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The 4-meter Multi-Object Spectroscopic Telescope (4MOST), wide-field, high-multiplex spectroscopic survey facility will enable the simultaneous spectroscopy of up to 2400 targets within a 2.5° diameter field of view. A secondary guider system optical relay and data production description is described. The role of this guider is for fine rotational and target alignment corrections. The output of the 12 times 7 fibres are arranged such that the CCD detector can be read out in continuous read mode. The position of all fibres are illuminated at their spectrograph end and measured using a camera system at the positioner end. For the secondary guide bundles, only the central fibre is illuminated. A notch filter is used in the image relay in such a way that that the back illumination light is reflected from back illumination fibres to illuminate only the central fibres of each guide probe. This allows on-sky guiding while the fibres are being positioned.

Tony Hallas, then and now among the pantheon of great astroimagers, was explaining why the St-4 autoguider was the most important development of all time for amateur astroimagers.

This chapter focuses on some practical examples that illustrate alternative techniques. These are deliberately chosen to use a selection of different capture and processing programs and to cover a range of imaging problems and solutions. The autoguider system employs a Starlight Xpress Lodestar fitted to an off-axis guider, parfocal with the main imaging camera. The entire imaging chain is screw-coupled for rigidity; 2- or 1.25-inch eyepiece couplings are banished. The belt-drive systems in the high end mounts crucially have less DEC backlash too, ideal for autoguiding. Each system uses remote control; in the early days over a USB extender over Cat 5 module and later, using a miniature host PC, controlled over WiFi with Microsoft's Remote Desktop application. Most astronomical equipment is nominally rated at 12 volts but often accepts a range of 11.5–15 volts. Lead acid cells vary from about 13.8–11.0 volts over a full discharge, depending on load current and temperature.

Adaptive optics laser guide star systems perform atmospheric correction of stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order laser-correction. The requirement of a sufficiently bright guide star in the field-of-view to correct tip-tilt limits sky coverage. Here we show an improvement to effective seeing without the need for nearby bright stars, enabling full sky coverage by performing only laser-assisted wavefront correction. We used Robo-AO, the first robotic AO system, to comprehensively demonstrate this laser-only correction. We analyze observations from four years of efficient robotic operation covering 15,000 targets and 42,000 observations, each realizing different seeing conditions. Using an autoguider (or a post-processing software equivalent) and the laser to improve effective seeing independent of the brightness of a target, Robo-AO observations show a 39+/-19% improvement to effective FWHM, without any tip-tilt correction. We also demonstrate that 50% encircled-energy performance without tip-tilt correction remains comparable to diffraction-limited, standard Robo-AO performance. Faint-target science programs primarily limited by 50% encircled-energy (e.g. those employing integral field spectrographs placed behind the AO system) may see significant benefits to sky coverage from employing laser-only AO., Accepted for publication in The Astronomical Journal. 7 pages, 6 figures

The Echelle spectrograph operating at Vainu Bappu Telescope is a general purpose instrument designed for high-resolution spectroscopy. It is being considered for precision Doppler measurements without altering the existing design and basic usage. However, the design level limitations and environmental perturbations are a major source of instability and systematic errors. As a result, a small Doppler signal in the stellar spectra is completely swamped by the large and uncontrolled instrumental drift. We discuss some of the remedial measures we took to improve the radial velocity performance of the spectrograph. We show that an autoguider assembly has greatly reduced the mechanical jitter of the star image at the fiber input, making the illumination of the spectrograph slit at the other end stable. We have also installed an iodine absorption cell to track and eliminate the instrumental drifts to facilitate precision radial velocity observations. Furthermore, we have developed a generic algorithm that uses iodine exposures to extract the stellar radial velocities without the need for the complex forward modeling. Our algorithm is not accurate to the level of traditional iodine technique. However, it is convenient to use on a low-cost general-purpose spectrograph targeting a moderate radial velocity (RV) precision at a few 10 to 100 ms − 1 level. Finally, we have demonstrated the usefulness of our approach by measuring the RV signal of a well-known short-period, planet-hosting star.

