GSO 50mm Extension Tube for RC Focusers (10″+)
GSO RC telescopes have a notably long back focus distance. This makes them an excellent platform for off-axis guiders and focal reducers. In practice, however, it creates one specific problem: the focuser must be extended almost to its limit during normal use - and even then, it is often not enough. A fully extended focuser acts as a lever. This puts unwanted stress on the entire optical train and can lead to flex or vibration.
The GSO extension tube mounts between the telescope body and the focuser. It shifts the entire optical train physically into the correct position. The focuser then works within the optimal part of its travel range. No extreme extension is needed, and full mechanical stability is maintained. The result is a larger clear aperture and a stiffer, more predictable system - particularly during long exposures or when using heavier accessories such as cameras with filter wheels.
Who is this extension tube for?
This solution is especially valued by astrophotographers who need a reliable and repeatable mechanical foundation for every imaging session. Instead of improvised extensions with unstable adapters, you get a solid, precisely machined component designed specifically for this type of optics. The M117x1 thread provides a firm, centred connection with no play - exactly what large-aperture RC systems require.
Compatibility
The tube is designed for GSO and Officina Stellare RC telescopes from 10″ aperture upwards. The M117x1 thread is present on both sides - female on the telescope side, male on the camera side. This allows direct integration into the standard optical train without additional adapters. The 50mm optical length is carefully chosen to move the focuser into its optimal working position.
Key benefits at a glance
- Moves the focuser into its optimal working range
- Eliminates the need for extreme focuser extension
- Reduces flex and vibration in the optical train
- Improves stability when using heavy cameras or filter wheels
- M117x1 thread on both sides - no extra adapters needed
- Compatible with GSO and Officina Stellare RC telescopes from 10″ upwards
- Precisely machined for a firm, centred, play-free connection
Technical specifications
| Parameter |
Value |
| Optical length |
50 mm |
| Thread type |
M117x1 |
| Telescope-side thread |
Female (M117x1) |
| Camera-side thread |
Male (M117x1) |
| Compatible telescopes |
GSO RC, Officina Stellare RC (10″ and above) |
Why use an extension tube on an RC telescope?
RC telescopes are optimised for astrophotography. Their long back focus distance gives you flexibility when adding accessories. But when the focuser has to travel too far from its neutral position, stability suffers. A 50mm extension tube solves this directly - it corrects the working position of the focuser without any optical compromise. The result is a more robust setup that behaves consistently from one session to the next.
If you use an off-axis guider, a focal reducer, or a camera with a filter wheel on your GSO or Officina Stellare RC telescope, this extension tube is one of the simplest and most effective upgrades you can make to your imaging setup.
