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ZWO EFW 8-position Filter Wheel for 1.25" Mounted and 31mm UnMounted Filters

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This electronic filter wheel from ZWO is most likely of of the smallest 8-position filter wheels in the world. It is also extremely lightweight, it weighs 400g only.

Its housing is CNC machined from aircraft grade aluminium alloy.

The stepper motor, that is the heart of any electronic filter wheel, is made by a reliable Japanese company, NPM. You can trust its quality and reliability.

This high quality 8-position filter wheel has been designed mainly for astro photography, especially, but not exclusively for ZWO ASI1600 cameras.

Depending on the focal ratio of your telescope you can use it with standard 1.25" filters in filter cell or you can choose 31mm unmounted filters where a smaller filter would cause vignetting and use of at least 31mm filters is necessary.

As it is ASCOM compatible, therefore it can be used with cameras of other brands as well.

Up to 8 filters can be installed in the numbered compartments that accepts both 1.25" (mounted) and 31mm (unmounted) filters (or semi-mounted 31mm Astronomik filters), and each can be selected for your eyepiece or camera from an imaging software.

ZWO now offers 1.25", 31mm and 36mm LRGB and narrowband deep sky filters as well.

The filter wheel can be attached to your focuser either by the supplied 1.25" nosepiece adaptor or via a T-thread. There is actually a female T-thread on both sides of the filter wheel, but it also comes with a reverse adapter with male T-thread on both sides.

The robustly constructed filter wheel is supplied with a 1.25" nosepiece and a 1.25" eyepiece holder with brass compression ring.

Please note: your focuser will require 20mm of additional inward focusing distance from the normal focus position to compensate for the thickness of the filter wheel.

This filter wheel will be a good addition to the new ASI1600 range of cameras, but especially for the monochrome versions. (please make sure that your telescope otherwise have enough back focus, of course, e.g. Newtonian telescopes would usually have a back focus issue, unless modified or specially designed for astro photograpy...)


The distance between the filter and sensor is around 10mm when you connect the ASI1600 to this EFW, so a 1.25" filter wonäó»t have vignetting with a scope with up to about  f/8-f/9.5 focal ratio (depending on the thickness of the filter) and a 31mm filter won't have vignetting up to about  f/2.8-f/3.2 lens (depending on the thickness of the filter). Please note, these figures are slightly different from ZWO's own calculations and to be checked in practice.

ZWO's new RGBL filters are recommended to use with ASI1600 cameras, as these specially designed filters will offer nearly 1:1:1 RGB color balance.

The full ZWO EFW 8 set includes:

  •     EFW 8-position filter wheel
  •     T2 nosepiece
  •     1.25" Holder-T2
  •     T2-T2 adapter
  •     USB2.0 Cable


1.25" filter requirement: threads length shorter than 3mm, height without threads less than 7mm

31mm filter requirement: a set of M2 screws and washers needed to fix the filter are included in the package
How to use it?

you just need to plugin the EFW with a USB2.0 cable and install the  ASCOM driver from here.

There are  ZWO Filter Wheel(1) and ZWO Filter Wheel(2) to select,  you can use either one of them.

You can control 2 filter wheels simultaneously from one software.


Specifications: ZWO EFW 8-position Filter Wheel for 1.25" Mounted and 31mm UnMounted Filters


  •     Limiting F-ratio: apprx f/3 with 31mm filters and f/8 with 1.25" filters (calculated with ZWO's 2mm thick filters)
  •     Thickness: 20mm
  •     Power consumption: 150 mA at 5 Volts
  •     ASCOM compatible
  •     Positions: 8 x 1.25" or 8 x 31mm glass, unmounted or semi-mounted (like Astronomik)
  •     Weight: 400g


What's in the Box

What's in the Box: ZWO EFW 8-position Filter Wheel for 1.25" Mounted and 31mm UnMounted Filters

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