Many areas of astronomical research rely on deep blue wide-field imaging. Mauna Kea enjoys the very best UV transparency from the ground and the Keck telescopes with 10 meter f/1.75 primaries are well suited to a prime focus camera with a large angular field. Swinburne University leads a proposal to provide a camera (KWFI, for Keck Wide Field Imager) that is optimized in the UV but works well to 1μm wavelength. Keck has interchangeable top end modules, of which one is now unused and easily capable of housing the required corrector lens and detector enclosure. This paper concentrates on details of the KWFI optical design.
A few telescope projects plan to feed spectrographs through thousands of fibres, needing metrology accuracy for feedback of just a few μm. This generally requires accuracy at the metrology camera better than 0.1 arcsec, which can be frustrated by local seeing. With fiducials situated with the array of science fibres, seeing displacements can be calibrated, with accuracy depending on the fiducial spacing. Fiducials within the field usually require sacrificing science fibres but AAO’s positioner for MSE will take advantage of its tilting spines and a special but simple metrology camera to provide a multitude of fiducials within the field with no such sacrifice.
MANIFEST is a multi-object fibre facility for the Giant Magellan Telescope that uses ‘Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeinglimited instruments, offers access to larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via integral-field-units; image-slicers; and in some cases higher spatial and spectral resolution. The TAIPAN instrument on the UK Schmidt Telescope is now close to science verification which will demonstrate the feasibility of the Starbug concept. We are now moving into the conceptual development phase for MANIFEST, with a focus on developing interfaces for the telescope and for the instruments.
Maunakea Spectroscopic Explorer will be a 10-m class highly multiplexed survey telescope, including a segmented primary mirror and robotic fiber positioners at the prime focus. MSE will replace the Canada France Hawaii Telescope (CFHT) on the summit of Mauna Kea, Hawaii. The multiplexing includes an array of over four thousand fibers feeding banks of spectrographs several tens of meters away.
We present an overview of the requirements flow-down for MSE, from Science Requirements Document to Observatory Requirements Document. We have developed the system performance budgets, along with updating the budget architecture of our evolving project. We have also identified the links between subsystems and system budgets (and subsequently science requirements) and included system budget that are unique to MSE as a fiber-fed facility.
All of this has led to a set of Observatory Requirements that is fully consistent with the Science Requirements.
In this paper we present recent progress on the Australian Astronomical Observatory’s AESOP2 fiber positioner for 4MOST (on VISTA). As an evolution of the Echidna “spine” technology used for FMOS (on Subaru), AESOP has challenging requirements to position 2,448 fibers in parallel, within 1 minute, to an accuracy of < 10 um RMS. AESOP successfully passed ESO’s official final design review and manufacturing has commenced. We present performance results from the first batch of newly-manufactured positioners and also report on how the AESOP project is tracking in terms of schedule, budget and risk.
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The metrology system determines the position of the back-illuminated fibres on the focal surface of the telescope. It consists of 4 identical cameras that are mounted on the spider vanes of the secondary mirror of the VISTA telescope and look through the entire optical train, including M1, M2 and the WFC/ADC unit. Here, we present an exhaustive study on the expected centroiding errors, including but not limited to lens fabrication errors, seeing, mirror distortions and parallax effects.
The Australian Astronomical Observatory’s (AAO’s) AESOP project is part of the 4 metre Multi-Object Spectrograph Telescope (4MOST) system for the VISTA telescope. It includes the 2436-fiber positioner, space frame and electronics enclosures. The AESOP concept and the role of the AAO in the 4MOST project have been described in previous SPIE proceedings. Prototype tests, which were completed early in 2017 demonstrated that the instrument requirements are satisfied by the design. The project final design stage has recently been completed. In this paper, key features of the AESOP positioning system design, along with the techniques developed to overcome key mechanical, electronic, and software engineering challenges are described. The major performance requirement for AESOP is that all 2436 science fiber cores and 12 guide fiber bundles are to be re-positioned to an accuracy of 10 µm within 1 minute. With a fast prime-focus focal-ratio, a close tolerance on the axial position of the fiber tips must be held so efficiency does not suffer from de-focus losses. Positioning accuracy is controlled with the metrology cameras installed on the telescope, which measures the positions of the fiber tips to an accuracy of a few µm and allows iterative positioning until all fiber tips are within tolerance. Maintaining co-planarity of the fiber tips requires accurate control in the assembly of several components that contribute to such errors. Assembly jigs have been developed and proven adequate for this purpose. Attaining high reliability in an assembly with many small components of disparate materials bonded together, including piezo ceramics, carbon fiber reinforced plastic, hardened steel, and electrical circuit boards, has entailed careful selection and application of cements and tightly controlled soldering for electrical connections.
Based on the success of the SAMI integral field spectrograph (IFS) instrument on the Anglo-Australian Telescope (AAT) the capacity for large IFS nearby galaxy surveys on the AAT is being substantially expanded with a new instrument called Hector. The high filling-fraction imaging fibre bundles ‘hexabundles’ of the type used on SAMI, are being enlarged to cover up to 30-arcsec diameter. The aim is to reach two effective radii on most galaxies, where the galaxy rotation curve flattens and >75% of the specific angular momentum of disk galaxies is accounted for. Driven by the key science case, Hector will have a 1.3A spectral resolution, enabling high-order stellar kinematics to be measured on a larger fraction of galaxies than with any other IFS instrument. Hector will be on sky in 2019.
The first module of Hector, Hector-I, will have 21 hexabundles and >42 sky fibres to observe 20 galaxies and a calibration star simultaneously. It consists of new blue and red-arm spectrographs that have been designed at the Australian Astronomical Observatory (AAO; now called AAO-Macquarie), coupled to the new hexabundles and robotic positioner from AAO-USydney (formerly the Sydney Astrophotonics Instrumentation Laboratory, SAIL) at Sydney University. A novel robotic positioning concept will compensate for varying telecentricity over the 2-degree-field of the AAT to recoup the 20% loss in light at the edge of the field. Hector-I will survey 15,000 galaxies. Additional modules in the future would result in 30,000 galaxies.