The South African Astronomical Observatory (SAAO) is designing and manufacturing a wide-field camera for use on two of its telescopes. The initial concept was of a Prime focus camera for the 74” telescope, an equatorial design made by Grubb Parsons, where it would employ a 61mmx61mm detector to cover a 23 arcmin diameter field of view. However, while in the design phase, SAAO embarked on the process of acquiring a bespoke 1-metre robotic alt-az telescope with a 43 arcmin field of view, which needs a homegrown instrument suite. The Prime focus camera design was thus adapted for use on either telescope, increasing the detector size to 92mmx92mm. Since the camera will be mounted on the Nasmyth port of the new telescope, it was dubbed WiNCam (Wide-field Nasmyth Camera). This paper describes both WiNCam and the new telescope. Producing an instrument that can be swapped between two very different telescopes poses some unique challenges. At the Nasmyth port of the alt-az telescope there is ample circumferential space, while on the 74 inch the available envelope is constrained by the optical footprint of the secondary, if further obscuration is to be avoided. This forces the design into a cylindrical volume of 600mm diameter x 250mm height. The back focal distance is tightly constrained on the new telescope, shoehorning the shutter, filter unit, guider mechanism, a 10mm thick window and a tip/tilt mechanism for the detector into 100mm depth. The iris shutter and filter wheel planned for prime focus could no longer be accommodated. Instead, a compact shutter with a thickness of less than 20mm has been designed in-house, using a sliding curtain mechanism to cover an aperture of 125mmx125mm, while the filter wheel has been replaced with 2 peripheral filter cartridges (6 filters each) and a gripper to move a filter into the beam. We intend using through-vacuum wall PCB technology across the cryostat vacuum interface, instead of traditional hermetic connector-based wiring. This has advantages in terms of space saving and improved performance. Measures are being taken to minimise the risk of damage during an instrument change. The detector is cooled by a Stirling cooler, which can be disconnected from the cooler unit without risking damage. Each telescope has a dedicated cooler unit into which the coolant hoses of WiNCam will plug. To overcome an inherent drawback of Stirling coolers, an active vibration damper is incorporated. During an instrument change, the autoguider remains on the telescope, and the filter magazines, shutter and detector package are removed as a single unit. The new alt-az telescope, manufactured by APM-Telescopes, is a 1-metre f/8 Ritchey-Chretien with optics by LOMO. The field flattening optics were designed by Darragh O'Donoghue to have high UV throughput and uniform encircled energy over the 100mm diameter field. WiNCam will be mounted on one Nasmyth port, with the second port available for SHOC (Sutherland High-speed Optical Camera) and guest instrumentation. The telescope will be located in Sutherland, where an existing dome is being extensively renovated to accommodate it. Commissioning is planned for the second half of 2016.

The Carl Sagan Observatory is a new project for a remote observatory that will be built at the summit of Cerro Azul (a 2480 m mountain located near Magdalena. Sonora, México). It will include one 55 cm and four 14 cm telescopes. The 55 cm telescope will be dedicated to supernovae research. One of the 14 cm Maksutov telescopes will be used as an autoguider for the stellar observations. The other 14 cm telescopes will feature different narrow band filters that will be used for solar research. The observatory will be controlled from the campus of the Universidad de Sonora in Hermosillo, Sonora, México (~ 200 km from the site). A prototype of the observatory building has been built on campus and first light is expected by the end of May of 2001. We expect to have an operating mountain observatory by the end of 2002. Some of the unique technical aspects of this observatory, which we believe can be a model for future small telescope observatories are discussed in this work.

Measurement of stellar radial velocities (RV) is one acknowledged approach for planetary-search and asteroseismology programs. We study the incomplete scrambling action of a fiber feeding a spectrograph, which leaves RV errors at a level of few m/s. Observations realised with the ELODIE fiber-fed crossed-dispersion spectrograph at the 193-cm telescope of Observatoire de Haute-Provence (OHP) are presented. A fiber-locked autoguider (called FLAG) has been specifically built to reduce the stellar-beam geometrical fluctuations within the spectrograph. With FLAG, the fiber-input plays the role of guiding detector. Automatic focusing is also accomplished by the system. The design and performance characteristics of the instrument tested at the 152-cm telescope of OHP are reviewed here.

