Handbook for the Starlight Xpress SXV AO unit

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005Handbook for the Starlight Xpress SXV-AO unitThank you for purchasing an SXV-AO active optics unit. This device should give youmuch improved guiding accuracy with almost any telescope and mount. Please read thefollowing manual which will explain how the device operates and the best ways in whichit can be applied to your optical system.The principle of operation:The SXV-AO device provides an effective method of removing the effects of rapidguiding errors from CCD images. All but the most expensive telescope mounts sufferfrom rapid gear errors during guiding and such errors are very difficult to correct whenthe only control method available is to send speed corrections to the drive motors. Adevice which can adjust the image position by rapidly deviating the optical path, cancorrect for such errors very quickly and without the associated settling time issues.

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005The 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 theoptical path through 90 degrees and takes up a considerable back focal distance. Itsmotion sensitivity is also affected by the distance between the mirror and the CCD. A‘straight though’ device is more convenient and optically shorter, so the SX unit wasdesigned with this in mind. A secondary advantage of the straight through design is that itis possible to construct a system that has a well defined optical deviation for a definedinput signal. This means that the ‘sensitivity’ of the system in pixels shift per input step isessentially constant and is independent of the optical system used and the distancebetween the CCD and AO.The AO element is a Multi-coated AR bloomed plane-parallel optical window with athickness of 12mm and a diameter of 40mm. This element can be tilted by up toapproximately +/- 3 degrees, by rotating four small stepper motors at the periphery of thealuminium 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 unaffectedwhen the window is perpendicular to the beam. However, when the window is tilted, theconverging beam is displaced by an amount which can be defined as approximately0.075mm 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 theCCD of an SXV-H9 camera.The AO unit is usually controlled by serial data from an RS232 port. This port can be oneof those provided on most PCs, or the serial interface of an SXV camera (if supported bythe software package in use). A USB to serial adaptor can also be used on a PC withoutnative serial ports. The serial data input of the AO is an RJ11 socket and so a lead with anRJ11 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.A typical application of the AO unit for off-axis guiding:The following diagram shows how the AO unit may be used with the optional off-axisguider (OAG) and an SX CCD camera. This is likely to be the normal configuration formost imagers, as it offers accurate guiding which is free of flexure and mirror shiftproblems. The OAG consists of a short aluminium barrel with a pick-off prism whichfeeds light to an SXV guide camera, mounted at the end of a short extension tube. Theguide camera position is designed to be close to the correct focal distance when aStarlight Xpress camera is mounted on the main optical output of the OAG and broughtinto focus. Any small errors may be corrected by loosening the two set screws in thethreaded collar and sliding the camera into the correct position.The OAG is attached to the AO unit by two set screws which engage with a grooved ringat the output of the AO assembly. Please note that the guider barrel should be oriented sothat it projects along the line which joins the North and South motors. When locatedproperly, the two RJ11 sockets on the AO will be at the bottom of the unit, diametricallyopposite to the guider barrel. The long axis of the CCD in the guide camera should be

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005oriented so that it is parallel to the AO backplate. This can be seen in the picture at thefront of this handbook, as indicated by the orientation of the guide camera socket.The imaging camera is attached to the rear of the OAG, using a suitable adaptor ring.Two types are supplied – one with a ‘T’ thread for the SXV-H9/9C and M25C and onewith an M42 thread for the rest of the SX range. The orientation of the camera is adjustedby loosening the two set screws and rotating the ring into the required position. As thecamera is not involved with collecting guiding information, it may be set at any angle.However, the pick off prism may cause shadowing if the long axis of a large chip is set inthe vertical plane.Both the AO unit and the OAG have recesses which will take a 48mm filter. When usingthe OAG, it is an advantage to use the recess inside the camera mounting ring, so that theguide camera sensitivity is not compromised by any filters that you may add. This is