Hector will take integral field spectroscopy on galaxies with z<0.15 in the 4MOST WAVES-North and WAVES-South∗ regions. The WAVES data, which will come later, will give the environment metrics neces- sary to relate how local and global environments influence galaxy growth through gas accretion, star formation and spins measured with Hector. The WALLABY ASKAP† survey will trace HI gas across the Hector fields, which in combination with Hector will give a complete view of gas accretion and star formation.
In this paper we present the Australian Astronomical Observatory’s concept design for Sphinx - a fiber positioner with 4,332 “spines” on a 7.77mm pitch for CFHT’s Mauna Kea Spectroscopic Explorer (MSE) Telescope. Based on the Echidna technology used with FMOS (on Subaru) and 4MOST (on VISTA), the next evolution of the tilting spine design delivers improved performance and superior allocation efficiency. Several prototypes have been constructed that demonstrate the suitability of the new design for MSE. Results of prototype testing are presented, along with an analysis of the impact of tilting spines on the overall survey efficiency. The Sphinx fiber positioner utilizes a novel metrology system for spine position feedback. The metrology design and the careful considerations required to achieve reliable, high accuracy measurements of all fibers in a realistic telescope environment are also presented.
AST3-NIR is a new infrared camera for deployment with the AST3-3 wide-field survey telescope to Dome A on the Antarctic plateau. This project is designed to take advantage of the low Antarctic infrared sky thermal background (particularly within the Kdark near infrared atmospheric window at 2.4 μm) and the long Antarctic nights to provide high sensitivity temporal data from astronomical sources. The data collected from the Kunlun Infrared Sky Survey (KISS) will be used to conduct a range of astronomical science cases including the study of supernovae, exo-planets, variable stars, and the cosmic infrared background.
ULTIMATE is an instrument concept under development at the AAO, for the Subaru Telescope, which will have the unique combination of ground layer adaptive optics feeding multiple deployable integral field units. This will allow ULTIMATE to probe unexplored parameter space, enabling science cases such as the evolution of galaxies at z ~ 0:5 to 1.5, and the dark matter content of the inner part of our Galaxy. ULTIMATE will use Starbugs to position between 7 and 13 IFUs over a 14 × 8 arcmin field-of-view, pro- vided by a new wide-field corrector. All Starbugs can be positioned simultaneously, to an accuracy of better than 5 milli-arcsec within the typical slew-time of the telescope, allowing for very efficient re-configuration between observations. The IFUs will feed either the near-infrared nuMOIRCS or the visible/ near-infrared PFS spectrographs, or both. Future possible upgrades include the possibility of purpose built spectrographs and incorporating OH suppression using fibre Bragg gratings. We describe the science case and resulting design requirements, the baseline instrument concept, and the expected performance of the instrument.
We present an alternative Corrector-ADC design for GMT. The design consists of just 3 silica lenses, of maximum size 1.51m, and includes only a single low-precision asphere for 20' field-of-view, and none for 10'. The polychromatic (360nm-1300nm) image quality is d80<0.043" at zenith and d80<0.20" for ZD<60 degrees. The monochromatic image quality is d80<0.1" everywhere, and typically ~0.05". The ADC action is achieved by tilt and translation of all three lenses; L1 and L2 via simple slide mechanisms each using a single encoded actuator, and L3 via a novel ‘tracker-ball’ support and three actuators. There is also a small motion of M2 via the hexapod, automatically generated by the AGWS system. The ADC action causes a small non-telecentricity, but this is much less than the unavoidable chromatic effects shared with the baseline design. The ADC action also changes the distortion pattern of the telescope, but this can be used positively, to reduce the maximum image motion due to differential refraction by a factor of three. The transmission is superb at all wavelengths, because of the reduced number of air/glass surfaces, and the use only of fused silica.
Optical designs are presented for the Maunakea Spectroscopic Explorer (MSE) telescope. The adopted baseline design is a prime focus telescope with a segmented primary of 11.25m aperture, with speed f/1.93 and 1.52° field-of-view, optimized for wavelengths 360-1800nm. The Wide-Field Corrector (WFC) has five aspheric lenses, mostly of fused silica, with largest element 1.33m diameter and total glass mass 788kg. The Atmospheric Dispersion Corrector (ADC) is of the compensating lateral type, combining a motion of the entire WFC via the hexapod, with a restoring motion for a single lens. There is a modest amount of vignetting (average 5% over the hexagonal field); this greatly improves image quality, and allows the design to be effectively pupil-centric. The polychromatic image quality is d80<0.225"/0.445" at ZD 0/60° over more than 95% of the hexagonal field-of-view. The ADC action allows adjustment of the plate-scale with zenith distance, which is used to halve the image motions caused by differential refraction. A simple design is presented for achieving the required ADC lens shifts and tilts. A two-mirror design was also undertaken for MSE, but was not selected. This is a 12.3m F/2.69 forward Cassegrain design, with a 2.75m diameter M2, and three silica lenses, of largest diameter 1.33m. The field-of-view is again 1.52°. The f/0.95 primary makes the design remarkably compact, being under 10m long. The ADC action involves a small motion of M2 (again via a hexapod), and shifts and tilts of a single lens. The design is effectively pupil-centric, with modest vignetting (5.9% average). The image quality is virtually identical to the prime focus design.
Hector[1,2,3] will be the new massively-multiplexed integral field spectroscopy (IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the next main dark-time instrument for the observatory. Based on the success of the SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is being improved to a new innovative design for Hector. The distribution of hexabundle angular sizes is matched to the galaxy survey properties in order to image 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging bundles will be positioned by ‘starbug’ robots across a new 3-degree field corrector top end to be purpose-built for the AAT. Many thousand fibres will then be fed into new replicable spectrographs. Fundamentally new science will be achieved compared to existing instruments due to Hector's wider field of view (3 degrees), high positioning efficiency using starbugs, higher spectroscopic resolution (R=3000-5500 from 3727-7761Å, with a possible redder extension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre cores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion and merger history and large-scale environment made every galaxy different in its morphology and star formation history. The high resolution, particularly in the blue, will make Hector the only instrument to be able to measure higher-order kinematics for galaxies down to much lower velocity dispersion than in current large IFS galaxy surveys, opening up a wealth of new nearby galaxy science.