Spectronebulagraph, an automated observation system of tridimensional spectroscopy with a long slit spectrograph, is now in operation at the 188 cm telescope of the Okayama Astrophysical Observatory. This system is based on the local area net work of personal computers which control the telescope, the autoguider, the Cassegrain spectrograph and its CCD camera. Effects of variable atmospheric transmission during scans of target objects are removed by performing a set of two orthogonal scans and the data processing.A new spectrograph is now under development for the telescope. This instrument has multiple modes for tridimensional spectroscopy, i.e., the filter imagery mode, the imaging Fabry-Perot interferometer mode, a slit spectrograph mode for Spectronebulagraph, and the microlens array spectrograph (TIGER) mode. For the last mode, a dual preoptics to get simultaneously the sky background is introduced and achromatization of the microlenses is tried. This project is a part of development of a prototype instrument for the SUBARU telescope.

Once you have your ‘scope in focus, your target image framed properly, and your dark frames taken with your imaging program set to automatically subtract the dark frames for you, you are ready to start your imaging session. The next decision you will have to make is how long of an exposure to use for your images.

The "Photon Collider" uses a compact array of four off axis autoguider cameras positioned with independent filtering and focus. The photon collider is two way symmetric and robustly mounted with the off axis light crossing the science field which allows the compact single frame construction to have extremely small relative deflections between guide and science CCDs. The photon collider provides four independent guiding signals with a total of 15 square arc minutes of sky coverage. These signals allow for simultaneous altitude, azimuth, field rotation and focus guiding. Guide cameras read out without exposure overhead increasing the tracking cadence. The independent focus allows the photon collider to maintain in focus guide stars when the main science camera is taking defocused exposures as well as track for telescope focus changes. Independent filters allow auto guiding in the science camera wavelength bandpass. The four cameras are controlled with a custom web services interface from a single Linux based industrial PC, and the autoguider mechanism and telemetry is built around a uCLinux based Analog Devices BlackFin embedded microprocessor. Off axis light is corrected with a custom meniscus correcting lens. Guide CCDs are cooled with ethylene glycol with an advanced leak detection system. The photon collider was built for use on Las Cumbres Observatory's 2 meter Faulks telescopes and currently used to guide the alt-az mount.

Maximum sensitivity for optical interferometers is achieved only when the optical pathlengths between the different arms can be equalized without using interference fringes on the research object itself. This is called “blind operation” of the interferometer. In this paper I examine different options to achieve this, focussing on the application to the Very Large Telescope Interferometer (VLTI). It is proposed that blind operation should be done using a so-called “coherence autoguider”, working on an unresolved star of magnitude V=11 to 13 within the “isoplanatic patch for coherencing”, which has a diameter of about 1 degree. Estimates of limiting magnitudes for the VLTI are also derived.

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The UKIRT Wide-Field Camera (WFCAM) was commissioned in two phases between October and December 2004, and March and April 2005. It has been carrying out full-scale sky survey operations since May 2005. This paper describes the commissioning process and compares actual performance on the telescope with specifications in four key areas: optical image quality including delivered FWHM and ghosting etc., noise and sensitivity in the infrared and on the visible autoguider, array artifacts such as crosstalk and persistent images, and observing efficiency. A comprehensive program of science verification was carried out before commencing the UKIRT Infrared Deep Sky Survey (UKIDSS).

In late 2003 the Isaac Newton Group of Telescopes (ING) successfully completed the commissioning of a set of new CCD Autoguider and Television cameras on the 4.2m William Herschel Telescope (WHT). These new multi-purpose heads are built around E2V CCD4720 and CCD5710 frame-transfer detectors fitted with integral Peltier coolers. These new cameras use the same type of CCD controller and Data Acquisition System (DAS) as all of ING’s CCD science cameras and Infrared arrays. These multi-purpose heads have replaced a diverse set of older and difficult-to-maintain Television and Autoguiding systems. The approach of using the same DAS + controller for all cameras at ING greatly aids their maintainability. This paper looks at the reasons for developing the cameras, takes a detailed look at the design and examines existing and possible future applications.

When affordable CCD cameras first appeared on the scene in the late 1980s and early 1990s, amateur planetary observers were keen to appreciate their potential for shortening exposure times and “freezing” the atmospheric turbulence that is the bane of the astrophotographer. Indeed the SBIG ST4, the amateur astronomer’s first commercial CCD camera, soon stopped being seen as an autoguider because it was more exciting as a planet imager! CCD cameras also have other advantages over film cameras as well as just raw sensitivity. They don’t suffer from harmful shutter and reflex mirror vibration (although some do have moving vanes for facilitating dark frames); images can be viewed immediately; thousands of images per night can be taken; and, most important, images can be stacked and processed to bring out the maximum detail.

