Telescopes with unobstructed pupil are known to deliver clean point spreadfunction (PSF) to their focal plane, in contrast to traditional telescopes withobstructed pupil. Recent progress in the manufacturing aspheric surfaces andmounting accuracy favors unobstructed telescopes over obstructed telescopes forscience cases that demand stable and clean PSF over the entire field-of-view.In this paper we compare the image quality of an unobstructedThree-Mirror-Anastigmat (TMA) design with that of an obstructed TMA. Both thedesigns have the same primary mirror, effective focal length, field-of-view anddetector characteristics. We demonstrate using simulated images of faintelliptical galaxies imaged through the two designs, that both the designs canmeasure morphological parameters with same precision, if the PSF isreconstructed within 12 arc-minutes of the source. We also demonstrate that,the unobstructed design delivers desirable precision even if the PSF isreconstructed 50 arc-minutes away from the source. Therefore the PSF ofunobstructed design is uniform over a wider field-of-view compared to anobstructed design. The image quality is given by the 1$\sigma$ error-bars (68%confidence level) in the fitted values of the axis-ratio and position-angle ofthe simulated galaxies.
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