New Version ZWO EFW 7 x 36mm



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Product Description

The new 36mm EFW (Electronic Filter Wheel) independently developed by ZWO for astronomical mono cameras. With the larger body and the newly-added screw holes on the covers, it will give a much easier and more fixable way to connect to ASI cameras.

There are 7 slots inside the EFW and we recommend you use the ZWO 36mm LRGB and SHO filter set with it.


The body is CNC milled from an aircraft graded aluminum block. It is made with high quality and thin with the thickness of only 20mm. The heart of the EFW uses the quality stepmotors produced by NPM, Japan, which can be very trustworthy. When photographing, you can rotate the EFW in both counter clockwise or clockwise direction for filter selection. The whole operation process is rather convenient and efficient.


Comparing to the original 36mm EFW, you may find the new EFW has a bigger size. The screw holes on the front and back covers shall not only allow us directly connecting the 36mm EFW to the camera and bringing the filters closer to the camera sensor, also making the it possible to match it with M68 OAG.


There are no need for multiple cables to power this filter wheel up, just one USB cable does the trick. The power consumption of this EFW is approximately 120mAh @5V, which can be operated from the Cooled CMOS’s USB hub.


All ZWO 36mm filters can be perfectly supported by this EFW. But if you use filters from third party, then please make sure the thickness of the filter should be between 1.5mm and 3.0mm (the thickness of the filter frame is 1.8mm).

What’s in the box?


Specifications for the darkening sets(4pcs):

External diameter: 88mm. Inner diameter: 55mm (2pcs) & 58mm (2pcs). Thickness: ≤0.2. 4pcs in total.
* The reason for including the darkening sets is to help solve the light leaking issue occurring in the gap of the filter wheel and camera.

How to install the darkening sets: 

Mechanical diagram


The best solution of 55mm back focus length

The latest connection methods for the new 36mm EFW and ASI cameras can be find here: The best solution of 55mm back focus length.

If you are using ASI2600, then directly head over to this instruction: [ASI2600 Guide] 4 Connection methods to get 55mm back focus length.


Q & A

1. My EFW tries to move but gets stuck and cannot arrive at the right position.

1) Filter is too thick: Filters (not including the threads) must be less than 7mm in thickness and threadsmust be less than 3mm in thickness.

2) The M2 screw used to secure the filter is too long and causes the wheel to jam.

3) The M42 thread of the scope or the camera is too long and protrudes into the filter wheel, hitting the filter or wheel, causing it to jam.

2. My EFW spins but never stops, or stops at the wrong position.

ZWO EFW uses an infrared sensor to check wheel position.  If the sensor malfunctions, you can usually resolve by recalibrating the EFW in the ASCOM driver. Simply click “ReCalibrate” in ASCOM driver interface. It can take up to 60 seconds to perform this action.

ASCOM Driver

3. I use 7-position EFW, normally I had slots 1, 2, 3, 4 filled and slots 5, 6, 7 empty, but then I got the error below and the EFW stopped working. I checked the carousel. It was not too tight or loose.


When using the filter wheel it is very important to keep its internal balance. The weight and distribution of the filters will affect balance. Thus we recommend you space the filters out and evenly distribute them. In this case, install them in slots 1, 3, 5 and 7, then the EFW will work again.