This paper presents three optical designs based on the work of Maurice Paul. Paul's three-mirror anastigmats produce well-corrected, distortion-free fields of view. His design equations can be solved for a spherical primary mirror with one limitation: the image field is curved. Adding all-spherical refractive field-flattening optics yields well-corrected, flat image-fields of two degrees angular diameter or more. These designs can be scaled to very large telescopes with current technology.
The Korea Astronomy and Space Science Institute (KASI) are under development three 1.6m optical telescopes for the
Korea Micro-lensing Telescope Network (KMTNet) project. These will be installed at three southern observatories in
Chile, South Africa, and Australia by middle 2014 to monitor dense star fields like the Galactic bulge and Large
Magellanic Cloud. The primary scientific goal of the project is to discover numerous extra-solar planets using the
gravitational micro-lensing technique. We have completed the final design of the telescope. The most critical design
issue was wide-field optics. The project science requires the Delivered Image Quality (DIQ) of less than 1.0 arcsec
FWHM within 1.2 degree radius FOV, under atmospheric seeing of 0.75 arcsec. We chose the prime-focus configuration
and realized the DIQ requirement by using a purely parabolic primary mirror and four corrector lenses with all spherical
surfaces. We present design results of the wide-field optics, the primary mirror coating and support, and the focus system
with three linear actuators on the head ring.
We present the as-built design overview and post-installation performance of the upgraded WIYN Bench Spectrograph.
This Bench is currently fed by either of the general-use multi-fiber instruments at the WIYN 3.5m telescope on Kitt
Peak, the Hydra multi-object positioner, and the SparsePak integral field unit (IFU). It is very versatile, and can be
configured to accommodate low-order, echelle, and volume phase holographic gratings. The overarching goal of the
upgrade was to increase the average spectrograph throughput by ~60% while minimizing resolution loss (< 20%). In
order to accomplish these goals, the project has had three major thrusts: (1) a new CCD was provided with a nearly
constant 30% increase is throughput over 320-1000 nm; (2) two Volume Phase Holographic (VPH) gratings were
delivered; and (3) installed a new all-refractive collimator that properly matches the output fiber irradiance (EE90) and
optimizes pupil placement. Initial analysis of commissioning data indicates that the total throughput of the system has
increased 50-70% using the 600 l/mm surface ruled grating, indicating that the upgrade has achieved its goal.
Furthermore, it has been demonstrated that overall image resolution meets the requirement of <20% loss.
The One Degree Imager will be the future flagship instrument at the WIYN 3.5m observatory, once commissioned in
2011. With a 1 Gigapixel focal plane of Orthogonal Transfer Array CCD devices, ODI will be the most advanced optical
imager with open community access in the Northern Hemisphere. In this talk we will summarize the progress since the
last presentation of ODI at the SPIE 2008 meeting, focusing on optics procurement, instrument assembly and testing, and
The WIYN consortium is building the One Degree Imager (ODI) to be mounted to a Nasmyth port of the WIYN 3.5m
telescope, located at Kitt Peak, Arizona (USA). ODI will utilize both the excellent image quality and the one-degree
field of view that the telescope delivers. To accommodate the large field of view (~0.39m diameter unvignetted field
with 0.54m across the diagonal of the one-degree-square, partially vignetted field), 0.6m-class optics are required. The
ODI design consists of a two element corrector: one serves as a vacuum barrier to the cryostat, the other is an asphere;
two independently rotating bonded prism pairs for atmospheric dispersion compensation (ADC); nine independently
deployable filters via a simple pivoting motion; and a 971 mega-pixel focal plane consisting of 64 orthogonal transfer
array (OTA) devices.
This paper is an overview of the mechanical design of ODI and describes the optical element mounting and alignment
strategy, the ADC & filter mechanisms, plus the focal plane. Additionally, the project status will be discussed.
In accompanying papers Jacoby1 describes ODI's optical design, Yeatts2 describes the software and control system
design, and Harbeck3 gives a general update on the project.
The main advantage of the WIYN One Degree Imager (ODI) over other wide-field imagers will be its exceptional image quality. The fine pixel scale (0.11") provides uncompromised sampling of stellar PSFs under most conditions (seeing >0.3"). The telescope routinely delivers the site seeing (median ~ 0.7") which is often below 0.5" FWHM, and can be as low as 0.25". The ODI specifications require the optics to maintain native high quality images. A two-element, fused silica, corrector meets the geometric error budget of 0.10" images, but the first element requires a mildly aspheric surface. The other element serves as the dewar window. A pair of cemented prisms (fused silica plus PBL6Y) serve as an ADC, which is essential to meet the image quality requirements for many observing programs. We describe the optical design details and its performance, the tolerances required, and the trade-offs considered for anti-reflection coatings. This paper is an update to a preliminary three-element design.