The Maunakea Spectroscopic Explorer is designed to be the largest non-ELT optical/NIR astronomical telescope, and will be a fully dedicated facility for multi-object spectroscopy over a broad range of spectral resolutions. The MSE design has progressed from feasibility concept into its current baseline design where the system configuration of main systems such as telescope, enclosure, summit facilities and instrument are fully defined. This paper will describe the engineering development of the main systems, and discuss the trade studies to determine the optimal telescope and multiplexing designs and how their findings are incorporated in the current baseline design.
We present Simulated Annealing fiber-to-target allocation simulations for the proposed DESI and 4MOST massively multiplexed spectroscopic surveys. We simulate various survey strategies, for both Poisson and realistically clustered mock target samples. We simulate both Echidna and theta-phi actuator designs, including the restrictions caused by the physical actuator characteristics during repositioning. For DESI, with theta-phi actuators, used in 5 passes over the sky for a mock ELG/LRG/QSO sample, with matched fiber and target densities, a total target allocation yield of 89.3% was achieved, but only 83.7% for the high-priority Ly-alpha QSOs. If Echidna actuators are used with the same pitch and number of passes, the yield increases to 94.4% and 97.2% respectively, representing fractional gains of 5.7% and 16% respectively. Echidna also allows a factor-of-two increase in the number of close Ly-alpha QSO pairs that can be observed. Echidna spine tilt causes a variable loss of throughput, with average loss being the same as the loss at the rms tilt. The simulated annealing allows spine tilt minimization to be included in the optimization, at some small cost to the yield. With a natural minimization scheme, we find an rms tilt always close to 0.58 x maximum. There is an additional but much smaller defocus loss, equivalent to an average defocus of 30 μm. These tilt losses offset the gains in yield for Echidna, but because the survey strategy is driven by the higher priority targets, a clear survey speed advantage remains. For 4MOST, high and low latitude sample mock catalogs were supplied by the 4MOST team, and allocations were carried out with the proposed Echidna-based positioner geometry. At high latitudes, the resulting target completeness was 85.3% for LR targets and 78.9% for HR targets. At low latitude, the target completeness was 93.9% for LR targets and 71.2% for HR targets.
We present advances in the patented Echidna 'tilting spine' fiber positioner technology that has been in operation since 2007 on the SUBARU telescope in the FMOS system. The new Echidna technology is proposed to be implemented on two large fiber surveys: the Dark Energy Spectroscopic Instrument (DESI) (5000 fibers) as well the Australian ESO Positioner (AESOP) for 4MOST, a spectroscopic survey instrument for the VISTA telescope (~2500 fibers). The new 'superspine' actuators are stiffer, longer and more accurate than their predecessors. They have been prototyped at AAO, demonstrating reconfiguration times of ~15s for errors of <5 microns RMS. Laboratory testing of the prortotype shows accurate operation at temperatures of -10 to +30C, with an average heat output of 200 microwatts per actuator during reconfiguration. Throughput comparisons to other positioner types are presented, and we find that losses due to tilt will in general be outweighed by increased allocation yield and reduced fiber stress FRD. The losses from spine tilt are compensated by the gain in allocation yield coming from the greater patrol area, and quantified elsewhere in these proceedings. For typical tilts, f-ratios and collimator overspeeds, Echidna offers a clear efficiency gain versus current r-that or theta-phi positioners.
Hector is an instrument concept for a multi integral-field-unit spectrograph aimed at obtaining a tenfold increase in
capability over the current generation of such instruments. The key science questions for this instrument include how do
galaxies get their gas, how is star formation and nuclear activity affected by environment, what is the role of feedback,
and what processes can be linked to galaxy groups and clusters. The baseline design for Hector incorporates multiple
hexabundle fibre integral-field-units that are each positioned using Starbug robots across a three-degree field at the
Anglo-Australian Telescope. The Hector fibres feed dedicated fixed-format spectrographs, for which the parameter space
is currently being explored.
4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large
area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with ~2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; ~1600 fibres go to two spectrographs with resolution R<5000 (λ~390-930 nm) and
~800 fibres to a spectrograph with R>18,000 (λ~392-437 nm and 515-572 nm and 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the
southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing
concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020.
This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more
detailed descriptions of the instrument concept, the instrument requirements development, the systems engineering implementation, the instrument model, the fibre positioner concepts, the fibre feed, and the spectrographs.
A 2.5 degree field diameter corrector lens design for the Cassegrain focus of the VISTA 4 meter telescope is presented.
It comprises four single elements of glasses with high UV transmission, all axi-symmetric for operation at the zenith.
One element is displaced laterally to provide atmospheric dispersion correction. A key feature, especially beneficial for
the VISTA application, is that the ADC element can be mounted so it is driven simply by gravity; thus its operation
needs no motors, encoders, cabling, or software control. A simple mechanical design to achieve this and the optical
performance details are described.
Wide-Field Corrector designs are presented for the Blanco and Mayall telescopes, the CFHT and the AAT. The designs
are Terezibh-style, with 5 or 6 lenses, and modest negative optical power. They have 2.2°-3° ields of view, with curved
and telecentric focal surfaces suitable for fiber spectroscopy. Some variants also allow wide-field imaging, by changing
the last WFC element. Apart from the adaptation of the Terebizh design for spectroscopy, the key feature is a new
concept for a ‘Compensating Lateral Atmospheric Dispersion Corrector’, with two of the lenses being movable laterally
by small amounts. This provides excellent atmospheric dispersion correction, without any additional surfaces or
absorption. A novel and simple mechanism for providing the required lens motions is proposed, which requires just 3
linear actuators for each of the two moving lenses.
The Anglo-Australian Telescope's 2° field 400 fiber prime focus feed for spectroscopy has been very successful. For a
new instrument proposal (known as Hector) to provide robotically deployed IFUs at the AAT prime focus, a corrector
giving a field 3° in diameter is required to make optimum use of as many as 100 IFUs. Having IFUs with individual
field diameters of 10 to 15 arcsec feeding spectrographs allows some relaxation in the tolerances to lateral chromatic
aberration and to atmospheric dispersion, since each can be compensated computationally without much loss in
efficiency. The AAT has four removable top ends, of which the original prime focus version could be recycled to carry a
much larger corrector. Its outer ring passes a field up to 3.3° diameter without vignetting and the dome slit has a little
more clearance. A very satisfactory optical design has been developed for a corrector providing 3° field diameter
without vignetting, having six elements with three non-spherical surfaces. The diameter of the largest element is 1250
mm. The corrector also works well for direct imaging on a flat field up to 1° diameter.
