This paper deals with the optical design and preliminary optomechanical tolerances of HRIC, the High Resolution Imaging Channel of the SIMBIO-SYS instrument, selected as part of the scientific payload for the ESA cornerstone BepiColombo mission to Mercury. Under the lead of Italy (Principal Investigator: E. Flamini), the project is based on an international co-operation with Institutes from France and Switzerland. Starting from the stringent scientific requirement of 5m ground pixel scale at 400 km from the planet surface, a robust optical design based on a catadioptric Ritchey-Chretien configuration modified with a dedicated corrector camera has been achieved. The optimized configuration is convenient in terms of image quality, number of optical elements, and total length. The channel guarantees a corrected FoV of about 1.5° and allows the achievement of the required resolution with a detector of 2k × 2k pixels. The telescope is diffraction limited, thanks to its focal ratio (F/8), and shows an optimised radiometric flux within the operative spectral range (400 - 900 nm). The channel is equipped with one panchromatic and 3 selective filters. The operation plan foresees the coverage of at least 20% of the whole Hermean surface with the HRIC. The preliminary optomechanical tolerances and the corresponding image quality have been analyzed. Further thermo-mechanical analysis is in progress, which is being analyzed by means of ray-tracing tools for image quality evaluation.
This paper shows the optical transmission evaluated for the two manufactured optical correctors of VST telescope. It
reports the external transmission curves and corresponding data values for the two correctors camera which have been
designed from Technology Working Group at INAF Astronomical Observatory of Capodimonte in Napoli in
collaboration with ESO and realized by Zeiss as part of the whole telescope optical design. The transmission for two-lens
corrector and ADC and one-lens corrector, has been analyzed in the wavelength ranges of measured Zeiss AR coating
curves. The specifications for antireflection coating of optical components of VST correctors have been given on a wide
range (320 ÷ 1014 nm). The transmission curves have been computed at different fields of view positions from the
center, in order to analyze if there were significant differences with components glass thickness variation. The
transmission values reported will be of reference for the phases of test of the correctors mounted at telescope at Paranal
and for the correlated tests and commissioning of the telescope with focal plane camera OMEGACAM.
This paper is about VST active optics system design, specifications and status. The VST is a modified Ritchey-Chretien wide field Alt-Az telescope with a corrector camera (1 square degree field of view), so when all optical components are correctly aligned, only residual aberrations in whole field are present. The major amounts of these aberrations can be introduced by gravitational and thermo opto-mechanical deformations and mirror misalignments. For these reasons active control of the primary mirror shape and secondary mirror position are required to lessen optical aberrations. The aim of active optics is to correct all optical telescope errors in order to make them small compared with external seeing. The VST is essentially compensated for static or slow frequency deformations and misalignments with a band pass from dc to 1/30 Hz, since the corresponding integration time is sufficient to integrate out the external seeing, giving a round image corresponding to the integrated external seeing quality. VST decentering, coma and defocus are corrected by mean of a secondary mirror position control system (a two-stage hexapode system) and spherical, astigmatism, quad-astigmatism and tri-coma are corrected by mean of M1 mirror shape deformation (axial and radial support system). For optical aberrations and guiding measurement an optical sensing arm has been designed.
This paper describes the optical design criteria and expected image quality of the High Resolution Imaging Channel (HRIC), which is part of the Spectrometers and Imagers for Mercury Planetary Orbiter (MPO) BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) suite, for imaging and spectroscopic investigation of Mercury. SIMBIO-SYS has been selected by ESA as part of the scientific payload of the ESA BepiColombo mission to Mercury. HRIC has the main objective of characterising Mercury surface features with a very high spatial resolution in the visible. The optical design has been optimised to achieve the stringent scientific requirement of 5 m ground pixel size at 400 km from the planet surface. The adopted catadioptric optical configuration provides a resolution of 2.5"/pixel for a pixel size of 10 micron. The focal ratio is F#8 in order to be diffraction limited at 400 nm and to optimise radiometric flux and overall mechanical dimensions. The optical design solution includes two hyperbolic mirrors optimized with a dioptric camera, in order to correct the field of view of 1.47°, covered by a detector of 2k x 2k pixels. The mixed (reflective + refractive) solution guarantees a good balance of achieved optical performances and optimisation of resources (mainly volume and mass). The adopted configuration corrects and transmits well over the whole band of observation (400 - 900 nm).
