Q1. What is the standard backfocus distance for ZWO cameras?

All ZWO cameras have a standard backfocus of 55mm. This matches the optical design of most flatteners and reducers. Always check your reducer/flattener manual to confirm the required distance.

Q2. How do I achieve 55mm backfocus with a ZWO cooled camera?

Start with the camera sensor to flange distance, typically 17.5mm, then add spacers and accessories to reach 55mm total. For example: 17.5mm (camera), 21mm (M42 extension ring) or filter drawer, 16.5mm (M42-M48 adapter or OAG). This gives a total of 55mm.

Q3. How do I calculate backfocus when using a ZWO filter wheel?

ZWO’s 5 Position 1.25"/31mm/36mm filter wheels and filter drawers add 20mm-21mm of backfocus.
For a typical setup: 17.5mm (camera), 20mm (filter wheel), 16.5mm (M42 extension or adapter) for a Total = 54–55mm. 

Q4. How do I set backfocus when using a ZWO OAG (Off-Axis Guider)?

The ZWO OAG adds about 16.5mm of backfocus. A sample setup might look like: 17.5mm (camera) + 16.5mm (OAG) +21mm (extension ring) Total = 55mm.

Note: The OAG prism needs to be aligned with the sensor for proper guiding.

Q5. How do filters affect backfocus with ZWO cameras?
Filters, especially in a filter drawer or wheel, shift focus slightly—typically 1/3 the thickness of the filter. For a 2mm thick filter, this means reducing the backfocus by about 0.66mm. ZWO already accounts for this in their 55mm recommendation, assuming standard filters are used.

Q6. What if my stars look distorted at the edges—could it be a backfocus issue?
Yes, coma, elongated stars, or blurry edges are common signs of incorrect backfocus. Double-check each spacer’s thickness, make sure components are properly threaded, and measure the total optical path to ensure it equals the required backfocus.

Q7. Do ZWO planetary and guide cameras require a backfocus setup?
No, uncooled ZWO planetary or guide cameras (e.g. ASI178MM, ASI662MC, ASI174MM Mini) are usually connected directly via 1.25" nosepiece and don’t require backfocus spacing unless used with optics (e.g. OAG or Barlow). They are focused by adjusting position in the focuser or OAG helical focuser.

Q8. What software can I use with my ASI camera?

The ASI Caemra range is compatible with a wide range of astrophotography software. You can use:

ZWO ASIAIR for a mobile-friendly, all-in-one imaging solution (requires ASIAIR Plus sold separtely), ZWO’s native Windows/Mac drivers with ASIStudio, third-party software such as NINA, SharpCap, APT, Sequence Generator Pro, and FireCapture, using ZWO’s ASCOM and native SDK drivers. 

Make sure your software is updated to the latest version to ensure full support for this full-frame camera.

Q9. Does the ZWO ASI Cameras  work with ASIAIR?

Yes, ASI cameras is fully supported by ASIAIR. You can control cooling (for cooled cameras), gain, offset, exposures, filters (if connected via EFW), and guiding through the ASIAIR mobile app. Be sure to keep ASIAIR firmware and the app itself updated for best compatibility.

Q10. What is the recommended gain and offset setting for the ASI cooled cameras?

This varies by target and sky conditions, but ZWO recommends:

Gain 100 for optimal dynamic range and low read noise
Gain 0 for maximum dynamic range in bright targets or longer exposures

Offset typically ranges from 30–50 but should be adjusted depending on your software and histogram.

Q11. Can I use my ASI Camera with a DSLR lens?

Yes, you may be able to use your ASI Camera with DSLR lenses using appropriate ZWO lens adapters (e.g. M54 to Canon EF/Nikon F). You will need to ensure proper backfocus and may need a manual or electronic lens controller for aperture/focus adjustments.

Q12. My software doesn't recognise my camera – what should I do?

Try the following:

• Install the latest ZWO native and ASCOM drivers.
• Check your USB 3.0 cable and port; use a powered hub if needed.
• Test connectivity with an alternative app like ASIStudio.
• Update your software or firmware (e.g. ASIAIR, NINA).