£875.00 excluding VAT

SXV-AO-USB-NOAG ‘Active Optics’

SKU: 140-0003 Category:


The SXV-AO-USB is the 3rd generation of Active Optics from Starlight Xpress. The original design has been further developed for use with larger imaging sensors and with USB connectivity, future proofing the design further. 

The patented principle uses the refractive index of the optical window to move the incoming light path from the telescope on to the main imaging sensor. When combined with a sensitive guide camera, like the Lodestar PRO, you have a high performance tracking system that is far superior compared to autoguiding on its own. Mount correction is also included so the system is self contained and can run all night, even if there is drift due to poor alignment on the mount.

The guide camera images a star through an off-axis guider (OAG), either supplied with the AO Unit as an optional extra, or through an OAG built into a filter wheel such as the MIDI or MAXI filter wheels from SX. The software calculates the centroid of the guide star rapidly and accurately, and if the guide star moves, the optical window can be adjusted to compensate for the movement of the guide star. As the guide camera and imaging camera are looking through the same optical system, any corrections made for the guide star are automatically translated through to the main imaging camera. 

The optical corrections are controlled by 4 stepper motors, so the small amount of movement, combined with the lightweight mass of the optical window, allows the corrections to be implemented very quickly and much more accurately than the mount drive system is capable of achieving. 

Ideally suited to longer focal lengths optical systems, the benefits of the Active Optics on the final image can also be seen with shorter focal length systems on less accurate mounts.

  • Image tracking and stabilisation using a high speed tip-tilt optical window.
  • Fast tracking speed of 5mS per increment.
  • Overcomes rapid gear errors to stabilise even difficult mounts.
  • Mount control output for correcting large drive errors while maintaining AO stabilisation.
  • Image shift factor independent of optical system or camera back-focus spacing.
  • May be used to image stabilise many other makes and types of camera, given suitable control software.



  • Clear aperture of 60mm for up to 35mm full-frame size chips.
  • Short optical length – 74mm with OAG, 44mm without (add 6mm if front end adaptor is used).
  • Very low light loss (~2%) from the multicoated optics.
  • Filter threads for adding 48mm narrow band. IR blocking or pollution rejection filters without affecting the guide camera sensitivity.
  • USB or Serial RS232 control via the computer.
  • Low power consumption. Less than 600 mA at 12v DC when moving – 50mA quiescent current.
  • Compact and lightweight – only 132mm in diameter x 44mm long – less than 700 grams load on the ‘scope.
    The SXV-AO-USB should be used with the off-axis guider assembly for the best results with most optical systems.

This non-OAG (off-axis guider) version of the SXV-AO-USB is designed to work with either a filter wheel with a built in OAG such as the MIDI filter wheel or MAXI filter wheel or a main imaging camera that has a built in OAG.

Combine this with the incredibly sensitive Lodestar PRO or Ultrastar PRO auto guide cameras, finding a guide star and tracking through the Active Optics system works absolutely seamlessly.


Some examples of the AO in use.

No processing was applied, other than cropping, so that the images are essentially ‘raw’. The mount used was a Celestron CI700 with a C11 SCT at F10

A 2x enlarged clip from an SXV-H9 image. Ten minutes with a C11 at F10 using mount guiding only.

Another clip taken a few minutes later with the AO switched on and operating at 3 updates per second.

Here are some ‘extreme’ images from an Ultima 2000 on a fork mount with poor polar alignment and rapid gear errors. The camera was an SXV-M8C and the images have been resampled to 50% of full size for display.

Without AO correction.

With the AO switched on. (The short coloured spikes on the bright stars were produced when the AO switched off for image download)


WARNING – this version of the update is applicable to ONLY older versions of the AO unit (pre-USB input). DO NOT load the update into a USB version or it will become unusable!! The warning in PHD2 should be ignored.

If you have the older serial port AO unit, download the serial port  SXV-AO utility & firmware version 120.

If you have a new USB AO unit that needs programming, please download the current USB AO utility and firmware version version 201.

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