An update on the design status of the UKIRT Wide Field Camera (WFCAM) is presented. WFCAM is a wide field infrared camera for the UK Infrared Telescope, designed to produce large scale infrared surveys. The complete system consists of a new IR camera with integral autoguider and a new tip/tilt secondary mirror unit. WFCAM is being designed and built by a team at the UK Astronomy Technology Centre in Edinburgh, supported by the Joint Astronomy Centre in Hawaii. The camera uses a novel quasi-Schmidt camera type design, with the camera mounted above the UKIRT primary mirror. The optical system operates over 0.7 - 2.4 μm and has a large corrected field of view of 0.9° diameter. The focal plane is sparsely populated with 4 2K x 2K Rockwell HAWAII-2 MCT array detectors, giving a pixel scale of 0.4 arcsec/pixel. A separate autoguider CCD is integrated into the focal plane unit. Parallel detector controllers are used, one for each of the four IR arrays and a fifth for the autoguider CCD.

The servo design and model of the W. M. Keck telescopes autoguider is presented. Telescope servo models often do not include the guider loop and therefore do not take advantage of traditional control analysis and test techniques to improve performance. Guide camera dynamics, computational and transport lags, and compensation networks are discussed. A means of measuring the actual frequency response characteristics of the guide loop is presented and the results are compared to those predicted by the model. Guide performance as a function of integration time is illustrated. An improved compensation network is developed and its performance examined.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Gemini telescope control system (TCS) uses an integrated pointing/tracking scheme, based on the 'virtual telescope' (VT) concept, but extended to encompass autoguiding and control of the chopping secondary (M2). The TCS treats each autoguider probe as a separate VT, with a different target from the main telescope (namely a guidestar instead of a science source), different color, flexure and so on. The constraint that both the guider VT and the main-telescope VT share one mount (Az,El) enables the (x,y) of the guidestar image to be predicted. Comparisons between the predicted and measured (x,y) positions enable the guiding system to generate rapid adjustments to M2 tip/tilt, taking out windshake as well as other tracking errors. The TCS monitors M2 tip/tilt and adjusts the mount pointing as required, preventing unwanted buildup of M2 offset. Independent control of M2, to accomplish rapid scans while smoothly tracking the (Az,El) mount for example, is provided by having separate 'mount' and 'source' VTs. In this case, the constraint that there is only one mount (Az, El) enables the M2 tip/tilt to be determined which will place the target image in the required place. Chopping is done by implementing the different chop states as different VTs all running in parallel. The TCS is oblivious to the use being made of the different M2 tip/tilts that the different chop states call for, that being left to the various subsystems. The Gemini plan calls for five VTs (two permanent guide detectors and one on-instrument, plus the mount and target VTs), and all but the mount VT support three chop states. Operating at rate of 20 Hz, this means that the entire pointing calculation has to be performed 260 times per second, and some care has been taken to organize the computations efficiently.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We first became acquainted, through a local astronomical society, in 1991. Both of us had recently and independently made first steps into CCD imaging with the purchase of an SBIG ST4 autoguider and Electrim EDC1000TE CCD camera. Deciding to pool resources from then on, we purchased an SBIG ST6 and concentrated on producing some of the UK’s first tri-colour CCD images.