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005especially useful if you image with narrow band filters, such as H-alpha. A light pollutionrejection filter, such as an IDAS P1 or P2 might be best added at the output of the AOunit, where it will improve the guide star contrast, as well as improving your cameraimages. Note that the recesses are not threaded and so you should be careful that a filterdoes not fall out and get damaged when dismantling the unit.N.B. Although the SXV-AO was designed for operation with an SX camera, it ispossible to attach other imagers with an appropriate adaptor and still use the AO via oneof our USB2 interface boxes. The USB2 interface provides a convenient way to read andcontrol the SXV guide camera, even when no SX main imager is in use. You will need toorganise the alternative camera spacing so that it may be brought to focus simultaneouslywith the guide camera.Connecting up the AO electronics for off-axis guiding:The method of connection will vary slightly, depending on the guiding software in useand the equipment available. The SX software and AstroArt allow you to use the SXVport divider box for serial control of the AO unit and so you might prefer to use thismethod to cut down on the number of cables required. At the time of writing, Maxim DLdoes not offer an option to connect via the divider box and so a serial cable from the PCCOM port will be required if you use Maxim. PCs with no COM port can use acommercially available USB to serial interface for the connection.1) Connect the serial to RJ11 cable (supplied) into the AO unit input socket.2) Connect the RJ11 to guider port cable (supplied) from the AO output to the guiderinput on the mount. This cable is not essential, but it allows the software to‘bump’ the mount when the errors become too large for the AO unit. Most lowercostmount users will find it necessary for long exposure times.3) Connect the guide camera to the socket on the SXV imaging camera, or the socketon the SXV interface box (used with older parallel port imaging cameras, or whenimaging with other makes of camera). Include the port divider box in this cable, ifyou intend to use this for serial control (Fig 1).4) Connect the serial to RJ11 cable to the appropriate port divider output, or to theRS232 cable from your PC (Fig 2).5) Connect the AO power lead to the power supply block.

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005.Fig 1Fig 2

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005Connecting up the AO electronics for STAR2000 guiding:STAR2000 guiding does not require the OAG unit and the camera may be attacheddirectly to the AO. As with off-axis guiding, there is more than one way to connect up theAO for STAR2000 use. Figure 3 shows the most likely way for most users to connect forserial control via the PC. Other alternatives include serial control via a port divider on anSXV output and parallel control from the RJ11 guider output of an SXV camera.General pointers:Fig 3When the AO unit is first attached to the telescope, it is necessary to arrange the off-axisguide camera, or the STAR2000 camera, so that the East – West AO axis is parallel to thelong axis of the guide image. This is easily done by viewing the guider or camera chipthrough the front of the AO window. Hold the AO unit so that the two RJ11 sockets areat the bottom and ensure that the guider chip is visible as a horizontal rectangle as seen inthe off-axis prism. A STAR2000 camera chip should also appear as a horizontal rectanglein this view.

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005The SXV-AO can execute an image position correction in a few milliseconds, but theeffective correction rate is limited by the brightness of the guide star and the downloadspeed of the guide camera image. For best results with a poor telescope mount, you needto choose as bright a star as possible and use a small guide window. Binning the guidecamera image will also help.The orientation of the AO assembly is normally arranged so that the East-West RA driftdirection is along the long axis of the guider chip. However, there is no reason to conformto this if the mount corrections can cope with the non-standard orientation. In this case,you can rotate the entire unit about the optical axis for optimising the image orientationor for finding a suitable guide star.When attaching the AO unit to a T thread adaptor, be careful to ensure that the malethread does not project into the AO body. Any projection can interfere with themovement of the image displacer and may jam the unit. If the thread is too long, add athin card or plastic washer between the adaptor and AO front plate.

