ZWO D25 UV IR-Cut Protective Window

Product Overview

The ZWO D25 UV IR-Cut Protective Window is a 25 mm replacement window for ZWO ASI cameras. It is 1.1 mm thick, figured to 1/4 λ flatness, and mounts directly in front of the sensor. It seals the sensor chamber against dust and humidity while blocking ultraviolet and infrared outside the visible band.

This is a consumable spare and a conversion part, not an upgrade to image quality on its own.

Who It's For

This is a good match if you own an ASI174-series camera — ASI174MM, ASI174MC, ASI174MM-COOL, or ASI174MC-COOL — and need to replace a scratched or contaminated window.

It is also the part ZWO specifies if you own an ASI485MC, which ships with the D25 AR window, and want to convert it to IR-cut at the sensor rather than carrying a UV/IR-cut filter in the imaging train.

Key Features & Design

• 25 mm diameter, 1.1 mm thick: the D25 form factor used on ASI174-series and ASI485MC bodies
• UV IR-cut coating: passes visible light and rejects ultraviolet and infrared, unlike the AR window, which passes both
• 1/4 λ flatness: the window sits in a converging beam directly ahead of the sensor, so surface figure feeds straight into star shapes
• Dust and humidity seal: the window is the sensor chamber's only physical barrier
• Coated optical glass, supplied as a bare window

Recommended Uses

• Replacing a scratched or contaminated window on any ASI174-series camera
• Converting an ASI485MC from AR to IR-cut, which is ZWO's own stated use for this part
• Planetary and lunar imaging through refractors, where uncorrected infrared focuses at a different point than visible light and softens detail
• One-shot-colour imaging with no filter in the train, where infrared leakage shifts colour and bloats stars

Compatibility and Accessory Notes

• Cameras shipped with this window: ASI174MM, ASI174MC, ASI174MM-COOL, and ASI174MC-COOL
• ASI485MC conversion: the ASI485MC ships with the D25 AR window; ZWO names the D25IR-CUT as the correct IR-cut replacement for it
• Diameter is not interchangeable: D25 fits 25 mm bodies only. Smaller planetary bodies take the D21; ASI1600 / ASI294 / ASI183 / ASI533 take the D32; ASI6200 / ASI2400 / ASI2600 take the D60
• No installation direction: ZWO confirms the window has no preferred orientation
• Replacement procedure: see ZWO's official guide, How to Replace the Camera Protective Window
• Mechanical part only — no electronic function, no camera communication

Important Limitations

• This is a bare optical window, not a threaded filter. It only works installed inside the camera body
• Replacement means opening the sensor chamber. Dust introduced during the swap lands on or near the sensor — work in still, clean air
• It will defeat infrared imaging. If you shoot IR-pass or methane-band planetary work, this window blocks exactly the light you want. Use the D25 AR instead
• Not a light-pollution or narrowband filter — it cuts UV and IR only
• Fits 25 mm bodies only. Check your camera against the list above before ordering
• Sold as a single window. No tools, gaskets, or retaining ring included

Frequently Asked Questions

Which cameras use the D25 UV IR-cut window?

ZWO fits it to the ASI174MM, ASI174MC, ASI174MM-COOL, and ASI174MC-COOL. It is also the specified IR-cut conversion window for the ASI485MC.

I have an ASI485MC — is this the right part?

Yes, if you want IR-cut at the sensor. The ASI485MC ships with the D25 AR window, and ZWO names the D25IR-CUT as its IR-cut replacement.

What is the difference between the AR window and the UV IR-cut window?

The AR window is anti-reflective coated but optically clear and passes UV and IR. This one blocks both. ZWO confirms the AR window does not cut UV.

Do I still need a UV/IR-cut filter in my imaging train?

Not for that purpose. With this window installed the IR-cut happens at the sensor, which frees a filter drawer or wheel slot.

Does the window have to face a particular direction?

No. ZWO confirms there is no specific installation direction.

Can I still do infrared planetary imaging with this fitted?

No — that is the one thing it rules out. An IR-pass or methane-band filter needs infrared to reach the sensor, and this window stops it. Keep or fit the D25 AR for that work.

Will this fit my ASI1600 or ASI294?

No. Those bodies use the 32 mm D32 window. This is 25 mm.

Is this good for beginners?

The part is simple, but fitting it means opening the sensor chamber. If you are not confident working clean, have it done rather than risk dust on the sensor.

Bottom Line

In short: a 25 mm × 1.1 mm UV IR-cut window at 1/4 λ flatness — the correct spare for the ASI174 series and ZWO's specified IR-cut conversion for the ASI485MC. It rules out infrared imaging by design; if you need that, use the D25 AR.