We describe a series of five CCD cameras designed by Gordian for low light-level applications. The first device is a low-cost non-imaging astronomical autoguiding tracker based on the Texas Instruments TC255 CCD chip and an MC6811 microcontroller. Mounting off-axis, it provides standardized tracking-motor signals for any telescope with a dual-axis drive corrector, automatically compensating for the mechanical peculiarities of the drive, set- up factors, and pointing errors. The tracker can guide to +/- 1 arcsec on an 8th magnitude star when used with an 8' aperture, f/10 telescope. The basic autoguider design has been extended to produce self-contained 8-bit and 16-bit imaging cameras with autoguiding functionality. Images are buffered in PSRAM, then relayed to a host PC via an RS-232 serial connection. The addition of regulated thermoelectric cooling reduces CCD thermal noise and alleviates dark current saturation. Gordian has also designed two high-resolution cameras based on the Kodak KAF-0400 and KAF-1600 CCDs. The cameras produce 16-bit images with 768 X 512 pixels or 1536 X 1024 pixels, respectively. Pixel size is 9 micrometers square. The camera head contains the CCD, thermoelectric cooling mechanism, analog electronics, and a custom-designed electromechanical shutter based on FlexinolTM actuator wire. A separate base unit houses a Motorola 68306 microprocessor and associated electronics for telescope control and on-board image processing. A stepper-motor based filter wheel can be attached directly to the camera head. The camera communicates with a personal computer via SCSI or serial connection. Software for the host PC provides additional control options, data storage, and image processing capability.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The INT Prime Focus Mosaic Camera (INT PFC) is designed to provide a large field survey and supernovae search capability for the prime focus of the 2.5 m Isaac Newton Telescope (INT). It is a joint collaboration between the Royal Greenwich Observatory (UK), Kapteyn Sterrenwacht Werkgroep (Netherlands), and the Lawrence Berkeley Laboratories (USA). The INT PFC consists of a 4 chip mosaic utilizing thinned and anti-reflection coated CCDs. These are LORAL devices of the LICK3 design. They will be operated cryogenically in a purpose built camera assembly. A fifth CCD, of the same type, is co-mounted with the science array in the cryostat to provide autoguider functions. This cryostat then mounts to the main camera assembly at the prime focus. This assembly will include standard filters and a novel shutter wheel which has been specifically designed for this application. The camera will have an unvignetted field of 40 arcminutes and a focal ratio of f/3.3. This results in a very tight mechanical specification for co-planarity and flatness of the array of CCDs and also quite stringent flexure tolerance of the camera assembly. A method of characterizing the co- planarity and flatness of the array will be described. The overall system architecture will also be described. One of the main requirements is to read the whole array out within 100s, with less than 10e rms. noise and very low CCD cross talk.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper we describe the hardware and software architecture of the Automatic Imaging Telescope (AIT), recently developed at the Perugia University Observatory. It is based on an existing 0.4 m telescope which was transformed into an automatic device. During the night, all the observatory functions are controlled by two PCs in an unattended mode. The system is equipped with an autoguider and the software was designed to allow the automatic reduction of the data at the end of the night. Since October 1994 the AIT has been collecting a large amount of BVRcIc data for about 30 blazars.

Recently, a number of technical improvements in the Infrared Spatial Interferometer (ISI) helped to increase the signal-to- noise ratio in fringe power by about a factor of two over the previously reported factor of 10. The improvements comprise higher quantum efficiency and larger bandwidth HgCdTe heterodyne detectors, better IF signal processing components, new lock-in amplifiers, a fringe calibration system and an enhanced autoguider. A comprehensive effort to characterize and improve the short-term and long-term stability of the infrared detection system led to a large improvement of the calibration of visibility data. The ISI has been used on baselines of 10- and 32-m length during the last observing season. Fringes were obtained on 8 sources on the 32-m baseline so far. This paper described recent system upgrades and a new filter bank for spectroscopy on molecular lines, as well as some more studies of atmospheric fluctuations. Results of our astrophysics and astrometry programs are reported in the following three papers.

The Anglo-Australian Telescope's horseshoe equatorial mount is driven from its northern end by a 3.6-meter diameter straight-spur gearwheel. The telescope's tracking performance depends critically on the accuracy of this gearwheel and on the gearbox which couples it to the hour-angle encoder system. Early tests on the telescope showed that the gear systems were very accurate, though some small errors were detected. Analysis of autoguider records obtained during the period 1990-93 have recently been used to calibrate these errors, and software to apply appropriate corrections have been added to the AAT control system. In tests of the new software, a 15-minute unguided CCD exposure showed circular 0.9 arcsec FWHM star images; a similar exposure with the corrections disabled had trailed images where the east-west FWHM had worsened to 1.5 arcsec.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The altitude and azimuth axes of the VLT telescopes will be controlled by special designed servo controllers. These controllers are designed to minimize the effect of disturbances. The properties of all elements of these servo systems: mechanical system, motors, amplifiers, tachometer, encoder and finally the servo controller itself will be presented. Aspects like sensor noise, hysteresis, friction and bandwidth limits are described and the effect of each of them on the servo performance is evaluated. A systematic analysis of the effect of external disturbances to the servo system, mainly the wind, is included. The frequency spectrum of the wind that can be expected in the VLT enclosure is compared with disturbance sensitivity of the servo system. This analysis provides the power spectral density of the axial rotation. The reduction of this rotation with an autoguider and/or field stabilization (a fast servo system, which includes a tip/tilt of the secondary mirror) can then be judged. The data for the analysis has been derived from the present status of the VLT main structure design. The servo elements as described above are now in a well-defined state.