A thermal model of the Discovery Channel Telescope (DCT) was used to estimate the contribution of major sources of
local seeing; shell seeing, dome seeing and mirror seeing. The model simulates a dynamic equilibrium over several
day/night cycles taking into account the morphology of the facility, diurnal insolation and radiation to the night sky,
local air temperature and humidity swings, wind and air flow through the facility, and infiltration from warm spaces
within the facility. The model confirmed that the well ventilated design of the DCT facility will virtually eliminate
dome seeing, but that shell seeing and mirror seeing could be major contributors to local seeing. These can be mitigated
by the choice of an appropriate exterior coating, and by cooling the primary mirror.
We describe the redesign and upgrade of the versatile fiber-fed Bench Spectrograph on the WIYN 3.5m telescope. The
spectrograph is fed by either the Hydra multi-object positioner or integral-field units (IFUs) at two other ports, and can
be configured with an adjustable camera-collimator angle to use low-order and echelle gratings. The upgrade, including
a new collimator, charge-coupled device (CCD) and modern controller, and volume-phase holographic gratings
(VPHG), has high performance-to-cost ratio by combining new technology with a system reconfiguration that optimizes
throughput while utilizing as much of the existing instrument as possible. A faster, all-refractive collimator enhances
throughput by 60%, nearly eliminates the slit-function due to vignetting, and improves image quality to maintain
instrumental resolution. Two VPH gratings deliver twice the diffraction efficiency of existing surface-relief gratings: A
740 l/mm grating (float-glass and post-polished) used in 1st and 2nd-order, and a large 3300 l/mm grating (spectral
resolution comparable to the R2 echelle). The combination of collimator, high-quantum efficiency (QE) CCD, and VPH
gratings yields throughput gain-factors of up to 3.5.
This paper describes the studies performed to establish a baseline conceptual design of the Segment Support Assembly
(SSA) for the Thirty Meter Telescope (TMT) primary mirror. The SSA uses a combination of mechanical whiffletrees
for axial support, a central diaphragm for lateral support, and a whiffletree-based remote-controlled warping harness for
surface figure corrections. Axial support whiffletrees are numerically optimized to minimize the resulting gravityinduced
deformation. Although a classical central diaphragm solution was eventually adopted, several lateral support
concepts are considered. Warping harness systems are analyzed and optimized for their effectiveness at correcting
second and third order optical aberrations. Thermal deformations of the optical surface are systematically analyzed
using finite element analysis. Worst-case performance of the complete system as a result of gravity loading and
temperature variations is analyzed as a function of zenith angle using an integrated finite element model.
The Thirty Meter Telescope (TMT) project is a partnership between ACURA, AURA, Caltech, and the University of California. The design calls for a 3.6 m diameter secondary mirror and an elliptical tertiary mirror measuring more than 4 m along its major axis. Each mirror will weigh more than two metric tons and must be articulated to compensate for deformation of the telescope structure. The support and control of these "smaller optics" pose significant challenges for
the designers. We present conceptual designs for active and passive figure control and articulation of these optics.
Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.
We present results from a study of the performance of the MMT
thermal system. The 6.5-m MMT primary mirror consists of a
borosilicate honeycomb structure that is thermally controlled with
a forced-air ventilation system. We will give an overview of both
the measurement and control systems. Our goal is to define an
algorithm for control of the ventilation system such that the
primary mirror temperature closely tracks ambient while minimizing
thermal gradients. Future work will include a study of correlations
between the thermal state of the primary mirror and both seeing and
wavefront errors. The thermal system is currently controlled by
the telescope operators, but the results from this work will assist in fully automating the system.
The Gemini Laser Launch Telescope will reside behind the secondary support structure of the Gemini 8m telescope, where it will expand an incoming sodium laser beam to 450 mm diameter and launch it into the sky, co-axial to the main telescope. The tight space and stringent performance specifications have required some innovative approaches in optical and mechanical design.
We describe a multi-element refractive corrector for the prime focus of the proposed Lowell four-meter telescope. The design provides sub-half arcsecond images over a two-degree field of view, with a flat image surface and images that are confocal across a broad wavelength band covering the U to I spectral range. Initial studies cover the feasibility of fabrication and explore the possibility of a simple atmospheric dispersion corrector.