First light from the SAMI (Sydney-AAO Multi-object IFS) instrument at the Anglo-Australian Telescope (AAT) has
recently proven the viability of fibre hexabundles for multi-IFU spectroscopy. SAMI, which comprises 13 hexabundle
IFUs deployable over a 1 degree field-of-view, has recently begun science observations, and will target a survey of
several thousand galaxies. The scientific outputs from such galaxy surveys are strongly linked to survey size, leading the
push towards instruments with higher multiplex capability. We have begun work on a new instrument concept, called
Hector, which will target a spatially-resolved spectroscopic survey of up to one hundred thousand galaxies. The key
science questions for this instrument concept include how do galaxies get their gas, how is star formation and nuclear
activity affected by environment, what is the role of feedback, and what processes can be linked to galaxy groups and
clusters. One design option for Hector uses the existing 2 degree field-of view top end at the AAT, with 50 individual
robotically deployable 61-core hexabundle IFUs, and 3 fixed format spectrographs covering the visible wavelength range
with a spectral resolution of approximately 4000. A more ambitious option incorporates a modified top end at the AAT
with a new 3 degree field-of-view wide-field-corrector and 100 hexabundle IFUs feeding 6 spectrographs.
We discuss the development of multi-core fiber Bragg gratings (FBGs) to be applied to astrophotonics, more specifically
to near-infrared spectroscopy for ground-based instruments. The multi-core FBGs require over 100 notches to reject the
OH lines in a broad wavelength range (160 nm). The number of cores of the fiber should correspond to the mode number
in the multi-mode fibers and should be large enough to be able to capture a sufficient amount of light from the telescope.
A phase-mask based technique is used to fabricate the multi-core FBGs.
This paper describes the cleaning of M5, one of the four mirrors that make up the Southern African Large Telescope's
Spherical Aberration Corrector. As the top upward-facing mirror in a relatively exposed environment, M5 had
accumulated a considerable amount of dust and dirt during the six years it had been on the telescope. With the corrector
on the ground for re-alignment and testing, we had the opportunity to remove, wash and replace the mirror. Various
cleaning techniques were investigated, including an unsuccessful trial application of First Contact surface cleaning
polymer film - fortunately only to a small region outside the mirror's clear aperture. Ultimately, "drag-wiping" with
wads of cotton wool soaked in a 10g/l sodium lauryl sulphate solution proved highly effective in restoring the reflectivity
of M5's optical surface. Following this success, we repeated the procedure for M3, the other upward-facing mirror in the
corrector. The results for M3 were equally spectacular.
ERASMUS-F is a pathfinder study for a possible E-ELT 3D-instrumentation, funded by the German Ministry for
Education and Research (BMBF). The study investigates the feasibility to combine a broadband optical spectrograph
with a new generation of multi-object deployable fibre bundles. The baseline approach is to modify the spectrograph of
the Multi-Unit Spectroscopic Explorer (MUSE), which is a VLT integral-field instrument using slicers, with a fibre-fed
input. Taking advantage of recent developments in astrophotonics, it is planed to equip such an instrument with fused
fibre bundles (hexabundles) that offer larger filling factors than dense-packed classical fibres.
The overall project involves an optical and mechanical design study, the specifications of a software package for 3Dspectrophotometry,
based upon the experiences with the P3d Data Reduction Software and an investigation of the
science case for such an instrument. As a proof-of-concept, the study also involves a pathfinder instrument for the VLT,
called the FIREBALL project.
We demonstrate for the first time an imaging fibre bundle ("hexabundle") that is suitable for low-light applications in
astronomy. The most successful survey instruments at optical-infrared wavelengths today have obtained data on up to a
million celestial sources using hundreds of multimode fibres at a time fed to multiple spectrographs. But a large fraction
of these sources are spatially extended on the celestial sphere such that a hexabundle would be able to provide
spectroscopic information at many distinct locations across the source. Our goal is to upgrade single-fibre survey
instruments with multimode hexabundles in place of the multimode fibres. We discuss two varieties of hexabundles: (i)
closely packed circular cores allowing the covering fraction to approach the theoretical maximum of 91%; (ii) fused noncircular
cores where the interstitial holes have been removed and the covering fraction approaches 100%. In both cases,
we find that the cladding can be reduced to ~2μm over the short fuse length, well below the conventional ~10λ thickness
employed more generally. We discuss the relative merits of fused/unfused hexabundles in terms of manufacture and
deployment, and present our first on-sky observations.
At the Southern African Large Telescope (SALT), in collaboration with FOGALE Nanotech, we have been testing the recently-developed new generation inductive edge sensors. The Fogale inductive sensor is one
technology being evaluated as a possible replacement for the now defunct capacitance-based edge sensing system.
We present the results of exhaustive environmental testing of two variants of the inductive sensor. In addition to the environmental testing including RH and temperature cycles, the sensor was tested for sensitivity to dust and metals. We also consider long-term sensor stability, as well as that of the electronics and of the glue used to bond the sensor to its supporting structure. A prototype design for an adjustable mount is presented which will allow for in-plane gap and shear variations present in the primary mirror configuration without adversely disturbing the figure of the individual mirror segments or the measurement accuracy.
The AAO is building an optical high resolution multi-object spectrograph for the AAT for Galactic Archaeology. The
instrument has undergone significant design revision over that presented at the 2008 Marseilles SPIE meeting. The
current design is a 4-channel VPH-grating based spectrograph providing a nominal spectral resolving power of 28,000
and a high-resolution mode of 45,000 with the use of a slit mask. The total spectral coverage is about 1000 Angstroms
for up to 392 simultaneous targets within the 2 degree field of view. Major challenges in the design include the
mechanical stability, grating and dichroic efficiencies, and fibre slit relay implementation. An overview of the current
design and discussion of these challenges is presented.
