THE SCIENTIFIC POTENTIAL OF DIFFRACTION-LIMITED IMAGING FROM MID-LATITUDE ULTRA-LONG DURATION BALLOON PAYLOADS IS IMMENSE. THE COMBINATION OF DIFFRACTION-LIMITED ANGULAR RESOLUTION EXTREME STABILITY SPACE-LIKE BACKGROUNDS AND LONG INTEGRATIONS ENABLES TRANSFORMATIVE OPPORTUNITIES IN STUDIES RANGING FROM THE WEAK LENSING OF GALAXY CLUSTERS AND COSMIC SHEAR TO THE SEARCH FOR EXOPLANETS. PIONEERING RESEARCH SPEAR-HEADED BY THE CO-INVESTIGATORS OF THIS PROPOSAL HAS LED TO THE DEVELOPMENT OF THE PRECISION TIP/TILT AND DE-ROTATION SYSTEMS THAT ARE REQUIRED TO REALIZE THE POTENTIAL OF THE SUPER-PRESSURE BALLOON (SPB) PLATFORM FOR DEEP WIDE-FIELD IMAGING.UNDER A SEPARATELY FUNDED CANADIAN SPACE AGENCY PROGRAM A HALF-METER CLASS TELESCOPE HAS BEEN INTEGRATED WITH A PROTOTYPE SUB-ARCSECOND POINTING SYSTEM. WE PROPOSE A HIGHLY FOCUSED FIVE-YEAR PROGRAM TO DEVELOP AND FLY A COMPARABLE INSTRUMENT ON THE MID-LATITUDE SPB PLATFORM DEMONSTRATING THE IMAGING CAPABILITY DURING AN ULTRA-LONG DURATION BALLOON FLIGHT WHILE PROVIDING SPACE-QUALITY WEAK LENSING MEASUREMENTS FOR A LARGE CATALOG OF GALAXY CLUSTERS. THIS INSTRUMENT WILL PROVIDE IMAGING WITH A HALF-DEGREE FIELD OF VIEW AND 0.3-ARCSECOND RESOLUTION IN FIVE BANDS BETWEEN 300 AND 1000 NM WITH SENSITIVITIES IN THE SHAPE-BAND EXCEEDING 24TH MAGNITUDE (&GT;5 SIGMA) IN 300 SECONDS OF INTEGRATION.WE PROPOSE AN OBSERVING SCHEDULE THAT IS SPLIT BETWEEN A PERFORMANCE VERIFICATION SAMPLE A PHOTOMETRIC AND SPECTROSCOPIC CALIBRATION SET A DEEP FIELD AND A SCIENCE CATALOG. THE PERFORMANCE VERIFICATION SET PRIORITIZES A SAMPLE OF THIRTY CLUSTERS THAT HAVE BEEN PREVIOUSLY WELL STUDIED WITH THE HST ADVANCED CAMERA FOR SURVEYS THE CHANDRA X-RAY OBSERVATORY AND FOR WHICH THERE ARE COMPTON-Y PARAMETER DATA FROM MILLIMETER WAVELENGTHS. THE PHOTOMETRIC CALIBRATION SET WILL BE SELECTED FROM THE COSMOS FIELD. THE SCIENCE CATALOG WILL DRAW FROM A SET OF MORE THAN 150 SUNYAEV-ZEL'DOVICH X-RAY AND OPTICALLY-SELECTED CLUSTERS SPANNING A WIDE RANGE OF CLUSTER MASSES AND MORPHOLOGIES. ASIDE FROM DEMONSTRATING THE TECHNICAL APPROACH THESE DATA WILL ENABLE A SYSTEMATIC PROGRAM TO CONSTRAIN THE MASS-OBSERVABLE RELATIONS OVER AN UNPRECEDENTED SCALE.THIS PROPOSAL LEVERAGES THE EXPERIENCE AND CAPABILITIES OF THE JPL TORONTO PRINCETON AND DURHAM GROUPS. A SUCCESSFUL DEMONSTRATION OF THE TECHNICAL APPROACH AND THE SCIENTIFIC POTENTIAL WILL MOTIVATE FUTURE DEVELOPMENT OF FACILITY-CLASS INSTRUMENTS ON THE SPB PLATFORM.