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New “XS” External Filter Wheel with 7 Positions for G2 Cameras
 While answers to many questions cannot be universally true, as it depends on who you ask, the answer to question “What is the optimal number of filter wheel positions?” is 7 for vast majority of users. Astrophotographers need Red, Green and Blue filters for true-color photography and narrow-band Hα, OIII and SII filters, plus one position for clear or luminance filter. Researchers could live with 6 positions for NUBVRI filters, but one spare position, which could be left clear, is often useful.

The reasoning above explains why the L external filter wheel for G4 cameras as well as the S external filter wheel for G3 cameras offer 7 positions. But when the same S filter wheel is used with the G2 camera, it can accommodate up to 10 (or even 12, depending on the filter size) filters. Several positions are typically left unused, but the external filter wheel is bigger and heavier than necessary. So we decided to design a new filter wheel model Ś the XS filter wheel, intended specially for G2 cameras, offering optimal 7 positions for D36ámm filters. The new filter wheel overcomes the 5-positions limit of the internal filter wheel and at the same time remains relatively compact and lightweight compared to the S model.

G2 Camera head with the XS External Filter Wheel attached

The new XS external filter wheel is intended for G2 cameras only. Its mechanical dimensions are so small, that it is not possible to attach it to the G3 or even G4 cameras. Because the wheel is designed to accommodate D36ámm unmounted filters, using of such small filters with large sensors of the G3/G4 cameras is impossible either way.

Compared to S filter wheel, the XS model is smaller and lighter

The main design goal of the XS filter wheel is the smallest physical size and lower weight for 7-positions filter wheel, but keeping the mechanical rigidity and robustness at the same time.

Even with XS external filter wheel attached, the G2 camera remains reasonably compact

The XS filter wheel remains fully software compatible, it is not necessary to update camera firmware or install new camera driver. Everything works from the start providing the camera permanent memory is properly programmed for 7 filter wheel positions.


The same XS filter wheel enclosure can accommodate a filter wheel with 8 positions for D31ámm unmounted or 1.25" filters in threaded cells. While the 8-positions filter wheel is already manufactured and tested, it requires updated drivers as no other filter wheel with 8 positions exists yet. This variant will be released with the new drivers soon.

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