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An extremely wide field imager/spectrograph for LBT. Roberto Ragazzoni, Jacopo Farinato, Emiliano DIolaiti, Giorgia Gentile, Carmelo Arcidiacono, Renato Falomo, Adriano Fontana, Bianca Poggianti, Emanuele Giallongo INAF – Padova, Bologna and Roma Observatories July 8 th , 2008

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## An extremely wide field imager/spectrograph for LBT

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**An extremely wide field imager/spectrograph for LBT**Roberto Ragazzoni, Jacopo Farinato, Emiliano DIolaiti, Giorgia Gentile, Carmelo Arcidiacono, Renato Falomo, Adriano Fontana, Bianca Poggianti, Emanuele Giallongo INAF – Padova, Bologna and Roma Observatories July 8th, 2008 Next generation science for LBT**An extremely wide field imager/spectrograph for LBT**…actually a 3x3degree or 3deg in DIAMETER… Roberto Ragazzoni, Jacopo Farinato, Emiliano DIolaiti, Giorgia Gentile, Carmelo Arcidiacono, Renato Falomo, Adriano Fontana, Bianca Poggianti, Emanuele Giallongo INAF – Padova, Bologna and Roma Observatories July 8th, 2008 Next generation science for LBT**Scaling factors…**• We are in the transition to ELT era… • …so we should be used to break the factor 2 syndrome… • We want a FoV 3deg in diameter rather than a 0.5deg one… • …that is 36 times more FoV then LBC… • …or it is 9x4=36 times again more photons than a 1deg on a 4m telescope! • We want it with MOS capabilities…**Scaling factors…**• In 1984 Richardson et al. wrote a paper on the scaling subject… • Size of the first lens scales linearly with the FoV… • …leading to a 4.9m lens for a 3degs Prime Focus… • weighting about 100tons!**Surprised????**5.0m**Would you really allow this person**to do a WFoV camera for you??? Size compared with a normal (???) man… And still the refractive part of the camera remains even more difficult and challenging as what we call a “conventional” Prime Focus…!!!**What is difficult in a W-FoV imager?**• The fast focal ratio (smaller than the Cassegrain stations) Prime Focus or Focal reducer • Wide Field of View (a tautology??) use big optics • Correction of off-axis aberration Several optical elements to control aberrations (with aspheric too) • A large array or mosaic Big buttable CCDs**What is difficult in a W-FoV imager?**• The fast focal ratio (smaller than the Cassegrain stations) Prime Focus or Focal reducer • Wide Field of View (a tautology??) use big optics • Correction of off-axis aberration Several optical elements to control aberrations (with aspheric too) • A large array or mosaic Big buttable CCDs**If the FoV is really small (e.g. 1arcmin) the optics is**easy… and the aberration of the telescope within such a FoV change so little that one can place in the pupil an aberration corrector and only residuals over such a small FoV will appears. So you can think to place this off-axis…**An array of these devices**• Is made by: • Two lenslets • A plate with slightly different • pupil aberrations, each for FoV • (maybe they can be grouped if • the telescope aberration change • slightly over a few arcmin) • A lot of small, non buttable, CCDs Please note: with the same FoV and F/ the amount of silicon surface is the same, but splitted into several pieces (quality of selected small surfaces is easier!)**Short F/ focal plane**Long F/ focal plane Just an explanatory picture**Pupil aberration correctors**• Made by two equal components whose aberration is denoted by a vector…**Pupil aberration correctors**• Made by two equal components whose aberration is denoted by a vector…**Pupil aberration correctors**• Made by two equal components whose aberration is denoted by a vector…**Pupil aberration correctors**• Made by two equal components whose aberration is denoted by a vector…**Pupil aberration correctors**• Made by two equal components whose aberration is denoted by a vector…**Multi Object Spectroscopy too!!**• The physical size where fibers are to be located is much smaller than the mechanical size where the positioner is to be placed • Ideal condition for mechanical solutions (almost doable with off-the-shelf components) • Ratio of size is ratio between long and short focal ratios (2 to 5, in our designs) • Array of small FOSC spectroscopic cameras F/4 F/2 F/3**Toward a modular camera concept**A combination of modules**Massive production**Lenslets and CCDs are the same for the whole camera while pupil correctors are different. The difference in the pupil correctors can be limited to the way of mounting different kind of plates wrt the optical axis or wrt themselves. A 4x4 module**A few notes**• If aberration is large at the edge some light coming from the same source will spill into adjacent lenslets • The CCDs should be slightly over-sized in order to do not loose any photon • If aberrations change a lot at the edge the pitch of lenslet can be coarser to the center and finer at the edges • Some “lenslets” have to be devoted to Active Optics wavefront sensing**Sub-apertures size can**be variable on the FoV…**0.5deg**3deg (+dedicated M2…) Focal station: Nasmyth Size: ~1.5m x 1,5m x 0.3m Focal station: Prime Size: ~1m x 1m x 1.5m Focal reducer at Nasmyth [also spectrograph!] Size ! 5x5x5m ??? Or simply undoable for 3degs**Filter issue**• Big filters in long F/ arm (input to the module) always possible • Interchangeable filters for each CCD is painful… • Set of filters changeable on night to night (or longer) basys is doable • Naturally survey-oriented instrument…**The concept…**• A trapped about F/4 Cassegrain with a 2.7m diameter secondary dedicated mirror • About 1000 small camera each with a few slits • CCDs can be read in a fast mode in parallel (astrocinematography) • Modules for imaging and MOS interchangeable and reconfigurable night to night**Status**References • Developing a preliminary optical design to be used as baseline for a consistent optomechanical study • Preliminary optical designs in the subarcsec area • Aiming to match the LBC optical quality, that sounds doable • A looot of space parameters to explore… • SPIE proc.6272, 25 (2006) • SPIE proc.6269, 187 (2006) • SPIE proc.5492, 121 (2004) • A napkin on a “restaurant” in Copenhagen (2002)

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