put the cover back on

To use the filter wheel:

  1. Install the ASCOM driver on your computer
  2. Plug in the USB2.0 cable
  3. On the Ascom options, select ZWO filter wheel (1) or ZWO Filter Wheel (2). There are two options to allow 2 filter wheels at the same time. 

How to connect with the camera and telescope?


  1. 8 x 1.25" / 31mm EFW body
  2. 1.25″ cover
  3. T2 nosepiece
  4. 1.25″ holder (with cover and 2 screws)
  5. T2-T2 adapter (male)
  6. Filter masks
  7. USB 2.0 cable (2m)
  8. Phillips head screwdriver
  9. M2 screws




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