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Automatic filter changes in a 300g wheel for small-sensor mono cameras
Why we like the ZWO EFW 5x1.25" (2025):
- Small and light: at 120mm across and 300g (0.7lb), it's ZWO's most compact wheel, so it adds little weight or bulk to a small refractor or a light mount.
- Enough slots to start: five positions hold LRGB plus one narrowband filter, or hydrogen-alpha, OIII and SII with luminance and one spare.
- One USB-C cable: it draws only 120mA at 5V, runs from the USB hub on a ZWO cooled camera, and needs no driver. The 2025 body adds light-leak sealing and a fully enclosed motor.
- Worth knowing: if you'll want LRGB and SHO loaded at the same time, the EFW 8x1.25" holds all seven with one slot spare.
The ZWO 5-Position Electronic Filter Wheel (EFW 5x1.25", 2025 model) holds five 1.25-inch mounted filters, or 31mm round unmounted filters, and turns them into place on command from your capture software. ZWO calls it the EFW Mini. It suits mono cameras with small and mid-size sensors, like the ZWO ASI533MM Pro, ASI585MM and ASI174MM Mini. The CNC-machined aluminum body is 20mm thick and 120mm across, weighs 300g (0.7lb), and connects over USB-C to an ASIAIR, a computer running ASCOM software, or ZWO's ASIStudio.
Key specs: 5 positions for 1.25" mounted or 31mm unmounted filters · 20mm optical thickness · M42 × 0.75 threads on both sides · USB-C, 5V at 120mA · driver-free, works with ASIAIR, ASCOM and ASIStudio · anti light-leak sealing · 300g (0.7lb)
What you can image with it
- LRGB galaxies plus one narrowband layer: the Whirlpool (M51), Pinwheel (M101) and Leo Triplet in color, with the fifth slot holding hydrogen-alpha for star-forming regions.
- Narrowband nebulae from the city: Ha, OIII and SII on the Eagle (M16), Crescent (NGC 6888) and Bubble (NGC 7635), with luminance and one slot spare for RGB star color later.
- Planetary nebulae and small targets: the Ring (M57), Dumbbell (M27) and Cat's Eye suit the small sensors these filters are made for.
- Moonlit nights: an automated sequence can shoot narrowband while the Moon is up and switch to broadband after it sets.
How it works
Thread the wheel onto your camera's M42 front, add your spacers and connect it to the telescope's flattener or reducer, then plug its USB-C cable into the camera's USB hub. It shows up in your software with no driver to install. A high-precision stepper motor turns the 6061 aluminum carousel in either direction to the next filter, and your software refocuses and continues the sequence.
The wheel takes 20mm of the usual 55mm back focus, the same as ZWO's larger wheels. ZWO's layout for a cooled camera like the ASI533MM Pro is the camera (6.5mm with its 11mm ring removed), this wheel (20mm), the 2mm M42M-M42M adapter included with the wheel, then the 11mm and 16.5mm spacers that come with the camera. ZWO puts the total at 56mm, about 1mm more than 55mm because filter glass pushes focus back by roughly a third of its thickness.
What to add for the best results
- Optolong LRGB filters, 1.25" (4 pieces): fills four slots for color imaging. The ZWO LRGB set also comes in 1.25".
- ZWO 7nm SHO narrowband set, 1.25": hydrogen-alpha, OIII and SII. The Optolong SHO 7nm set also comes in 1.25".
- A mono camera: the ZWO ASI533MM Pro (cooled, 1-inch square sensor), ASI585MM or ASI174MM Mini.
- ZWO OAG off-axis guider with an ASI220MM Mini: guides through the main scope, which is ideal at longer focal lengths.
- ASIAIR Plus: runs multi-filter sequences with autofocus on each filter change.
- ZWO EAFN electronic focuser: corrects small focus shifts between filters automatically.
