The impact of camera optical alignments on weak lensing measures for the Dark Energy Survey

Michelle L. Antonik, David J. Bacon, Sarah Bridle, Peter Doel, David Brooks, Sue Worswick, Gary Bernstein, Rebecca Bernstein, Darren DePoy, Brenna Flaugher, Joshua A. Frieman, Michael Gladders, Gaston Gutierrez, Bhuvnesh Jain, Michael Jarvis, Stephen M. Kent, Ofer Lahav, S. -J. Parker, Aaron Roodman, Alistair R. Walker

Research output: Contribution to journalArticlepeer-review


Telescope point spread function (PSF) quality is critical for realizing the potential of cosmic weak lensing observations to constrain dark energy and test general relativity. In this paper, we use quantitative weak gravitational lensing measures to inform the precision of lens optical alignment, with specific reference to the Dark Energy Survey (DES). We compute optics spot diagrams and calculate the shear and flexion of the PSF as a function of position on the focal plane. For perfect optical alignment, we verify the high quality of the DES optical design, finding a maximum PSF contribution to the weak lensing shear of 0.04 near the edge of the focal plane. However, this can be increased by a factor of approximately 3 if the lenses are only just aligned within their maximum specified tolerances. We calculate the E- and B-mode shear and flexion variance as a function of the decentre or tilt of each lens in turn. We find tilt accuracy to be a few times more important than decentre, depending on the lens considered. Finally, we consider the compound effect of decentre and tilt of multiple lenses simultaneously, by sampling from a plausible range of values of each parameter. We find that the compound effect can be around twice as detrimental as when considering any one lens alone. Furthermore, this combined effect changes the conclusions about which lens is most important to align accurately. For DES, the tilt of the first two lenses is the most important.
Original languageEnglish
Pages (from-to)3291-3300
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date10 Apr 2013
Publication statusPublished - Apr 2013


  • gravitational lensing: weak
  • methods: data analysis
  • techniques: image processing
  • cosmology: observations
  • dark energy
  • dark matter


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