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005During extreme movement of the displacer, the motors may encounter excessive frictionand fail to start. The ‘centre’ command will normally overcome this, as it switches to amuch lower speed, high-torque stepping rate after 5 seconds of failure to move. However,in the worst case, you can rotate the motors manually by inserting a small screwdriverthrough the holes in the front plate. Be careful not to rotate them too far, as only 4 turns isrequired to move the drive through its entire range. Adjust each motor until its shaftrotates as freely as possible before using the ‘centre’ command again.Using the AO system:The following instructions are based on the software provided by Starlight Xpress andwill be different for other control programs. Please read the relevant help files if you areusing AstroArt or Maxim DL. I also assume that you are using the off-axis guider andserial control of the AO.Open the camera software and check that it recognises the presence of your main camera.Now open the ‘Set program defaults’ menu (under ‘File’) and check that the serial controlsettings are appropriate to your system. For instance, if you are using a serial port on thePC to drive the AO unit, check the ‘AO unit available’ check box and then set the PCCOM port number. The ‘Select half rate’ box is to slow down the mount corrections thatwill occur if the AO unit exceeds its useful range. You may find this useful if you have amount with rather erratic drives, such as an SCT on a fork mount. Now save the programdefaults and return to the main program window.Select the main camera icon (4 from the left) and use a short exposure time to see if thereare any stars visible. Adjust the main telescope focus until you have a well focused starfield in the main camera image.Now click on the ‘Autoguider’ icon (5 from the left) and you will see the guider windowand control panel. Select a 1 second exposure time and move the ‘Stretch image’ slider to‘Maximum’. Press the ‘Start’ button and you should see a guide camera image appear inthe image window. At this point, there may be no stars visible, as the guider focusingmight be seriously in error. If no stars are seen, try increasing the guide exposure to 3 ormore seconds until you can detect some stars. Now use the Allen key provided to loosenthe two set screws in the guider retaining collar and then gently slide the guiderbackwards and forwards until a sharp star image is seen. Note that the image might bedistorted by the telescope optics, as it is well ‘off axis’. Once focused, re-lock the collarin place, making sure that the guide camera orientation is with the input plug parallel tothe AO backplate. Briefly blip one of the RA buttons on your telescope handset andensure that the stars drift parallel to the long axis of the guider window – if not, rotate theentire AO assembly about the telescope axis until they do so. Now check that the AOmode is set for ‘serial’ and make sure that you have selected the correct AO control portif you are using the splitter box (ser1 or ser2). Press the ‘Use default’ to temporarily setthe guiding speed of the AO. You now have the system ready to test, so proceed asfollows:

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005Find an interesting object or starfield to image and adjust the ‘scope until a convenientguide star can be seen in the guider field. Ideally, the star should be easily seen in anexposure of only 0.1 seconds and, if necessary, binning may be used to gain sensitivity.Once the guide star is identified, press the ‘Centralise AO’ button and watch the starimage – it should cycle through a cross shaped figure and then settle after about 2seconds. Now press ‘Select guide star’ and click on the star which you think best suitedto act as your guide reference (bright and isolated). You can now press the ‘Train’ buttonand the AO will cycle automatically while measuring the system sensitivity. If thetraining cycle is successful, new rate values will be generated, although they willprobably be much the same as the default values. If the calibration fails, it will probablybe due to one or both of the AO direction settings being wrong. The defaults in thesoftware are for a guide camera mounted as shown in the frontispiece picture of the AOassembly, with its indicator LED towards the camera end of the AO barrel. You caneither rotate the guide camera to this position, or try swapping the AO up/down andleft/right check box settings. Once you have the directions set and the motion ratesdetermined, calibration of the AO will not be necessary in future sessions as it is aconstant factor for all ‘scopes. Only one other setting is still necessary. This is thecalibration of the mount for ‘mount bumps’ during your guiding session. Although theAO can take care of the small and rapid guiding errors, there will be steady drifts of thetelescope drive which will slowly shift the AO to the limits of its motion range. Tocombat this effect, we need to send occasional corrections to the mount (‘bumps’) inorder that the AO remains near to the centre of its operating range. A relatively easy wayin which to determine the settings required is to set the AO guiding on your selectedguide star (press ‘Start guiding’) and then use the hand controller to move the star slightlyEast or West until the data boxes on the guider image start to show offset values of morethan 50 steps. At this point you will see the text ‘Move mount’ appear, along with adirection indication. If the result is that the AO error falls rapidly below 50 steps, then themount direction and rate is about right, but any sign that the error is rapidly increasingwill show that the ‘Swap e/w’ or n/s direction is incorrect. Stop the guiding, reverse the‘Swap’ box for that direction and try guiding again. Once you have both directions setcorrectly, you can experiment with the mount speed (pixels per second) settings tooptimise the amount of correction applied – ideally you want the mount correction tomove the AO back to the ‘zero offset’ position, but there is a large tolerance on this.You are now ready to take an AO guided image!Re-centralise the AO unit, select your guide star and then press ‘Start guiding’. Once theguide star image is stable, press the main camera icon and set your image exposure timein that dialog box. Now press ‘Take photo’ and wait for the result to appear!Updating the AO firmware:From time to time, improved versions of the AO firmware will become available and willbe posted on the Starlight Xpress web site. The AO unit is provided with a means ofupdating its internal firmware via the PC serial port. You will need the serial cable asprovided with the AO unit and this should be connected between the AO unit input

