Roues à filtres

Choosing a Filter Wheel

Three specifications determine whether a wheel works in your system: filter size and count, optical thickness, and how it integrates with your camera and guider.

• Filter size and position count: More positions means fewer swaps, but a larger wheel diameter and often greater thickness. Five to seven positions covers LRGB plus narrowband for most imagers.
• Optical thickness: The wheel consumes back-focus, and this must be included in your corrector spacing calculation. Slim designs exist specifically to conserve it.
• Mounted versus unmounted filters: Wheels are built for one or the other. Unmounted square filters maximize clear aperture for large sensors but need a compatible carrier.
• Motorized versus manual: Motorized wheels are essential for unattended sequences. Manual wheels are cheaper and adequate if you are present and refocusing anyway.
• Off-axis guider integration: Many wheels accept an integrated off-axis guider, keeping the train short and the guide star picked off ahead of the filters.
• Vignetting geometry: Filter size must suit sensor diagonal and the distance from filter to sensor. Too small and the corners darken regardless of the optics.

Why Choose David Astro for Filter Wheels

A filter wheel is a back-focus decision as much as a convenience one.

• Thickness included in the calculation: We provide a complete spacing list with the wheel accounted for, so your corrector still lands on its design distance.
• Filter size verified against your sensor: We calculate the size needed to avoid vignetting rather than assuming the nominal match is adequate.
• Off-axis guider planned together: If you will need one at your focal length, we specify it with the wheel so the geometry works out the first time.
• Authorized dealer: Genuine wheels with manufacturer warranty, in Canadian stock.
• Ships from Canada: No duties or brokerage fees for Canadian orders.

Filter Wheels in Canada — Frequently Asked Questions

How many filter positions do I need?

Five covers LRGB plus one narrowband. Seven covers LRGB plus Ha, OIII and SII, which is the complete common set and avoids ever swapping filters by hand.

What filter size should I use?

It depends on sensor diagonal and how far the filter sits from the sensor. 36 mm typically suits APS-C in a standard wheel; full frame usually needs 50 mm square or unmounted 2 inch.

Does the wheel affect my back-focus?

Yes, significantly — often 20 mm or more of the typical 55 mm budget. It must be included in the calculation along with the camera and any off-axis guider.

Manual or motorized?

Motorized if you run unattended sequences, which is most of the point of monochrome imaging. Manual is a reasonable economy only if you are at the telescope throughout the session.

Building a mono imaging train?

Send us your camera, filters and corrector and we will specify the wheel and spacing. Full warranty, shipped from Canada.