Compare ZWO filter wheels
| EFW 5x1.25" (2025) | EFW 8x1.25" (2025) | EFW 7x36mm (2025) | EFW 5x2" (2025) | |
|---|---|---|---|---|
| Positions | 5 | 8 | 7 | 5 |
| Filters | 1.25" mounted or 31mm unmounted | 1.25" mounted or 31mm unmounted | 36mm unmounted | 2" mounted or 50mm unmounted |
| Thickness | 20mm | 20mm | 20mm | 20mm |
| Wheel diameter | 120mm | 164mm | 164mm | 167mm |
| Weight | 300g | 530g | 515g | 540g |
| Sensor size | Up to about 1 inch | Up to about 1 inch | 4/3 inch and APS-C | APS-C and full frame |
| Best for | LRGB or SHO in the lightest wheel | LRGB plus SHO with small sensors | Larger sensors with lower-cost filters than 2" | APS-C and full-frame cameras |
For seven 2" filters, see the EFW 7x2", or browse all filter wheels and drawers.
What's in the box
- EFW 5x1.25" filter wheel
- USB 2.0 Type-A to USB-C cables, 0.5m and 2m
- M42M-M42M adapter
- 1.25" T nosepiece, 1.25" holder, 1.25" bracket and 1.25" cover
- Bag of 10 filter masks
- M2.5 × 6 screws (6), M2 × 4 screws (26) and M4 × 12 screws (2)
- 3 × 75mm Phillips screwdriver
Filters and the camera are sold separately.
ZWO EFW 5x1.25" FAQ
Do I need a filter wheel?
With a mono camera, yes, to shoot color. A filter wheel changes filters automatically during the night. With a color camera you usually don't; a single dual-band filter like the ZWO Duo-Band is enough.
5 or 8 positions?
Five slots hold LRGB plus one narrowband filter, or SHO plus luminance and one spare, in a wheel that's 120mm across and 300g. Eight slots hold LRGB and SHO together with one spare, so you never swap filters by hand, in a 164mm, 530g wheel at a higher price.
Will 1.25" filters work with my camera?
For sensors up to about 1 inch (roughly 18mm diagonal), yes: the ASI533MM Pro, ASI585MM, ASI678MM, ASI174MM Mini and ASI432MM all suit 1.25" filters. ZWO also lists 1.25" wheels for 4/3-inch sensors like the ASI294MM Pro, but with fast scopes the EFW 7x36mm is the safer choice. For APS-C, ZWO recommends 2" or 36mm filters because smaller ones may vignette, and for full frame only 2".
How do the filters go in?
Mounted 1.25" filters thread straight into the M28.5 cells. Unmounted 31mm filters sit in the same cells and are held with the included filter masks and small M2 screws. ZWO recommends mounted filters with a standard 2.5mm thread.
Does it need its own power supply?
No. It runs on 5V USB power, typically from the hub on a ZWO cooled camera, so only one short cable goes to the wheel.
Will it work with my software?
Yes. It works with ASIAIR, ASIStudio and any ASCOM program such as N.I.N.A., and it's plug-and-play with no driver to install.
What's new in the 2025 model?
A USB-C port replaces the old USB Type-B, the chassis and motor are sealed against light leaks, and the body has a refined laser-engraved finish.
Specifications
| Filters | |
|---|---|
| Positions | 5 |
| Supported filters | 1.25" mounted (filter area ≤7mm thick) or Ø31mm unmounted (1.5-3.5mm thick) |
| Carousel | 6061 aluminum, 100mm diameter, M28.5 × 0.6 cells |
| Optical and mechanical | |
| Optical thickness | 20mm (30mm at the electronics housing) |
| Threads | M42 × 0.75 on both sides |
| Body | CNC-machined aluminum, 120mm wheel diameter, 129mm tall |
| Weight | 300g (0.7lb) |
| Electronics | |
| Connection | USB-C (USB 2.0) |
| Power | 5V, 120mA from USB |
| Software | ASIAIR, ASIStudio, ASCOM, ZWO SDK; no driver needed |
| Model / SKU | ZWO-EFW-5x1.25-25 |