Segmented mirror telescopes take advantage of modular design to achieve large apertures at low cost. This paper describes the segment mount developed for the Southern African Large Telescope. The mount provides passive precision support for the optics, kinematic registration to the primary mirror truss, precision tip-tilt and piston adjustments, and interchangeability between segments and mounts. A trial production run of mounts is now in fabrication prior to full production of 91 units needed to populate the SALT primary.
Seeing is generally caused by non-homogeneous variations in the refractive index of the column of air in the observed light path. The refractive index is affected by wavelength, air pressure, temperature and relative humidity. In this paper the Cauchy-Lorenz formula for the refractive index of air is evaluated to find the relative dependence of seeing on each of these parameters. A standard atmospheric model is used to evaluate the effect of altitude on each term, and from this an expression for the variation of seeing as a function of altitude is derived.
The WIYN 3.5 meter telescope uses active thermal control of the primary mirror and both active and passive ventilation of the observatory enclosure. These features have proven effective for delivering consistently excellent images, and make the WIYN facility an ideal test bed for quantitative measurements of the effects of temperature and ventilation on mirror and dome seeing. We describe the results of seeing experiments conducted over the first four years of operations at the WIYN Observatory.
In the year 2000, EOS Technologies, Inc. of Tucson, Arizona will complete six two-meter class telescopes for astronomy. Applications for these telescopes range from monitoring of active-galactic nuclei to the search for extra-solar planets. Four of the telescopes will form part of the Keck International Project. These telescopes meet the highest tracking and axis interaction specifications ever attempted in a two-meter class telescope. Each of these telescopes is capable of fully remote-control and semi-autonomous operation.
The Vatican Advanced Technology Telescope incorporates a fast (f/1.0) borosilicate honeycomb primary mirror and an f/0.9 secondary in an aplanatic Gregorian optical configuration. We provide a brief technical and performance overview by describing the optical layout, the primary and secondary mirror systems, and the telescope drive and control system. Results from a high resolution wavefront sensor and a current wide-field image taken at the f/9 focus demonstrates the overall fine performance of the telescope.
In this paper we describe the active optics system of the WIYN 3.5 meter telescope put into operation in the spring of 1995 on Kitt Peak, Arizona. The active optics system provides real time collimation of the telescope and optical figure control of the primary mirror. The individual subsystems are first described. These include the wavefront curvature sensing technique, the support and articulation of the secondary mirror, the control of the primary mirror figure and rigid body motion, and the mechanics and electronics used for controlling and monitoring the optics. Algorithms for the complete loop are then discussed. This involves mapping coma terms used to actively correct the collimation, while residual phase errors are corrected by active control of the forces supporting the primary mirror. In the next section we compare two operational modes: open loop using mapped collimation and optical figure corrections, and closed loop using feedback from the wavefront sensor directly. Finally, preliminary stellar images obtained with the actively controlled telescope are presented.
The WIYN 3.5 Meter Telescope enclosure was designed to minimize the effects of dome seeing. A combination of strategies is being used to achieve this goal including a well ventilated telescope chamber, low thermal inertia construction, active ventilation using fans, and utilization of surface coatings to control radiation losses. This paper presents the design approach and preliminary thermal measurements of the facility.
The WIYN Observatory is a joint project of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatories to build a 3.5 meter ground-based telescope on Kitt Peak, Arizona. The observatory is currently under construction and nearing completion. This paper presents the current status of the project.
The project to enlarge the Multiple Mirror Telescope (MMT) to a 6.5 m single primary mirror telescope is described. The goal is to provide a telescope which is competitive with the existing MMT in tracking and pointing performance (0.2 and 1.0 arcseconds, respectively) but has more than twice the light gathering power and 15 times the angular field of view. The existing mount and building will be used with minor modifications so that the cost of the project is relatively modest. Casting of the 6.5 m mirror is scheculed in early 1991 and first light in late 1993.
The Vatican Advanced Technology Telescope (VATT) now being fabricated differs from traditional telescopes in many ways. The altitude over azimuth mount will be direct driven by large diameter motors. The cell for the f/1 borosilicate honeycomb primary mirror incorporates a thermal control system to stabilize the mirror temperature. The f/9 Gregorian secondary will be mounted on a six-axis stage and controlled to submicron resolution in order to maintain the strict collimation tolerances needed for the fast optical system. Though only 1.83 m in aperture, VATT incorporates many of the design features of larger projects in the 8 m class.