ZWO 7-Position 36mm Electronic Filter Wheel (EFW 7x36mm, 2025)

Seven filters big enough for 4/3-inch and APS-C sensors, at a lower cost than 2"

The ZWO 7-Position Electronic Filter Wheel (EFW 7x36mm, 2025 model) holds seven 36mm round unmounted filters and turns them into place on command from your capture software. It's the wheel we suggest for mono cameras with 4/3-inch and APS-C sensors, like the ZWO ASI294MM Pro and ASI2600MM Pro, when you'd rather not pay for 2" filters. The CNC-machined aluminum body is 20mm thick and 164mm across, weighs 515g (1.1lb), and connects over USB-C to an ASIAIR, a computer running ASCOM software, or ZWO's ASIStudio.

Key specs: 7 positions for Ø36mm unmounted filters, 1.9-3.5mm thick · 34mm clear opening per cell · 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 · 515g (1.1lb)

What you can image with it

• Wide nebula fields in SHO: hydrogen-alpha, OIII and SII on the Heart and Soul, the North America and Pelican, the Veil and IC 1396, framed with the extra width of a 4/3-inch or APS-C sensor.
• Galaxies and clusters in LRGB: Andromeda (M31), the Triangulum Galaxy (M33), the Pleiades and the Leo Triplet, with luminance for detail and RGB for color.
• Mixed targets in one season: galaxies with an Ha layer to bring out star-forming regions, or nebulae with RGB stars, without opening the wheel.
• Every kind of night: an automated sequence can shoot narrowband while the Moon is up and switch to broadband after it sets.

How it works

Drop each 36mm filter into its cell and hold it with one of the included filter masks and its small M2 screws. Thread the wheel onto your camera's M42 front, add spacers to reach your flattener or reducer, and 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. ZWO's 55mm guide uses the same layout for 36mm, 31mm and 1.25" wheels on 4/3-inch and 1-inch cooled cameras: for an ASI294MM Pro that's 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, for a total of 56mm. The extra millimeter allows for the filter glass, which pushes focus back by roughly a third of its thickness. An APS-C camera like the ASI2600MM Pro uses 12.5mm, so camera plus wheel come to 32.5mm and the rest goes to spacers or an off-axis guider.

What to add for the best results

• Optolong LRGB filters, 36mm unmounted (4 pieces): fills four slots for color imaging.
• Optolong SHO 7nm set, 36mm unmounted: hydrogen-alpha, OIII and SII for the last three slots.
• A mono camera: the ZWO ASI294MM Pro (4/3-inch) or ASI2600MM Pro (APS-C).
• 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

For the lightest 1.25" wheel, see the EFW 5x1.25", or browse all filter wheels and drawers.

What's in the box

• EFW 7x36mm 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 7x36mm 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.

36mm or 2" filters?

ZWO recommends 2" or 36mm filters for APS-C cameras and only 2" for full frame. 36mm is the lower-cost choice for 4/3-inch and APS-C sensors; at very fast focal ratios an APS-C sensor may show slight corner darkening, which flat frames correct. If you might move to a full-frame camera later, 2" filters and the EFW 7x2" will carry over.

Can I use mounted (threaded) filters?

No. The cells take 36mm round unmounted filters from 1.9 to 3.5mm thick. For threaded 1.25" filters, see the EFW 8x1.25"; for threaded 2" filters, the EFW 5x2" or 7x2".

Will it work with my camera?

It suits mono cameras with 4/3-inch sensors such as the ASI294MM Pro (23.2mm diagonal) and APS-C sensors such as the ASI2600MM Pro (28.3mm diagonal). It also works with smaller sensors, though 1.25" filters cost less for those.

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