Echidna is a fiber positioner designed and built by the Anglo-Australian Observatory using novel technology
to position 400 fibers in the prime focus field of the Subaru telescope. The fibers feed two near infrared OH-suppression
spectrographs, the whole project being known as Fiber Multi Object Spectrograph (FMOS). In order
to accommodate the large number of the fibers in the physically limited area, a new fiber positioning method is
developed. Stand-alone tests of the positioner at sea level confirm its performance is fully satisfactory. Initial
results and prospects of the on-sky commissioning tests of the positioner are also described.
We highlight the operational challenges and planned solutions faced by an optical observatory taking advantage of the
superior astronomical observing potential of the Antarctic plateau. Unique operational aspects of an Antarctic optical
observatory arise from its remoteness, the polar environment and the unusual observing cycle afforded by long
continuous periods of darkness and daylight. PILOT is planned to be run with remote observing via satellite
communications, and must overcome both limited physical access and data transfer. Commissioning and lifetime
operations must deal with extended logistics chains, continual wintertime darkness, extremely low temperatures and
frost accumulation amidst other challenging issues considered in the PILOT operational plan, and discussed in this presentation.
FMOS: the Fiber Multiple-Object Spectrograph is the next common-use instrument of the Subaru Telescope,
having a capability of 400 targets multiplicity in the near-infrared 0.9-1.8μm wavelength range with a field
coverage of 30' diameter. FMOS consists of three units: 1) the prime focus unit including the corrector lenses,
the Echidna fiber positioner, and the instrument-bay to adjust the instrument focus and shift the axis of the
corrector lens system, 2) the fiber bundle unit equipping two fiber slits on one end and a fiber connector box with
the back-illumination mechanism on the other end on the bundle, 3) the two infrared spectrographs (IRS1 and
IRS2) to obtain 2×200 spectra simultaneously. After all the components were installed in the telescope at the
end of 2007, the total performance was checked through various tests and engineering observations. We report
the results of these tests and demonstrate the performance of FMOS.
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed Australian/European optical/infrared
telescope for Dome C on the Antarctic Plateau, with target first light in 2012. The proposed telescope is 2.4m diameter,
with overall focal ratio f/10, and a 1 degree field-of-view. In median seeing conditions, it delivers 0.3" FWHM wide-field
image quality, from 0.7-2.5 microns. In the best quartile of conditions, it delivers diffraction-limited imaging down
to 1 micron, or even less with lucky imaging. The areas where PILOT offers the greatest advantages are (a) very high
resolution optical imaging, (b) high resolution wide-field optical imaging, and (c) all wide-field thermal infrared
imaging. The proposed first generation instrumentation consists of (a) a fast, low-noise camera for diffraction-limited
optical lucky imaging; (b) a gigapixel optical camera for
seeing-limited imaging over a 1 degree field; (c) a 4K x 4K
near-infrared (1-5 micron) camera with both wide-field and diffraction-limited modes; and (d) a double-beamed midinfrared
(7-40 micron) camera.
AAOmicron is a wide-field, fiber-fed, multi-object, near-infrared spectrograph concept for the Anglo Australian
Telescope (AAT). It is one of a number of instruments concepts (primarily for bright time use) recently considered to
complement the existing instrumentation and in particular the highly popular AAOmega system (primarily dark and grey
time usage). AAOmicron has a two-degree field of view, 240 robotically configured fibers and operates between 0.98
and 1.75μm at a resolution of R~3500. AAOmicron offers a broad suite of applications from the study of low-mass stars,
to determining the structure of the high-redshift Universe. We present an overview of the instrument concept, which is
based heavily on the highly successful AAOmega system, and describe how the AAOmega spectrograph design could be
adapted for near-infrared observations to provide a highly cost effective and scientifically compelling instrument.
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed Australian/European optical/infrared
telescope for Dome C on the Antarctic Plateau, with target first light in 2012. The telescope is 2.4m diameter, with
overall focal ratio f/10, and a 1 degree field-of-view. It is mounted on a 30m tower to get above most of the turbulent
surface layer, and has a tip-tilt secondary for fast guiding. In median seeing conditions, it delivers 0.3" FWHM wide-field
image quality, from 0.7-2.5 microns. In the best quartile of conditions, it delivers diffraction-limited imaging down
to 1 micron, or even less with lucky imaging. The major challenges have been (a) preventing frost-laden external air
reaching the optics, (b) overcoming residual surface layer turbulence, (c) keeping mirror, telescope and dome seeing to
acceptable levels in the presence of large temperature variations with height and time, (d) designing optics that do
justice to the site conditions. The most novel feature of the design is active thermal and humidity control of the
enclosure, to closely match the temperature of external air while preventing its ingress.
As part of the Starbug development, a range of actuator technologies have been prototyped and trialled in the quest to
develop this novel focal plane positioning system. The Starbug concept is a robotic positioning system that deploys
multiple payloads, such as pickoff optics, optical fibres and other possible devices to micron level accuracy over a flat or
curved focal plane. The development is aimed at addressing some of the limitations of other positioning systems to
provide a reliable, cost effective way of positioning multiple payloads in ambient and cryogenic environments. In this
paper we identify the specification and required characteristics of the micro-robotic actuators as applied to the MOMSI
instrument concept, present descriptions of some of the prototypes along with the results from characterisation and
performance tests. These tests were undertaken at various orientations and temperatures as well as using different
The Fiber Multiple-Object Spectrograph for Subaru Telescope (FMOS) is quite large instrument composed of
the prime focus unit, the fiber bundle unit, and the two infrared spectrographs. Among these units, a part of the
prime focus unit and one of the spectrograph were transported from Kyoto University to the Subaru Observatory
in the middle of 2005. We present the optical and the mechanical components of the spectrograph, which was
reassembled on the new floor of the Subaru dome. We also show the preliminary results of the optical alignment
and the cooling test of the instrument at the summit of Mauna Kea.
HyperSuprime is a next generation wide field camera proposed for the 8.3 m Subaru Telescope. The targeted field of view is larger than 1.5 deg in diameter, which will give us roughly 10 times increase of the survey speed compared with the existing prime focus camera (Suprime-Cam). An overview of the current status of the feasibility study is given.
