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Starlight Xpress Large Format Active Optics Guiding System with OAG - SXV-AO-LF

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Starlight Xpress AO-LF Adaptive Optics

The Starlight Xpress SXV-AOLF Large Format Adaptive Optics Guiding System provides an effective method of removing the effects of rapid guiding errors from CCD images. All but the most expensive telescope mounts suffer from rapid gear errors during guiding, and such errors are very difficult to correct when the only control method available is to send speed corrections to the drive motors. A device, such as the SXV-AOLF, can adjust the image position by rapidly deviating the optical path, correcting for such errors very quickly and without the associated settling time issues.

The most common method of shifting an image for AO purposes is to use a ‘tip-tilt’ mirror to reflect the beam through a variable angle. This works well, but deviates the optical path through 90 degrees and takes up a considerable back focal distance. Its motion sensitivity is also affected by the distance between the mirror and the CCD. A ‘straight though’ device is more convenient and optically shorter, and so the Starlight Xpress AO-LF was designed with this in mind. A secondary advantage of the straight through design is that it is possible to construct a system that has a well defined optical deviation for a defined input signal. This means that the ‘sensitivity’ of the system in pixels shift per input step is essentially constant and is independent of the optical system used and the distance between the CCD and AO.

The AO element of the SX adaptive optics system is a multi-coated AR-bloomed plane-parallel optical window with a thickness of 13mm and a diameter of 60mm. This element can be tilted up to approximately +/- 3 degrees by rotating four small stepper motors at the periphery of the aluminum carrier plate. Converging light from the telescope objective lens or mirror passes through the window on its way to the CCD chip, but is essentially unaffected when the window is perpendicular to the beam. However, when the window is tilted, the converging beam is displaced by an amount which can be defined as approximately 0.075mm per 1 degree of tilt. The maximum image deviation is therefore approximately +/- 0.15mm in both the X and Y planes. This corresponds to about +/- 23 pixels on the CCD of an SXV-H9 camera.

The AO unit is usually controlled by serial data from an RS232 port. This port can be one of those provided on most PCs, or the serial interface of an SXV camera (if supported by the software package in use). A USB to serial adaptor can also be used on a PC without native serial ports. The serial data input of the AO is an RJ11 socket and so a lead with an RJ11 to 9 pin ‘D’ style socket is provided to enable connection to a standard serial port. The computer port should be set to 9600B, 8 bits data, 1 stop bit, no parity.

Features of the SX Adaptive Optics System

  • The SXV-AO-LF offers image tracking and stabilization using a high speed tip-tilt optical window.
  • Fast tracking speed of 5mS per increment.
  • Overcomes rapid gear errors to stabilize even difficult mounts.
  • Mount control output for correcting large drive errors while maintaining AO stabilization.
  • Image shift factor independent of optical system or camera back-focus spacing.
  • Off-axis guider assembly (optional) for use with an SXV guide camera.
  • STAR2000 guiding compatible.
  • May be used to image stabilize many other camera makes and types, given suitable control software.
  • Clear aperture of 60 mm for up to 35 mm 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.
  • Serial RS232 control via the computer or SXV splitter box. Parallel control available.
  • Low power consumption. Less than 600 mA at 12v DC when moving - 50mA quiescent current
  • Compact and lightweight - only 5.19 inches in diameter x 1.26 inches long - less than 2 pounds (1.54) load on the telescope.

The Starlight Xpress SXV-AOLF should be used with the off-axis guider assembly for the best results with most optical systems. This combination uses an SXV guide head or Lodestar to view the edge of the telescope field via a 10mm square prism and provides accurate positional feedback to the control software. Unlike cameras with an integrated guider chip, the OAG puts the guide camera ahead of any filters that the user fits into the camera ring recess and so its sensitivity is always at maximum. The guide camera mounting is designed to be parfocal with an SX camera when used in this combination - fine focus adjustment is provided by moving the threaded guider mount along the prism tube. If you do not need the OAG barrel (e.g. when using a camera with a built-in OAG or guide chip, such as a QSI WSG)), you can fit the 72mm or T adaptor directly onto the rear of the AO assembly.