Discovery Astrophotography with ZWO ASTRO

EFW (5 x 2″/7 x 2″)


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ZWO EFW (5 x 2″or 7 x 2″)

Product weight: EFW 5 x 2″=500g / EFW 7 x 2″=650g

Power supply: USB2.0

Control Mode: ASCOM and SDK

Driver: Free of driver


The filter wheel body is CNC milled from an aircraft graded aluminum block.

Excellent craftsmanship, very thin and light with only 20mm thickness.

The core part of our EFW is the stepper motor which has reliable performance and quality that comes from NPM, Japan.

We have two specifications for EFW2”:

 2″ Thread-In Filters or 50.4mm ±0.5mm Unmounted Filters can be used 

The 2” Electronic Filter Wheel can be rotated in both counter clockwise and clockwise direction for filter selection.


There is no need of multiple cables to power this wheel up, just one USB cable does the trick. The maximum power supply of this EFW is approximately 120mAh @ 5V, which can be operated from the Cooled CCD’s USB2.0 port.

When connected to ASI6200, the distance from the filter to the sensor is about 18mm

Our 2″ RGBL filters are recommended to work with ASI6200MM Pro camera, it will offer nearly 1:1:1 RGB color balance.

Below requirements must be met while using the 2” filter from third-party.

Filters (not including the threads) must be less than 7.5mm in thickness and less than 50.8mm in diameter. Threads must be less than 2.7mm in thickness.

What’s in the box?

1. EFW2*5 or FW2*7 body
2. USB2.0 – 2m cable
3. A bag of M2.5*6 screws (6pcs/ bag)
4. A bag of filter masks for 50mm filters (7pcs/ bag)
5. Phillips screwdriver
6. A bag of M2*4 flat screws (23pcs/ bag)
7. M54M-M48F adapter
8. M54M-M42F adapter
9. Darkening ring sets(4pcs)

Specifications for the darkening sets:

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 drawing

Usage guide:

5 connection methods of ASI6200 to get 55mm back focus length:

[ASI6200 Guide] 5 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.

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.




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EFW (5 x 2″/7 x 2″)