An unsolved problem in astronomical instrumentation is an imaging integral field spectrograph where the user has the freedom to specify arbitrarily complex, contiguous or disjoint regions over the focal plane, rather than a contiguous rectangular field. We present a new concept to solve this problem. Our device allows the user to format the field of view with fibre bundles packed into arbitrary patterns. The field of view is segmented by a large N(N microlens array (e.g. N=1000). This element divides the wavefront into small beams which pass through a metal plate drilled with a grid of holes in the same format as the microlens array. On the reverse side of the grid, hexagonal blocks comprising 67 input fibres are plugged into position on the grid with a pair of sliding "croupier" sticks. The fibred blocks transport the light to the spectrograph. The blocks are held magnetically and the plugging ensures accurate and repeatable registration with respect to the microlens array. The grid plate is micromachined with baffled holes in order to ensure photometric uniformity over the field of view.
OzPoz is the multi-fiber positioner feeding the spectrographs GIRAFFE and UVES from a Nasmyth focus of VLT Unit Telescope 2. Together with GIRAFFE and UVES, it forms the FLAMES facility. FLAMES has been available for observing since successful completion of its science verification in Jan/Feb 2003. An aim of paramount importance in the design and construction of OzPoz was achievement of high reliability with minimal maintenance in the demanding Cerro Paranal VLT environment. Judged by its first 13 months of operation, it has been very successful in this respect, with an average of only 1% of observing time lost to problems; in the last 5 months of this period, the average was less than 0.1%. Of about 360 fibers and fiber bundles fed from deployable buttons on the two field plates, only one has become unusable (through breakage). The time taken to re-configure the fibers on one plate is always less than the exposure time (a minimum of 20 minutes) on the other (observing) plate, so no observing time is lost on that account and the time to interchange the two plates and acquire the new field is only about 5 minutes. The faintness of objects for which useful spectra can be obtained depends on the accuracy with which the sky background can be subtracted and this, in turn, depends on how well the relative spectral transmissions of fibers allocated to sky and to objects can be calibrated. An accuracy of 0.3% rms has been achieved.
AAOmega is a new spectrograph for the existing 2dF and SPIRAL multifibre systems on the Ango-Australian Telescope. It is a bench-mounted, dual-beamed, articulating, all-Schmidt design, using
volume phase holographic gratings. The wavelength range is 370-950nm, with spectral resolutions from 1400-10000. Throughput, spectral coverage, and maximum resolution are all more than doubled compared with the existing 2dF spectrographs, and stability is increased by orders of magnitude. These features allow entirely new classes of observation to be undertaken, as well as dramatically improving
existing ones. AAOmega is scheduled for delivery and commissioning in Semester 2005B.
The Anglo-Australian Observatory's (AAO's) FMOS-Echidna project is for the Fiber Multi-Object Spectroscopy system for the Subaru Telescope. It includes three parts: the 400-fiber positioning system, the focal plane imager (FPI) and the prime focus corrector. The Echidna positioner concept and the role of the AAO in the FMOS project have been described in previous SPIE proceedings. The many components for the system are now being manufactured, after prototype tests have demonstrated that the required performance will be achieved. In this paper, the techniques developed to overcome key mechanical and electronic engineering challenges for the positioner and the FPI are described. The major performance requirement is that all 400 science fiber cores and up to 14 guide fiber bundles are to be re-positioned to an accuracy of 10μm within 10 minutes. With the fast prime focus focal ratio, a close tolerance on the axial position of the fiber tips must also be held so efficiency does not suffer from de-focus. Positioning accuracy is controlled with the help of the FPI, which measures the positions of the fiber tips to an accuracy of a few μm and allows iterative positioning. Maintaining fiber tips sufficiently co-planar requires accurate control in the assembly of the several components that contribute to such errors. Assembly jigs have been developed and proven adequate for this purpose. Attaining high reliability in an assembly with many small components of disparate materials bonded together, including piezo ceramics, carbon fiber reinforced plastic, hardened steel, and electrical circuit boards, has entailed careful selection and application of cements and tightly controlled soldering for electrical connections.
The Fibre Multi-Object Spectrograph (FMOS) for the primary focus
of Subaru Telescope is one of the second generation
instruments, aiming at acquiring spectra of faint objects with
target multiplicity of up to 400. The optimised wavelengths span
from 0.9 to 1.8 microns so as to extend our knowledge of galaxy
formations and evolutions at higher redshifts in a systematic way,
as well as of variety of intriguing near-infrared objects.
On the basis of detailed design of FMOS, actual processes of
fabrication are in progress, and some of critical hardware
components have successfully been developed. In this report,
we present the status of the FMOS project, the results of
developed components, and also instrument control systems such
as the new detector electronics as well the related contol
A wide range of positioning technologies has been exploited to flexibly configure fiber ends on the focal surfaces of telescopes. The earliest instruments used manual plugging, or glued buttons on the focal plane. Later instruments have used robotic fisherman-round-the-pond probes and articulated armsto position fibres, each probe or arm operated by its own motors, or buttons on fiber ends moved by pick-and-place robotic positioners. A positioner using fiber spines incorporating individual actuators operating over limited patrol areas is currently being manufactured and a derivative proposed for future large telescopes. Other techniques, using independent agents carrying the fiber ends about the focal plane have been prototyped. We describe these various fiber positioning techniques and compare them, listing the issues associated with their implementation, and consider the factors which make each of them suitable for a given situation. Factors considered include: robot geometries; costs; inherent limits to the number of fibers; clustering of targets; serial and parallel positioning and reconfiguration times; adaptability to curved focal surfaces; the virtues of on-telescope versus off-telescope configuration of the field, and suitability for the various telescope foci. The design issues include selection of actuators and encoding systems, counterbalancing, configuration of fiber buttons and their associated grippers, interchanging field plates, and the need for fiber retractors. Finally we consider the competing technologies: fiber and reflective image slicer IFUs, multislit masks and reconfigurable slits.