The azimuth and elevation sources of the W.M. Keck Telescope have been designed to meet stringent tracking, offsetting, and slewing requirements. The requirements and the achieved performance are presented. The feedback architecture of the position and rate loops is described. The analysis includes an identification of the telescope structure via frequency sweep test signals. The identified model is compared with the single resonance model used in the preliminary design. As expected there are numerous additional resonances, and the effects of these on performance and stability are discussed. The autoguider loop is also discussed. Shortcomings are noted and ideas for improved performance are examined.

The requirements of a charge coupled device (CCD) autoguider camera and the specifications of a camera that we propose to build to meet those requirements will be discussed. The design goals of both the package and the electronics will be considered.

A telescope autoguider constructed of unmodified commercially available components for use with the 2.1-m focal reducer at McDonald Observatory is described. The system comprises a thermoelectrically cooled CCD camera with format 384 x 576 pixels, pixel size 23 microns square, readout noise 25 electrons/pixel, and dark current 10 electrons/sec pixel at -35 C; a 50-mm camera lens giving resolution about 1 arcsec/pixel; an IEEE-488 data bus; a MicroVAX 3200 computer workstation; and a serial-to-parallel converter permitting the computer to address the telescope drive system via four trail-rate controls. Also discussed are the top-down C-language programming approach, the data representation, the autoguiding and search algorithms, and ongoing work on the telescope control algorithm. It is suggested that the present system is versatile enough to be applicable to many similar telescopes.

The CCD autoguider detector system for the William Herschel Telescope (WHT) comprises a Peltier cooled, slow-scan CCD camera supported by an MC68020-based VME computer for image processing. The detector is a fluorescent dye coated EEV P8603 CCD chip operated in frame transfer mode. The CCD controller enables a full image to be read out during acquisition, but with windowed readout during guiding so as to permit an increased frame rate. The windowing is controlled by the VME computer, which is also used to calculate the centroid of the guide star and provides a local user interface, displaying images and guider status information. Special attention has been paid to the CCD drive clocks and bias voltages, enabling a very low dark current to be achieved (2 electrons per pixel per second at -35 C) without the need for extreme cooling. Guiding to magnitude 19 on the WHT has been demonstrated during dark time, with an integration time of one second.

Spectro-nebula graph (SNG), a tridimensional-spectroscopic system, has been developed as a versatile observation system attached to the Cassegrain focus of the 1.88 m telescope at the Okayama Astrophysical Observatory. Tridimensional spectra, i.e., so-called data cubes, are obtained by sweeping the telescope in the direction perpendicular to the slit of a spectrograph step by step. From the data cube, various monochromatic images can be extracted by data processing. SNG consists of four devices, i.e., the telescope control system, the autoguider, the spectrograph, and the CCD camera, which are distributed on a personal computer network. The control software for SNG performs cooperative control of four devices in an automated fashion according to a programmed sequence of procedures. Some observational results taken with SNG are shown for 3C 120, NGC 4449, and NGC 3646.

A proportional control astronomical autoguider has been built using the low-noise photon-counting system described by Fegan and Craven (1977). The guider has a dynamic range of ten stellar magnitudes and has output options for driving either conventional or stepping motors. Proportional control is obtained in both cases.

Publisher Summary This chapter provides an overview of an 8 cm electronographic image tube. The previous electronographic tube with a 4 cm diameter mica window displayed a number of problems, and it took longer than expected to produce tubes with satisfactory characteristics. The most time consuming of these problems were: (a) loss of photocathode sensitivity due to poisoning by residual gases, and (b) securing good contact between the nuclear emulsion and the mica window. Dark current had also been a problem in some tubes. The 4 cm tube has been used astronomically with the 36 inch telescope at Herstmonceux, and in Israel with the 40 inch at the Wise Observatory, Mitzpeh Ramon. The 8 cm tube includes a quadrant silicon diode for the use as an autoguider sensor. It is intended that an 8 cm tubes with autoguider should be mounted at the prime focus of the 98 inch Isaac Newton telescope. The tube will have a remotely controlled film changing mechanism with cassettes allowing five exposures. Acquisition of a guide star will also be remotely controlled using a TV camera on the finder telescope.