This paper concerns optomechanics tolerances specifications for VST telescope. It shows the strategy of tolerances definition for optomechanical systems. These prescriptions are the baseline for development and tests of VST telescope optomechanic components. The telescope is provided with an active optics control system, so some tolerances may be relaxed, respect to passive systems designs since they can be actively compensated. Gravitational and thermal deformations have been also considered. The design error budget strategy is described. Manufacturing, mounting and alignment tolerances have been evaluated within the whole telescope image quality error budget, in terms of rms spot radius. Since the telescope is seeing limited, effects of atmospheric seeing have also been considered in the error budget in terms of CIR. Do to its large field of view (1 degree square), the VST optical design (optomechanics tolerances included) is the first source of error if compared to a classical telescope design that has a small field of view. The overall optical quality depends also on telescope configuration (ADC and one-lens corrector or two-lens corrector configuration) and on observational zenith angle (0÷50°).
The effects of atmospheric differential refraction on astrophysical measurements are well known. In particular, as a ray of light passes through the atmosphere, its direction is altered by the effects of atmospheric refraction. The amount of this effect depends basically on the variation of the refractive index along the path of the ray. The real accuracy needed in the atmosphere model and in the calculation of the correction to be applied is of course, considerably worse, especially at large zenith angles. On the VLT Survey Telescope (VST) the use of an Atmospheric Dispersion Corrector (ADC) is foreseen at a wide zenith distance range. This paper describes the software design and implementation aspects regarding the analytical correction law discovered to correct the refraction effect during observations with VST.
This paper shows criteria and strategy followed for the optics design of VST telescope, and foreseen image quality. The optics design has been optimized in order to achieve the high required image quality on the base of main scientific requirements, mechanics constraints coming from the wide CCD mosaic camera and dimensional requirements. Manufacturing reliability integrated operational efficiency, and costs optimization criteria have been also taken into account. The VST optics has been designed in order to have a 2.61 m Alt.az telescope operating from U to I bands with an excellent image quality (80% of Encircled Energy enclosed in less than two pixels) on a wide field of view (1° x 1°). The telescope will have a very high resolution (0.21"/pixel) with a pixel size of 15 μm;. The peculiarity of VST optics design is that telescope configuration is not a pure Ritchey - Chretien, but it is integrated with two different refracting correctors in order to minimize residual field aberrations. One corrector is optimized for observations at small zenith angles (U-I bands), while the other one includes an ADC providing high quality images until zenith angles of 50° (B-I bands). This corrector is a very useful and innovative integrated facility. The optics is being manufactured from Zeiss/LZOS. The telescope is going to be mounted in Napoli before shipment to Chile where it will be installed near the giants VLT units and will be a dedicated wide field imaging facility operating in narrow and wide visible bands
The VLT Survey Telescope (VST) is a cooperative program between the European Southern Observatory (ESO) and the INAF Capodimonte Astronomical Observatory (OAC), Naples, for the study, design, and realization of a 2.6-m wide-field optical imaging telescope to be operated at the Paranal Observatory, Chile. The VST has been specifically designed to carry out stand-alone observations in the UV to I spectral range and to supply target databases for the ESO Very Large Telescope (VLT). The telescope design, manufacturing and integration are responsibility of OAC. The telescope is in Cassegrain configuration and for this reason the primary mirror cell represents one of the most complex telescope subsystems, designed to host a large amount of auxiliary sub-systems and to support a wide field camera. The paper describes the solutions adopted as a result of an integrated optimized optical and mechanical design.
The VST (Very Large Telescope Survey Telescope) is an 2.6 m class Alt-Az telescope which will be installed in the European Southern Observatory (ESO) Paranal site, Chile. It has been designed by the Technology Working Group of the Astronomical Observatory of Capodimonte, Italy. The VST is an 1 degree(s) X 1 degree(s) wide-field imaging facility planned to supply databases for the ESO VLT science and carry out stand-alone observations in the UV to I spectral range starting in the year 2001. All the solutions adopted in the VST design comply to the ESO VLT standards. This paper reports a technical overview of the telescope design.