The science case for wide fields on ELTs is well developed and justifies the implementation of 20 arc-minute and larger fields-of-view with seeing-limited performance on a 20 to 30-meter telescope. However, the practical implementation of a wide field can prove to be challenging with classical telescope design when low-thermal emissivity performance is also being optimized. Segmented mirrors assemblies need not be full aperture, axially symmetric structures. Space for secondary, tertiary, and quaternary mirror support structures that do not cross the optical path can be achieved with off-axis mirror assemblies. Barden, Harmer, Claver, and Dey described a 4-mirror, 1-degree FOV 30-meter telescope. We take that concept further with an off-axis approach. Three conic mirrors are required to produce excellent image quality in the 1-degree FOV (diffraction limited across the central few arc-minutes, better than 0.3" imaging performance at the edge of the field). A flat quaternary mirror is utilized both as a beam steering mirror to different instrument ports on the lower side of the telescope and as an adaptive mirror for wind-buffeting and possible ground layer AO correction. The final f/2.2 focal ratio allows the use of an echidna-style fiber positioner for very dense target field acquisition. Extreme AO and Ground Layer AO ports can both be implemented as well. Diffraction characteristics may possibly be improved given the lack of a spider mount for the secondary mirror but will be elliptical rather than circular.
The Echidna multi-object fiber positioner is part of the Fiber Multi-Object Spectrograph (FMOS) project for the prime focus of the Subaru telescope. Given the physical size of the focal plane and the required number of fibers (400), a positioning system based on the Anglo-Australian Observatory's 2dF instrument, that incorporates the placement of magnetic buttons by a single X/Y/Z robot, was considered impractical. Instead, a solution has been developed in which each fiber is mounted on a tilting spine that allows the fiber to be positioned anywhere in a circle of radius 7 mm. Each of the 400 fibers therefore has a fixed "patrol" area in the field of view, with a significant overlap between neighboring spines. A description of a single Echidna spine is presented. Each spine is driven by a quadrant tube piezoelectric actuator (QTP) that, by a ratcheting mechanism, is able to position the fiber to within 10 μm of any coordinate in the corresponding patrol area. Results of positioning tests for eight of the twenty prototype spines reveal better than specification performance, as well as a durability far in excess of the specified lifetime of the instrument.
OzPoz is a multi-fiber positioner to feed spectrographs from a Nasmyth focus of VLT Unit Telescope 2. The concept follows that of the 2dF system on the AAT: a robot re-positions magnetically attached buttons on one of a pair of steel plates while the other plate is observing. But the large scale and the curvature of the VLT Nasmyth focal surface led to the design being very different. Its combination of large moving elements with high precision and the need to survive severe earthquakes presented special challenges. Electrical interlocking of the many functions had to be very comprehensive to minimize risks of damage to the instrument and harm to personnel. Despite the valuable inheritance from 2dF, considerable effort had to be devoted to software to fit the ESO VLT environment and to deal with the complexity of the interacting elements. Integration on the VLT commenced in March 2002, followed by commissioning runs with Giraffe in June, August, and October. Some instrument defects were uncovered during installation and commissioning but none was fundamental and they were readily fixed in between night runs. The time taken to reconfigure a plate, an average of ten seconds/fiber, meets specification and the accuracy of alignment of fiber apertures with stars is limited mostly by the astrometry of target fields.
The Fiber Multi-Object Spectrograph (FMOS) project is an Australia-Japan-UK collaboration to design and build a novel 400 fiber positioner feeding two near infrared spectrographs from the prime focus of the Subaru telescope. The project comprises several parts. Those under design and construction at the Anglo-Australian Observatory (AAO) are the piezoelectric actuator driven fiber positioner (Echidna), a wide field (30 arcmin) corrector and a focal plane imager (FPI) used for controlling the positioner and for field acquisition. This paper presents an overview of the AAO share of the FMOS project. It describes the technical infrastructure required to extend the single Echidna "spine" design to a fully functioning multi-fiber instrument, capable of complete field reconfiguration in less than ten minutes. The modular Echidna system is introduced, wherein the field of view is populated by 12 identical rectangular modules, each positioning 40 science fibers and 2 guide fiber bundles. This arrangement allows maintenance by exchanging modules and minimizes the difficulties of construction. The associated electronics hardware, in itself a significant challenge, includes a 23 layer PCB board, able to supply current to each piezoelectric element in the module. The FPI is a dual purpose imaging system translating in two coordinates and is located beneath the assembled modules. The FPI measures the spine positions as well as acquiring sky images for instrument calibration and for field acquisition. An overview of the software is included.
The Fibre Multi-Object Spectrograph (FMOS) is a second-generation common-use instrument of the Subaru telescope. Under an international collaboration scheme of Japan, UK, and Australia, a realistic design of FMOS has been already in completion, and the fabrications of hardware components have been in progress. We present the overall design details together with the special features of FMOS subsystems, such as the prime focus corrector, the prime focus mechanical unit including fiber positioners, and the near-infrared spectrograph, etc.
The Echidna concept is an attractive solution to performing wide-field spectroscopy in fast beam systems (around F/2.5 or faster) where traditional pick and place multi-fiber positioners are not viable. We introduce a concept design for a 2000+ fiber Echidna-style positioner for the prime focus of a telescope optimized for wide field spectroscopy. A summary of the original 400-fiber Echidna positioner for the Subaru prime focus is presented. The natural extension of this design to a 2000+ fiber system is discussed.
Two proposals currently under development incorporating such a positioner are introduced. The 2250 fiber Ukidna spectrograph is a stellar radical velocity engine for the UK Schmidt telescope at Siding Spring Observatory. More ambitious is the 4000 fiber Kilo-Aperture Optical Spectrograph (KAOS) enabling the 8-m Gemini telescopes with a 1.5° field of view for multi-object spectroscopy. Both instruments offer an order of magnitude increase in spectroscopic survey power compared with current day facilities.