The operation and performance of a Digicon-based autoguider system recently developed will be discussed. The photosensor is a twelve-channel, photon-counting Digicon specifically developed by SAI for this application. The design and implementation of the system will be discussed with an emphasis on the objective of developing a general purpose auto-guider system for a wide range of applications. Data will be presented on the Digicon performance, i.e., quantum efficiency, background count rate, and pulse counting performance. In addition, overall system guiding accuracy, dynamic range, and sensitivity will be detailed.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The autoguiding of ground-based telescopes has developed relatively slowly over the last thirty years or so, in spite of the existence of exceedingly sensitive photoelectric detectors. Of those based on the mechanical chopping or dissection of the light in a stellar image, there are essentially three types. The first (Ref. 1) entails division of the light at the roof of a right-angled prism or the apex of a pyramid, the second, a rotating knife-edge (Ref. 2), and the third, an elegant development of the latter (Ref. 3), uses a ball bearing rotating inside an annulus.© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

To eliminate image motion and blur (caused by "seeing" effects of the Earth's atmosphere) it is necessary to introduce an optical system which produces a real image of the pupil (the primary mirror) followed by a reimaged portion of the field. For the Canada-France-Hawaii telescope (CFHT) at the prime focus, these optics are required to magnify the field from F/3.8 (which is the primary focal ratio of the telescope) to F/17 so that the electronic detector can adequately sample stellar images of 0.25 arcsec diameter. The image motion is removed at the pupil. A simple but wasteful method is to locate a shutter at the pupil which opens only when a guide star is in the mid position of its motion. The guide starlight is taken from the centre of the field before the light reaches the pupil and feeds an autoguider. An alternative is to locate a flat mirror at the pupil which is rapidly deflected to remove the seeing motion. Tests conducted by staff of the CFHT Corporation produced photographs showing 0.25 arcsec resolution using the prime focus corrector followed by an off-the-shelf lens. However this lens produced poor images off the centre of the 4 arcmin field within which the image motions might follow those of the guide star. Custom designed optical systems are described which produce sharp images over a wide spectral region and also provide the option of doing without the prime focus corrector resulting in higher transmission, less stray light and better resolution than in the trial arrangement.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A crucial feature of large telescopes using multiple objectives is the ability to align the optics so that the different star images coincide to within a fraction of the image size. Initially this was intended to be done in the MMT with the "laser active optics" system in which the six telescopes were coaligned by means of artificial laser-star images generated by a seventh guide-alignment telescope. That system was found to be less than satisfactory mostly because of internal seeing and scattered light effects. Instead we have constructed the Telescope Coalignment System (or TCS) in which the telescopes are co-aligned on stellar images. The TCS is an autoguider which works simultaneously on six telescopes and which therefore automatically coaligns the telescopes and tracks them on a field star. When a field star is not present in the small 4 arc minute field of view of the MMT the TCS system coaligns the MMT on a nearby star and then tracks and maintains co-alignment of the six telescopes under computer control using separate flexure corrections for each one.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A microprocessor-based telescope autoguider is described that uses the signal from an existing field acquisition TV camera to generate tracking-error information for an optical telescope. The guider can accept input from any black and white video camera conforming to NTSC (EIA RS-170) standards. This autoguider has been used for several years on the Shane 3-meter telescope at Lick Observatory.

The automatic offset guider at the prime focus of the AAT is described. A description of the guider and its organization in the telescope's computerized drive system is followed by the initial results obtained with it. Key words: autoguider - main-beam guidance - telescope instrumentation - computerized guidance

We present here some of the techniques used to automate many of the observing tasks on the 0.91-meter telescope of the Goethe Link Observatory. A description of the method used to calculate the dome position for a telescope which is mounted asymmetrically is included. We also give details of a novel autoguider. This autoguider uses a digitized television image of the star field to enable the microcomputer to generate error signals from a centroid calculation.