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005socket and the serial port of your PC. The updating procedure also requires the powersupply to be connected to the AO.1) Download the latest version of the updater software fromhttp://www.starlight-xpress.co.uk/SXV-AO.htm2) Uninstall any previous version of AO Updater using the Add/Remove Programs in theControl Panel.3) Install AO Updater software by executing the ‘Setup.exe’ file.4) Connect AO to a PC serial communications port (COM1 is default).5) Power up the AO unit.6) Start the AOUpdater program by clicking on the screen icon.7) If you are not using COM1 then use the Settings menu to select another COM port.8) Press the CONNECT button (if unsuccessful then refer to the HELP file).9) Press the SELECT button and OPEN the activoxxx.hex file (xxx = version number).The default directory for the hex file isC:\Program Files\Starlight Xpress\AOupdater\Hex\10) Press the UPDATE button and wait for about 60 seconds to complete theprogramming. The ‘Petrol gauge’ bar will show the state of progress. Do not open orswitch to any other applications while programming is taking place!11) Once successfully updated, exit the AO Updater program and turn the power to theAO OFF. Wait 5 seconds then switch the power back ON. The AO is now ready for use.The Active optics command set.This information is provided for users who wish to write their own control programs.The serial mode command listChar Char Char Char Char Char Char Result Return1 2 3 4 5 6 7K Find Centre KG N 0 0 0 0 1 AO 1 step North G or L(hit limit)G S 0 0 0 0 1 AO 1 step South G or L(hit limit)G T 0 0 0 0 1 AO 1 step East G or L

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005(hit limit)G W 0 0 0 0 1 AO 1 step West G or L(hit limit)M N 0 0 0 0 1 Mount 1 step N MM S 0 0 0 0 1 Mount 1 step S MM T 0 0 0 0 1 Mount 1 step E MM W 0 0 0 0 1 Mount 1 step W MRLCentre at lowspeed (unjam)Get Limit switchstatusKCharacterwith an ASCIIvalue between0x30 and0x3FV + 3 digitsVCode versionnumberX Handshake YU Update firmware U = Success,Z = FailParallel mode - the pulse width input specificationIn pulse width mode, the input is a pulse width encoded signal with four direction linesand a common ground, similar to that used for telescope mount control. However, thepulse width per motor step is greatly reduced, so as to minimise the response time. Theminimum control pulse width is 10mS, which steps by 1 step in the appropriate direction.Longer pulses follow in a linear progression, increasing by 1 motor step for each 10mSincremental increase in pulse length. Note that only ONE input can be low at any onetime, otherwise other control functions may be inadvertently initiated.Various different functions can be triggered by ‘abnormal’ input pulse patterns. The mostuseful of these is the ‘centre’ mode, which should be used before beginning any guidingsequence. In this, the inputs are all taken low and then simultaneously released. The AOunit will then rapidly cycle between its limit switches and adjust the window to becentred in the dynamic range and normal to the incoming light. Other functions includethe transmission of commands through the AO system to the mount (for ‘bumping’ themount position) and various setup modes, mostly used for calibration during assembly.Please note that mount commands in serial mode can take place while further AOcommands are being received and acted upon. This allows the AO unit to follow themount correction and ‘back off’ the AO error without trailing the image. This is notavailable in parallel mode at the present time, but may be added later. Be careful not tosend multiple commands without allowing time for the previous one to complete.

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005The command list for parallel modePlease note that negative logic is used for all commands – an ‘active’ input is pulleddown to the ground (0v) rail. The directions of movement are based on an inverted imageand with the AO unit arranged with its North-South axis at 90 degrees to the Declinationaxis.Guiding functionsEast North South West Function0 0 0 0 Find Centre /Switch fromserial to parallelmode1 1 1 0 AO West1 1 0 1 AO South1 0 1 1 AO North0 1 1 1 AO East0 0 0 1 Mount West0 0 1 0 Mount South0 1 0 0 Mount North1 0 0 0 Mount East0 0 1 1 Force lowmotor speed1 1 0 0 Enter set upmodeSet up mode functions1 1 1 0 West motorforward1 1 0 1 South motorforward1 0 1 1 North motorforward0 1 1 1 East motorforward1 0 1 0 West motorback1 0 0 1 South motorback0 1 1 0 North motor

Handbook for the Starlight Xpress AO unitIssue 1 21/8/2005back0 1 0 1 East motorback0 0 1 1 All motorsdrive back0 0 0 0 All motorsdrive forward0 0 0 1 Enable serialmode and exitset up mode1 1 0 0 Exit set upmodeCopyright Starlight Xpress Ltd.September 2005

Handbook for the Starlight Xpress SXV AO unit

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