IRIS2 will provide direct imaging and low dispersion spectroscopy on the Anglo-Australian Telescope (AAT) using a 1K by 1K HgCdTe array and be capable of a future upgrade - by installing a new camera - to use a 2K by 2K array. It will be used primarily with the f/8 telescope configuration but can also be used with f/15 and f/36 configurations. The optics will be entirely transmissive with all spherical surfaces. The collimator will have four elements and the camera, five. With a 50mm collimated beam diameter and an f/2.2 camera, the 1K array will provide a field 7.6 arcmin square with pixels equivalent to 0.45 arcsec. If a 2K array is fitted later, an f/4 camera will give an 8.0 arcmin square field with pixels 0.24 arcsec square. Zemax was used to optimize the design as a multi-configuration system, so that a balance was maintained between direct imaging and spectroscopic performance and between the three atmospheric windows. For direct imaging with the f/2.2 camera, a diffraction based calculation indicates the energy inside a circle inscribed within one pixel is always better than 80 percent of that for a diffraction limited system. Particular care was taken to provide good imaging of the telescope pupil onto the cold stop in K.
The aim for a spectrograph feed from the Subaru prime focus is to have 400 fibers. Since the are of the field is only approximately 1/10 that of the 400 fiber two degree field system on the Anglo-Australian Telescope, placement of magnetic buttons by a robot, as done for 2df, was not considered applicable. Instead, a concept has been developed in which each fiber is held on a spine which can be tilted to position its tip anywhere within a circle. With targets randomly scattered over the field and the radial range for each spine equal to the spine pitch, the success rate in reaching targets is acceptably high. At the f/2 focus, a spine tilt of 1/20 radian is just acceptable and requires the spines be 140 mm long. Two basic mechanisms for tilting and holding such a spine have been investigated experimentally. The first uses three commercial miniature linear actuators set parallel and linked to the base of the spine through simple flexures. A prototype has been built and demonstrated to perform satisfactorily. Another approach is to mount the spine ona ball joint and drive it directly in tip and tilt using a bending piezo impact drive. A prototype of this from has been built; initial test are promising.
Design concept of the fiber multi-object spectrograph (FMOS) for Subaru Telescope together with innovative ideas of optical and structural components is presented. Main features are; i) wide field coverage of 30 arcmin in diameter, ii) 400 target multiplicity, iii) 0.9 to 1.8 micrometers near-IR wavelengths, and iv) OH-airglow suppression capability. The instrument is proposed to be built under the Japan-UK-Australia international collaboration scheme.
OzPoz is a multi-fiber positioner which will feed Nasmyth spectrographs on one of ESOs VLT unit telescopes. Its concept follows that of the positioner for the two degree field facility on the Anglo-Australian Telescope. Thus its fibers will be fed from prims housed in buttons which attach magnetically to steel focal plates; a robotic system will position the buttons; and the plates will be interchanged so one can be re-configured while the other is gathering starlight. However, OzPoz has a number of novel features, most notably the use of a pneumatically operated gripper which relies for its accuracy and friction free rotation on air bearings. The robot motions also employ air bearings, with vacuum preloading. The mechanism which exchanges focal plates has been carefully designed to ensure it will survive the maximum likely earthquake on Paranal without significant damage.
We are proposing a new spectrograph (ATLAS) which would revolutionize intermediate-dispersion observations at the AAT. Based on the new technology of volume phase holographic gratings, and using transmission optics, ATLAS offers high throughput and a wide field. It will be ideally situated to extensive surveys of faint objects. It has been designed with a collimated beam diameter of 150 mm, giving resolution (lambda) /(delta) (lambda) up to nearly 10,000 with a 1.5 arcsecond slit and good efficiency. It will be a dual-beam instrument, to maximize observing speed and allow optimized optical coatings to be used. The project is working towards its concept design review which will occur during 2000.
The first 10 meter Keck telescope has been fully scheduled for astronomy since early 1994. Commissioning the initial three instruments and optimizing the primary mirror performance had occupied most of the previous year. Subsequently, considerable effort has been spent on mechanically and electrically improving the dome and shutter. Despite these problems, the percentage of time lost from astronomy to faults has been reasonably low. Although there remains much room for improvement, e.g. in more carefully controlling the dome thermal conditions and maintaining better alignment of the telescope optics in routine operation, the optical performance has been very encouraging. The median image FWHM reported with scientific instruments has been about 0.7 arcsec and there are firm indications that the site, the optics, and the instrumental seeing will allow us to reach a median of about 0.5 arcsec.
The performance goals of the telescope are reviewed and compared with the achieved values. The optical performance is close to the original goals, but our initial observations support evidence from other observatories that Mauna Kea seeing is even better than was assumed in setting the goals; so it is important not to lower our aims. The primary mirror active control system performance is summarized as well as the pointing the tracking performance. The telescope is substantially operational and since January 1994 we have been devoting the majority of nights to astronomical science.
To take full advantage of the superb seeing available at the best sites, it is essential to control the attitude of a telescope with the utmost accuracy. Conventionally, this entails supporting the optical elements with as stiff a structure as is feasible and moving the structure with as precise and as smooth a drive system as can be afforded, using a massive pier as the datum for angular measurement and for reacting drive torques. The problems and costs in this approach increase steeply with telescope size, especially if the requirements for minimizing local seeing degradation lead to the telescope being mounted high above the ground or having minimal protection from wind. Ground transmitted vibration may also be a significant problem on some sites. A better approach is to provide the higher frequency angular corrections by supplementary drives which react against angular inertias, analogous to the reaction wheels used for pointing spacecraft. Then, attaining fast correction of errors, such as those induced by wind, does not require particularly stiff structures and drives between the optical assembly and earth. In fact these links with the earth might, with advantage, be made deliberately compliant to isolate the optics from ground vibration. If, in addition, the higher frequency angular errors are sensed relative to an inertial frame, the need for precision gearing is greatly reduced. Computer simulations indicate that the inertial drive technique is quite practical. For very large telescopes, this approach offers better performance at substantially lower overall cost than when conventional drives are used alone.
The optical configurations adapted for the IR Imaging Spectrometer (IRIS) designed for AAT are described together with the mechanical design of the spectrometer. The direct imaging of IRIS will provide a number of different angular scales and corresponding fields, with remotely controlled field selection amongst a subset of these. With the widest field, each 0.06-mm pixel will be 2 arcsec; with the narrowest field, it will be about 0.1 arcsec square. The IRIS will be used at both the f/15 and f/36 Cassegrain foci, for the wide-field imaging and the spectroscopy, respectively. Diagrams of optical configurations and the mechanical assembly of IRIS are presented.